UhliJh M^kft, '" '"'*^S^»See1 '^ «a«t>N-'>~!> QforttBll Ittioetaitg Slibratg Stiiaca, Htw l^otk • THE GIFT OF PRESrOENr WHITE MAINTAINED BY THE UNIVERSITY IN ACCORD- ANCE WITH THE PROVISIONS OF THE GIFT The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924012250274 SCIENCE AND THEOLOGY By the Same Author SCIENTIFIC METHOD ITS PHILOSOPHY AND ITS PRACTICE New Edition. Price los. 6d. net BLACKIE AND SON, LIMITED SCIENCE AND THEOLOGY Their Common Aims and Methods BY F. W. WESTAWAY BLACKIE AND SON LIMITED 50 OLD BAILEY LONDON GLASGOW AND BOMBAY 1920 Fa ^!:\%\Lo O, I wad like to ken — to the beggar-wife says I — The reason o' the cause an' the wherefore o' the why, Wi' mony anither riddle brings the tear into my e'e. — It's gey arC easy spierM , says the beggar-wife to me. — Stevenson. PREFACE One object of this book is to show on what evidence some of the great fundamental principles of science have been estab- lished, and to make clear that these principles are provisional only, since they are always liable to revision in the light of new knowledge. A second object is to present a picture of the structure and evolution of the universe as conceived in the light of the discoveries of the last forty or fifty years. But it is important to remember that the conception is only a conception. The difference between fact and hypothesis must be carefuUy discriminated. A third object is to show that modem science has become a great fundamental factor in human hfe and progress. Its continuous growth is a proof of its vitality, and its innumerable applications to our daily wants a proof of its ability. No reUgious system can possibly prevail if it cannot assimilate the great truths of science. The characteristic of the scientific mind is its determination to test every dogma, whatever the authority on which it reposes. A fourth object is to show that permanent and final truth, whether in science or in theology, is very rare and very hard to come by ; and that what we call truth is usually an affair of a greater or less degree of probability. The revelation of truth is conditioned by our ability to receive it. In this world it is always partial and incomplete. Reinterpretation of truths already established are therefore constantly necessary in the light of new knowledge. Most of the divisions amongst Christians may be traced to the fact that men have taken part of the truth as its whole sum and have ceased to look for further knowledge. The final object of the book is to appeal to each and every branch vi SCIENCE AND THEOLOGY of the Christian Church to abandon its claim to be the special favourites of heaven, and to abandon, too, all that this imphes ; for instance, ecclesiastical exclusiveness, exclusive validity of sacra- ments, dogmas, forms, and rubrics ; and to present a united front to the common enemy. It is of little avail for the student to seek a philosophic basis for his theology before he has mastered the main principles of mathe- matics, of science, and of scientific method. If, for instance, he resorts to metaphysical arguments concerning the infinite before he has made himself acquainted with the nature of infinity in mathematics, he is violating the first principles of common sense. Training in scientific method has brought into being a thinking fraternity whose bond of loyalty is respect for the truth. Is it too much to hope that all students of theology will enrol themselves under the same banner ? The author is well aware of the incomplete treatment of several of the topics in the last chapter, and that the relations of certain vexed theological questions to the metaphysical and scientific principles discussed in the earher chapters are worthy of fuller discussion. Pressure of professional work compels him, however, to bring the book to a close, though he hopes to be able, later on, to expand the last chapter into a second volume, and to deal, in par- ticular, with the questions of (i) God and the problem of evU, (2) spirituaUsm and superstition, and (3) the permanent and the transient values of the Bible. So far as accuracy would allow, technical language has been avoided, and it is not assumed that the reader's knowledge of science and mathematics exceeds that of boys and girls of sixteen or seven- teen who are in attendance at a reasonably efficient school. A large number of authorities who are recognised as most eminent in their different departments of knowledge have been freely con- sulted. Those works to which reference has been chiefly made are named at the ends of the respective chapters. Special attention may be caUed to those marked with an asterisk. The non-scientific reader will find that the volumes belonging to the Home University PREFACE vii Library form a valuable sequel to several of the chapters ; the books are clearly expressed with a minimum of technical language, and include most of the latest researches and discoveries. (Note, in particular, those marked with two asterisks.) It is a pleasing duty to acknowledge the kindness of Professor D'Arcy Thompson and the Syndics of the Cambridge University Press for permission to make use of matter and diagrams from Growth and Form for the first section of Chapter X. ; of Professor A. Keith and Messrs. Williams & Norgate for permission to adapt, for the purpose of the diagram on p. 199, a genealogical tree from Ancient Types of Man ; of Professor T. C. Chamberhn and the University of Chicago Press for permission to quote from The Origin of the Earth for inclusion in sections six and seven of Chapter V. ; of the Open Court Publishing Company, Chicago, for permission to make use of certain passages, for inclusion in Chapter IV., from Mr. Bertrand Russell's Our Knowledge of the External World and Professor Schubert's Mathematical Essays. The author's greatest debt is to the late Lord Rayleigh, whose invaluable help was most ungrudgingly given for many years. F W W August, 1 91 9. Since the above was written, the claim has been made that Einstein's hypothesis of Relativity has been verified. But, more accurately, the results of the solar eclipse expedition have verified merely a particular consequence which Einstein said would logically follow from his hypothesis, namely, that light is refracted in a gravitational field. It certainly does not follow that the hypothesis as a whole is thus verified. True, the hypothesis seems to gather into its ambit more observed facts than the Newtonian hypothesis it supersedes, and, to that extent, probability is on its side. Further, the curvature of space, which the hypothesis demands, may also perhaps be conceded. But the hypothesis involves two consequences which at present seem impossible of accept- ance — the action of gravity across a void and the variability of time. A time which is not unique is contrary to the notion of the logical prin- ciple of non-contradiction, whereby a thing cannot both be and not be at the same time. (Compare Chapters III. and IV.) November, 1919. CONTENTS I. The Problems of Philosophy — §1- §•2. §3. §4. §5. §6. §7. §8. §9. §io. The Quarrels of Philosophers The Borderland between Philosophy and Science Psychology, Metaphysics, and Logic How the Mind acquires Knowledge The Categories. A priori Knowledge The Contrast of Subject and Object The different Schools of Philosophy Hypothetical and Natural Dualism (a) Substance . (b) Primary and Secondary Qualities Monism : its Logical Consequences (a) Idealism {b) Materialism Conclusion PAGE I 3 6 9 1 1 12 15 i6 i6 19 19 20 22 II. Opinion and Truth — § I. English and German Modes of Thought . § 2. In Opposition to Truth : Political Partisanship § 3. In Favour of Truth : Scientific Investigation § 4. Fact and Opinion § 5. Opinion and Conviction. Behef . § 6. Reason and Authority § 7. The Search for Truth 25 27 30 33 35 36 38 III. Matter — § I. The Conception of Great Numbers § 2. More about Hypotheses . § 3. The Kinetic Hypothesis of Gases . 43 44 48 SCIENCE AND THEOLOGY III. Matter icontd.) — § 4. Molecular and Atomic Hypotheses § 5. Molecular Dimensions § 6. The Periodic Law § 7. The Aether of Space § 8. Electric Hypothesis of Matter § 9. Radio-activity § 10. Transmutation § II. Laws of Conservation of Energy and Matter § 1 2. The Electrical Hypothesis difficult for a Layman to conceive § 1 3. Is the Hypothesis justified ? . . . . PAGE 50 51 53 54 58 63 64 67 69 70 IV. Infinity. Space and Time — § I. "Z^" . § 2. The Notion of Infinity .... § 3. Geodesic Lines. The Plane and Sphere compared § 4. " Points at Infinity " . § 5. Euclid's Parallel Postulate § 6. The Nature of Geometrical Axioms § 7. The Origin of Non-Euclidean Geometry . § 8. " Dimensions " . § 9. Flatland and Sphereland § 10. Measure of Curvature § II. Four-Dimensional Space § 1 2. The Obscurity of Riemann's Notion § 13. Can Riemann's Notion be put to a Practical Test ? § 14. The Properties of Space .... § 15. Time ...... § 16. Conclusion ..... 74 75 81 83 85 86 89 91 96 97 99 102 104 105 107 III V. The Genesis of the Earth — § I. The Evidence of the Spectroscope § 2. The Visible Universe § 3. The Nebular Hypothesis . § 4. The Nebular Hypothesis untenable § 5. The Meteoritic Hypothesis also untenable § 6. Professor Chamberlin's Sun-bolt Hypothesis § 7. The Hypothesis developed § 8. The Earth's Infancy 113 121 126 127 130 132 133 137 CONTENTS XI V. The Genesis of the Earth {contd.) — § g. The Final Shaping of the Earth — (i.) The Forces concerned (ii.) How the Forces acted § I o. The Dawn of Geological Time § II. The Origin of the Universe VI. The Evolution of Animal Species — § 1. The Hypothesis of Organic Evolution § 2. The Classification of Animals — (a) Homology and Analogy {b) Principles of Grouping in Classification (c) Species . First Test — Degree of Resemblance (d) Species : Second Test — Hybridisation (e) The Origin of Species — (a) Not due to a Creative Act (;S) Species arose by Natural Selection § 3. Cells and Cell-Division .... § 4. Geological Considerations — (a) The Geological Age of the Earth {b) Fossilised Animal Ancestry § 5. Variation and Heredity — {a) The Kinds of Variation {b) The Causes of Variation § 6. Natural Selection : The Survival of the Fittest § 7. Confirmatory Evidence — {a) Embryological Analogy (J)) Vestigial Structures g 8. Evolution in Retrogression PAGE 140 146 152 '53 156 158 159 159 161 166 167 170 174 177 181 182 183 VII. The Evolution and Antiquity of Man — § I . The Emergence of Man from Pliocene Times . . 185 §2. Early Rationality . . . . .188 § 3. The Successive Advances during the Pleistocene and Recent Periods . . . . . .189 §4. Palaeolithic Man. ..... 192 § 5. Palaeolithic and Neolithic Civilisations . . .194 §6. Early Types of Man . . . . -195 § 7. The Evolution Hypothesis is unproven . . . 200 xn SCIENCE AND THEOLOCxY CHAP. VIII. Life and Consciousness — § I . The Structure of Molecules. Valency § 2. Molecular " Compounds " or " Aggregates " § 3. The Simpler Organic Compounds. Carbohydrates and Fats ...... § 4. More Complex Organic Compounds. Proteins § 5. Still more Complex Organic Compounds. Colloids § 6. The Living Cell ..... § 7- The Origin of Life .... § 8. The Living Organism: Materialistic and Vitalistic Hypothesis not acceptable § 9. The Hylozoistic View of Mind and Matter § 10. Mind, Consciousness, Personality §11. Life as a Category .... 203 206 207 209 210 212 214 218 222 226 228 IX. Instinct and Intuition — § I. Animal and Human Instinct . . 232 § 2. Inconceivability . . . . .237 §3. Necessary Truth . . . . 240 § 4. Innate Ideas . . . 244 § 5. Perception and Intuition . . .247 § 6. Intuitive Knowledge ..... 249 § 7. The Intuitions of Great Minds . . . .251 § 8. Are the known Senses the only Gateways of Knowledge ? . 253 X. Probability — § I. Fundamental Differences of Opinion — (a) The Limitations of Magnitude in the Organic World (6) Analogous Forms in the Inorganic and Organic World (c) Mathematical Relations in Organic Forms (d) The Forces within the Living Cell . (e) The Survival of Human Personality . § 2. Mathematical Probability § 3. Fundamental Quantitative Notions § 4. Inevitable Uncertainty in the Theory § 5. Non-Calculable Probability § 6. Intuitive Probability in the Solution of Every-day Problems 25s 258 259 263 265 268 269 271 273 276 CONTENTS xiu CHAP. XI. Causation — § I. Causation in Dynamic and in Static Systems § 2. Cause and Effect. Reason, Result, Conditions § 3. The Mark of Causation . § 4. Plurality of Causes § 5. Regression of Causes § 6. The Law of Universal Causation § 7. The Uniformity of Nature § 8. The Metaphysical Problem PAGE 281 283 285 286 288 289 290 XII. Theology and Religion — § I. Knowledge and Faith § 2. Inspiration § 3. The Application of Criticism to the Bible . § 4. Does God exist ? § 5. The Nature and Attributes of God § 6. The Metaphysicians' " Absolute " § 7. The Creeds § 8. Miracles § 9. The Virgin Birth and the Incarnation § 10. The Resurrection § ri. Heresy and Intolerance . § 12. Immortality .... § 13. Religious Individuahsm versus Ecclesiasticism § 14. Conclusion .... 294 296 298 303 307 310 313 316 317 328 331 333 340 343 The things which are seen are temporal, but the things which are not seen are eternal. St. Paul. When they who condescend to tutor us Do prompt to deck false systems in Truth's garb, And tangle and entwine mankind with error, And give them darkness for a dower, and falsehood For a possession, Then one may feel resentment like a flame. Browning. Sanabimur, si modo separemur a coetu : nunc uero stat contra rationem, defensor mali sui, populus. Itaque id euenit, quod in comitiis, in quibus eos factos praetores iidem qui fecere mirantur, quum se mobilis fauor circumegit. Eadem probamus, eadem reprehendimus : hie exitus est omnis iudicii, in quo secundum plures datur. Quum de beata uita agitur, non est quod mihi illud discessionum more respondeas : ' Haec pars maior esse uidetur.' Ideo enim peior est. Non tam bene cum humanis rebus agitur, ut meliora pluribus placeant : argumentum pessimi turba est. Seneca. SCIENCE AND THEOLOGY CHAPTER I THE PROBLEMS OF PHILOSOPHY i I. The Quarrels of Philosophers It has been said that most philosophic systems are so many spectres — so many enchanted corpses which the first exorcism of the sceptic reduces to their natural nothingness ; that the mutual polemic of these systems is like the warfare of shadows : as the heroes of Valhalla they hew each other to pieces, only in a twinkling to be reunited and again to amuse themselves in other bloodless and indecisive contests. Why are there such fundamental differences of opinion amongst philosophers ? Why does the philosopher of one school refuse to admit that the philosopher of another school possesses any philo- sophical knowledge on the subjects that he treats ? Which is right, Monist or Dualist, Materialist or Idealist, Empiricist or Rationahst ? 2. The Borderland between Philosophy and Science It is a perfectly natural thing for the uninstructed plain man to place implicit rehance on the evidence of his senses. He sees the sun in its daily journey from east to west across the sky, and, Uke the ancient astronomers, he makes the assumption that the sun goes round the earth. To him the assumption involves no element of doubt ; to him it is not an hypothesis, it is a fact. When it is pointed out to him that the heliocentric h3^othesis provides a simpler explanation of the celestial motions and is more consistent with ascertained facts, he is puzzled, and his respect for authority may ' Parts of this Chapter appear in the Second Edition of the author's Scientific Method : its Philosophy and Practice. J (C982) I 2 2 SCIENCE AND THEOLOGY make him feel that his senses, at all events his sense of sight, may sometimes deceive him. If he becomes a student of science, he finds that many of his estabHshed notions are hopelessly wrong. In thinking about ordinary material things, for instance, he had always thought that they were coloured and resonant, quite independently of their relation to himself. The evidence of his senses he soon learns to accept with greater caution ; and he comes to understand that, so far as physics distinguishes reality and appearance, its criterion is not sense-perception alone, but consistency with an elaborate and complex system of more or less definitely established facts which embody the combined results of many perceptions and inferences. Science has continually to explain to uninstructed common sense that what reaUy happens is often something quite different from what appears to happen. The chemist performs a number of quantitative experiments, examines his results and detects amongst them certain common quantitative relations, sums up these constant relations as " generalisations," and so establishes the " laws " of constant, multiple, and reciprocal proportion, and the " law" of Gay-Lussac. These laws constitute important principles of chemistry and form the basis of the theory of the subject. Their justification is a great number of definitely established facts. They involve no assumption, no hypothesis, save that of the great induction of the Uniformity of Nature. But the chemist may now cast about for an " explanation " of these different laws. The atomic hypothesis covers and explains aU the facts of the first three, and Avogadro's hypothesis covers and explains all the facts of the law of Gay-Lussac. But these hypotheses are assumptions ; they are constructions of the chemist's mind ; they may or may not correspond to objective fact. In making these assumptions the chemist is tr5dng to get behind his observed facts, behind his phenomena, in order to discover the hidden secrets there. In doing this he is passing over the border-hne between the domain of science and the domain of philosophy. Such assumptions often prove to be wrong. Again and again in the history of science one hypothesis has been discarded in favour of another. But each hypothesis served at the time as an ex- planation to cover all the facts then known, and to link them up. Sometimes a new hypothesis has superseded an old one because the latter did not cover new facts and was therefore obviously wrong ; sometimes an old hypothesis has been discarded because seen to be held on insufficient grounds ; sometimes an old hypothesis has THE PROBLEMS OF PHILOSOPHY 3 been reduced to a simpler form : the mind always prefers a simple explanation to an elaborate one. Thus Copernicus showed that the Ptolemaic hypothesis was wrong ; Lavoisier, that phlogiston had no existence ; Darwin, that the fixity of organic species must be abandoned. Scientific knowledge has thus progressed not merely by the acquisition of new facts, but by correcting or discard- ing provisional hypotheses. Around and beneath the more settled portions of physical science, in the region where knowledge is growing in range and depth, there is constant conflict and controversy as to the truth of new conclusions, for the controversy centres round assumptions which are improved and often seem unprovable. Natural science, so recent a growth, is necessarily infected with error. It has been said that the truths of philosophy bear the samei relation to the highest truths of natural science as each of these j bears to the lower truths of natural science. But the term truth | is hard to define, and it would be safer to say that as each "widest generalisation of science embraces and consolidates the narrower ', generahsations of its own division, so the generalisations of philo- sophy embrace and consolidate the widest generalisations of science. It has, however, to be borne in mind that the main concern of science is with phenomena, for the investigations of science yield mainlyj phenomenal knowledge. Philosophy aims at a knowledge of the;i concealed reahties behind phenomena. There is, however, a great, deal of common ground between science and philosophy, and the purely speculative side of science properly belongs to philosophy. A philosopher unversed in science is Uke a man of science unversed in philosophy : neither can claim to be an authority in his own subject. Such philosophical points as are touched upon in this chapter are mainly logical, psychological, and metaphysical. With ethics and aesthetics the chapter has nothing to do. 3. Psychology, Metaphysics, and Logic Nominally, psychology differs from physical science only in the nature of its subject matter and not in its method of investigation. Regarded as an empirical study of the mind, it proceeds by methods of observation, experiment, and induction, analogous to those used in natural science. But the phenomena of the mind — thoughts, cognitions, judgments, beliefs, the facts with which psychology deals — are obtained by introspection, not, as in the case of the 4 SCIENCE AND THEOLOGY phenomena of natural science, through the senses. The difficulties of ascertaining the facts are therefore greater, and psychological interpretation is not always easily distinguished from metaphysical reflection. The psychologist cannot begin at birth to register the history of his mental operations ; he has to begin when a grown man, and the more cultivated his mind the farther away he is hkely to be from the primitive mental operations of his infancy. The system of knowledge which he attempts to formulate is thus of a highly problematical character, for about the beginnings of knowledge there can be no certainty. Text-books on psychology usually encroach on metaphysics. For instance, they sometimes attempt to investigate valid beliefs as conceived to exist for an ideal mind independent of the peculiarities of development of particular minds. There is, in fact, often such an admixture of metaphysical speculation with the empirical facts of psychology that the inteUigent reader is apt to attach a very sceptical value to the whole subject. Many of the ultimate problems of psychology are, however, necessarily metaphysical, and are never likely to be brought within the range of experimental investigation and solved by the methods of science. The newer experimental psychology is laboriously accumulating valuable facts, but many competent authorities are of opinion that it is attacking an un- solvable problem. At bottom, it is based upon the fundamental hypothesis that every phase of consciousness has its counterpart in nerve changes. That our conscious Ufe is inseparably associated with the changes that go on in the grey matter of the brain there is now hardly any room for doubt, but how the two are connected is unknown, and all explanations are conjectural. That our thoughts, cognitions, judgments, and behefs are nothing more than mere molecular changes in the grey matter of the brain is an hypothesis unsupported by any acceptable evidence. Unlike positive philosophy which contemplates the world as a whole from the point of view of natural science, and is satisfied with empirical evidence and with such inferences as can be drawn there- from, metaphysics aims at ascertaining facts concerning matter and mind and their relations beyond such knowledge as is based upon or is verifiable by particular empirical cognitions. The method of metaphysics is a distinctive dialectical method ; it begins by making a priori pronouncements, and by applying to these the rules of formal logic arrives at final conclusions which do not admit of any form of methodical proof, or any sort of appeal to experience. THE PROBLEMS OF PHILOSOPHY 5 Such conclusions, based as they are ultimately upon hypotheses which cannot be verified, are necessarily always uncertain. The traditional methods of metaphysics have come down to us from classical times. Great thinker as Plato was, he did not possess a very orderly mind, and although in his writings it is possible to discover nearly aU the principles of the methods which his more systematic pupil, Aristotle, afterwards formulated, the reader soon sees that Plato pinned his faith to a priori methods, had Httle sympathy with empirical methods, and was at heart a mystic. Aristotle's methods were different. All that was then known of natural science Aristotle mastered, and he was an original investigator as well. With him, observation and experiment occupied a foremost place. But the amount of indubitable positive knowledge then available was so little that he not only sometimes fell into grave errors but frequently feU back on a priori methods ; and although his flashes of intuition occasionally served him to good purpose, too often they lead to conclusions that do not harmonise with facts. The great weapon which Aristotle forged was formal logic, and for many centuries his followers showed a child-Uke faith in the omnipotence of reasoning according to the rules he laid down. In mediaeval times, especially, the most implicit trust was placed in Aristotehan logic, and a correct chain of deductive reason- ing from some original hypothesis dogmatically asserted was quite sufficient to stifle any doubts about strange conclusions ; and gradually the opinion became almost universal that the most important truths concerning reality could, by mere thinking, be established with a certainty that no subsequent observation and experiment could shake. And even to the present day there are philosophers who claim that a priori reasoning can reveal otherwise undiscovgrable secrets about the imiverse, and that therefore reality can be proved to be quite different from what by direct observation it appears to be. In the light of modem science, great numbers of old a priori errors have been refuted, and it is now natural to suspect a fallacy in any deduction of which the conclusion appears to contradict patent facts. The fallacy is not usually in the actual chain of reasoning : philosophers do not often make elementary blunders of that kind. It is traceable rather to an untenable original major premiss, adopted, perhaps, because of the royal confidence felt in some unexamined intuition, or because of some unsuspected pre- judice, poHtical, social, or theological. This major premiss, the original hs^iothesis adopted, may look plausible enough, but if the 6 SCIENCE AND THEOLOGY consequences logically traceable from it violate the first principles of common sense, the hypothesis must, without hesitation, be re- jected. A conclusion is by no means necessarily correct because the rules of formal logic have been exactly observed. The unacceptable conclusions of educated men are far more frequently traceable to false premisses than to false reasoning. The formal logic of tradition is merely a logic of consistency. As a well-known writer ^ on modern logic says, " the trivial nonsense embodied in this tradition is stiU set in examinations, and is defended as a propaedeutic, that is a training in those habits of solemn humbug which are so great a help in later life." Modem logic is something very different. Its chief business is to examine the validity of premisses, and it deserves the closest attention. In ancient philosophy the fimdamental contrast was between things as they appear and things as they are supposed to be in themselves ; between appearance and reahty. In modern philo- sophy the fundamental contrast is between mind and matter, between man who knows, and the things known to him. 4. How the Mind acquires Knowledge If we inquire into the origin of the stock of knowledge of which we are conscious, how it has been acquired, how it has been built up, and of what materials it is composed, we find it impossible to give entirely satisfactory answers, for we are forced to make assump- tions that admit of no ultimate verification. It is, however, easy to construct an hypothesis that wiU cover all the known facts, and of the different hjrpotheses in vogue it wiU sufiice to outline the details of one. We may assume that the mind is originally characterless like a sheet of white paper or an empty unfurnished room, or better stiU, perhaps, like a sheet of wax, for a sheet of wax may receive impres- sions and retain them. We may now imagine the mind to receive its first experience of external reality. For instance, let an electric torch be flashed across the field of vision. The mind experiences a sensation, namely, the sensation of a bright light. It is perfectly conceivable that a sentient being should have no sense but vision, and that he should have spent his existence in absolute darkness, with the exception of one soUtary flash of bright light. The whole content of his consciousness would then be Umited to this single sensation which his mind has received and registered. 1 Bertrand Russell. THE PROBLEMS OF PHILOSOPHY 7 Now an ordinary sentient being is endowed with other sense- organs besides that of vision, and from the first his mind is con- stantly experiencing, through the agency of these sense organs, sensations of smell, taste, hearing, sight, touch, and resistance (the muscular sense), in addition to sensations of pleasure and pain. All these sensations which the mind thus receives and registers form the raw materials of our stock of knowledge, and we cannot imagine our knowledge of external reality being derived from any other source. Every sensation impresses itself on the mind, and the mind is thereupon conscious of a vague organic feeling, a feeling that scarcely amounts to an awareness, certainly not the awareness of an object of any kind. Sensation is the most primitive form of mental product. But imiversal experience compels us to make a further assumption — that the mind, whatever the mind may be, is endowed with some kind of active power by means of which it can use the raw materials supplied to it in the form of sensations ; and this brings us to perception. Perception is the mental completion of a sensation. When the mind perceives, the vague feehng of awareness of the sensa- tion becomes focussed on some object and is localised in time and space. Perception therefore gives us knowledge of the thing pre- senting itself to the senses. Perception follows sensation and springs out of it. But in addition to localising external objects in time and space, the mind in the act of perception plays other important roles. • We imagined an electric torch to be flashed across the field of vision of a sentient being who had no other sense but that of sight, and who had hitherto spent his existence in darkness. The whole content of his mind is thus limited to the single sensation of a flash of bright light. Now suppose a second flash to follow the first. If there was no memory of the latter, the state of mind on the second occasion would simply be a repetition of that which occurred before. There would be merely another sensation. But suppose memory to exist, and that an idea of the first sensation is revived. Then there would arise in the mind of the sentient being two entirely new impressions, one the feehng of the succession of two sensations, the other the feehng of their similarity. Yet a third case is conceiv- able. Suppose the two flashes to occur together. Then a third feehng might arise, namely, the feehng of co-existence. These feehngs are fundamental and are not susceptible of further analysis. They are ultimate irresolvable facts of conscious experience. In order that they may be generated, the pre-existence of at least two 8 SCIENCE AND THEOLOGY sensations is required. Thus the materials furnished by the senses are taken up by the active mind, and their fundamental relations discovered. Unless the mind is assumed to be endowed with an active power, the discovery of these fundamental relations is inconceivable. Apparently, then, knowledge consists primarily of a series of perceptions, the materials for which are supplied, in the form of sensations, by the sense organs, and these materials are sorted out and rearranged by the active conscious mind. The mind has the power, however derived, of detecting co-existences, successions, and similarities amongst the materials supphed, and is thus able to synthesise knowledge. Complete knowledge consists of the per- ception of sensations and of the perception of the relations amongst these sensations. But it should be observed that most of om: sensations are not simple but complex. For instance, we pluck a rose and smell it, and we experience simultaneously at least three sensations, the visual sensation of colour, the tactual sensation of softness, and the sensation of smell. These complex sensations are blended and unified, and it is clear that the mind has the power to take this complex to pieces by analysis, and afterwards to rearrange it, with or without elements of other analyses, into new groups. We thus ascribe to the mind the powers of analysis and S5nithesis, though these are reducible to the more fundamental powers of perceiving co-existence, succession, and similaritj^. All explanations of the nature of perception are hypothetical, the relation of the perceived thing to the perceiving mind being exceedingly obscure. In the transmission of the message from the object to the percipient, some of the pathways are whoUy unknown ; for of the physiology of the brain and of nerve processes we know little, and of the relation between psychological and physiological processes we know nothing. It therefore follows that, since per- ception is the foundation on which the whole fabric of psychology is raised, and since the nature of perception is entirely hypothetical, psychology is less a body of positive knowledge than a body of hypotheses. We are able not only to acquire knowledge, but to retain it and to reproduce it when wanted. Sensations are more or less vivid and are perceived more or less clearly, but with the removal of the external object they tend to pass away though they leave images behind them, and these images, which we use in thinking and reasoning, we call ideas. The retentive power of the mind we call THE PROBLEMS OF PHILOSOPHY 9 memory. Further, we can not only recall knowledge out of conscious- ness, but we have the power of re-presenting it in consciousness. This re-presentative power is imagination. But these retentive and re-presentative powers are subsidiary ; the work they do is com- parable to that of labelling and docketing, sorting and re-sorting, in an office. It is subsidiary to the mind's main function of per- ceiving co-existence, succession, and similarity. This function of comparison impUes the power to divide and separate, conjoin and compose, analyse and sjmthesise. Judgment involves the dis- crimination and comparison of two or more terms or notions directly together ; reasoning the comparison of two terms or notions with each other through a third. Judgment and reasoning are thus both special forms of comparison, and are therefore directly de- veloped derivatives of the perceived fundamental relations afore- mentioned. So far we have made no assumption as to what the mind is, beyond suggesting what seems to be fundamentally necessary, namely, that it is an active something, capable of detecting relations amongst the materials supphed to it by the various sense-organs. If we assume that it can detect co-existence, succession, and simi- larity, and their opposites, in a word if it can compare things, everything else can be accounted for. As its knowledge grows, its powers grow. If, then, we need not assume that it was bom into the world, endowed with any other power than the one mentioned, what are the innate ideas about which philosophers hold such fimdamental differences of opinion ? 5. The Categories. A priori Knowledge In the perception of any of the relations of co-existence, succes- sion, and similarity, all involving as they do an act of comparison, the mind forms a primitive judgment. In the last resort a judgment invariably consists either in the discrimination of a difference or in the determination of an agreement between two or more things. Such fundamental and irreducible relations which the mind thus judges to hold universally among the particulars of experience are sometimes called categories. But while categories are grounded in experience and only formed on the contemplation of experience, they contain an inexperienced, inexphcable a priori element which we are driven by the necessity of thought to accept unquestioned. The mind contemplates experience and in it perceives the truth ; it does not create the truth. 10 SCIENCE AND THEOLOGY Different lists of categories have been drawn up by different philosophers, but any list can only be accepted provisionally. Every logical process necessarily originates in experience, and with fuller knowledge we may find it necessary to extend the hst of categories. For the present, the three, Co-existence, Succession, and Similarity, will sufficiently explain all the known facts of consciousness, and it is unnecessary to assume that the mind is endowed with any other original power than that of comparison in its different forms, or that it came into the world endowed with innate ideas of any kind. How the mind has acquired its power of perceiving the funda- mental relations amongst the facts of experience, and thus of pronouncing its primitive judgments, is unknown. The claim is sometimes made that the a priori element in these primitive judg- ments is the result of intuition, a subject to which we shall return in a later chapter. All other knowledge, save, perhaps, that of our own existence, is a posteriori knowledge, that is, empirical knowledge or knowledge derived from experience. A posteriori knowledge admits of verifica- tion and demonstration ; a priori knowledge does not. Some metaphysicians hold that, besides the categories, there are other a priori elements in our knowledge, that, for example, there is a personal God, or that the soul is immortal, or that every effect has a cause ; and on such assumptions they build up whole systems. But it is a cardinal rule of sound philosophy never to admit any facts a priori that admit of demonstration a posteriori ; and in accordance with this rule, as we shall see later, such metaphysical assumptions as those just referred to are neither justified nor necessary. Apart from the categories, in fact, none of our knowledge need be assumed to be innate. Consider, for example, how the mind probably establishes the maxim — Every effect has a cause. No universal or necessary truth can be established without a process of a posteriori induction. For all primitive judgments of the mind are individual. The mind observes a particular relation of succession, and pronounces the judgment that the first element in the succession is a " cause " of the second. The mind does not metaphysically announce that every effect 'must have a cause, but it declares that of this given effect there must have been a cause. Numberless similar individual judgments lead ultimately to the conclusion that every effect has a cause. The general maxim is obtained by a process of generalisation of the individual judgments. It is not, strictly, a generalisation THE PROBLEMS OF PHILOSOPHY ii of an outward experience, but of inward and immediate judgments of the mind, which carry in them the conviction of necessity ; and this necessity will therefore tend to attach itself to the general maxim. Even if the general maxim be regarded as a generalisation from outward experience, the mind obviously has to make a leap from that experience, necessarily limited, to the universality implied by the maxim. This leap may perhaps be justified by the stiU greater induction known as the Uniformity of Nature. Even so, the mind makes a leap beyond experience, and an a priori element is unavoidable. Thus absolute certainty can never be reached, only a very high degree of probability. To say, as some metaphysicians do, that the maxim, every effect has a cause, is entirely innate in the mind, that it is wholly a priori in its nature, and is whoUy independent of experience, is reminiscent of the scholasticism of a thousand years ago. 6. The Contrast of Subject and Object All consciousness must in the first instance present itself as a relation between the distinguishable parts of a duality, the person who is conscious and the thing he is conscious of. In order to be conscious at all, a person must be conscious of something. This contrast has been indicated, directly or indirectly, by various names : mind and matter ; person and thing ; subject and object ; self and not-self ; the ego and the non-ego. Mind, the ego, as knowing subject may therefore be at once connected and contrasted with its known objects. That an external material world exists in- dependently of our knowing it, and that its existence is not affected by our knowledge of it, is a belief that seems at once instinctive, inevitable, and necessary. Introspectively, at any moment, I am aware that I exist and continue to exist through changing states of consciousness. I know that I exist, but what I am, how my ego is constituted apart from my material organism, I do not know. I am not justified in assuming, from the evidence of introspection alone, that my ego is, for instance, a self-existent entity indestructible by the forces that ultimately destroy my material organism, or that my conscious- ness is to be attributed to anj^hing of the nature of a phantom-like double of the body. All that I can with certainty say is that when I concentrate my attention on the simplest act of perception, I have the irresistible conviction that I exist and that something else exists, and that I am conscious of both existences at the same moment. 12 SCIENCE AND THEOLOGY . We may therefore lay it down as a necessary conviction that consciousness gives us, as an ultimate fact, a knowledge of both the ego and the non-ego in relation to and in contrast with each other ; and it gives these elements in equal independence. In other words, mind and matter present themselves in absolute co-equality. This fact, however, is by no means universally accepted, and even when it is accepted it is accepted with such qualifications as it suits a particular philosopher to devise. In short, there are almost as many philosophic systems originating in this fact as it admits of various possible modifications. As might be expected, therefore, no consistently logical classification of the different schools of philosophy is possible. We may, however, give some indication of the broad distinctions amongst them. 7. The Different Schools of Philosophy The first distinction may be drawn between those who accept, whoUy and without reserve, the fundamental fact that mind and matter are separately clear and distinct to consciousness, and those who do not. Thus we have : A. Natural Dualists who regard mind and matter as real entities, distinct and separate from each other. B. Those who do not so accept the fact. Now it is undoubtedly true that the only positive knowledge we have of mind and matter is a knowledge of phenomena, and we may therefore suppose and consequently assert that all our knowledge of mind and matter is only a consciousness of various groups of mere appearances. But on the other hand, we might assert that the known phenomena of mind and matter must necessarily be referred to underl3dng substances or substrata of some kind, though actually unknown. Thus our class B may be subdivided into : I. Nihilists who deny that the testimony of consciousness can guarantee a substratum or substance underlying the phenomena of either the ego or the non-ego, and who assert that perceptions and ideas are the only reahties. II. Realists who affirm that the testimony of consciousness can guarantee the existence of a reahty, a substance or sub- stratum, underlying the phenomena of the ego and also of the non-ego. Realists are of many kinds, but they may be grouped into two main classes : I. Hypothetical Dualists who accept the testimony of conscious- THE PROBLEMS OF PHILOSOPHY 13 ness as to the ultimate duality of the ego and non-ego, but maintain that our consciousness gives us no direct knowledge of anything beyond phenomena ; that we therefore have no immediate know- ledge of the existence of matter or of mind, though we are compelled to assume the existence both of a substance or substratum in which the qualities of matter inhere, and also of an entity — mind, subject, or spirit — which perceives the facts of consciousness, though the nature both of the substance and of the perceiving entity is unknown. 2. MonisU who reject the testimony of consciousness as to the ultimate duality of the subject and object, the ego and the non-ego. Monists fall into two classes, according as they do or do not preserve the equilibrium of subject and object. (i.) Objective Idealists who hold the doctrine of Absolute Identity. They admit the testimony of consciousness as to the co-equality of mental and material phenomena, but not as to the antithesis of mind and matter as existent entities. They maintain that mind and matter are only phenomenal modifications of the same unknown absolute reality ; for since the impenetrabiUty of matter is intelligible only as a mode of resistance, the essence of matter must be some kind of power which it possesses in common with spirit. Matter and mind, or body and spirit, are therefore different aspects of a common substratum. (ii.) Those who deny the evidence of consciousness as to the co-equality of mental and material phenomena, and subordinate the one to the other entirely. Thus we have : {a) Idealists who maintain that the subject, the ego, was the original and is the only fundamental, and that the object, the non-ego, is evolved from it as its product. The funda- mental reality is psychical ; all matter is, at bottom, of the nature of thought. (6) Materialists who maintain that the object, the non-ego, was the original and is the only fundamental, and that the subject, the ego, is evolved from it as its product. There is nothing but matter. Mind, thought, consciousness are all by- products, epiphenomena, mere debris resulting from material processes. Life and consciousness cease absolutely with the disintegration of the matter with which they are associated. Thus both Idealists and Materiahsts beUeve in a reahty, but in a single reality. They are therefore at the same time Monists and Realists. It will be observed that all the different schools mentioned. 14 SCIENCE AND THEOLOGY Nihilists excepted, are Realists of some kind. The four main schools may be grouped in this way : 1. DuaKsts : (a) Natural Dualists (sometimes called simply ReaUsts). (b) Hypothetical Dualists (sometimes called Pheno- menalists). 2. Monists : (a) Idealists. (6) MateriaUsts. But the dividing hues are by no means so clear cut as this simple classification would seem to indicate. One school tends to shade off into another, and sometimes they are scarcely distinguishable. Indeed the terminology is most confusing, and is of very varying connotation. A few other terms require brief explanation. Sensationalism maintains that all our knowledge comes to us through the senses and refuses to admit that the mind is a co-con- tributor. Empiricism is sometimes confused with sensationaUsm, but empiricism admits that the mind must be something en- dowed with power to compare and contrast the data supplied by the senses, and thus to form judgments. All evidence derived from the senses is of particular truths. In every general truth there is an element of knowledge independent of such evidence, that is, independent of the data of the senses. Contrasted with sensational- ism is Rationalism, which asserts that the knowledge which comes to us through the senses is fallacious, for perception and experience can give us information concerning only particular instances, and can therefore never provide us with universal truths. The rationahst claims that reason is the sole source of real knowledge. Metaphysical rationalism must not be confused with theological rationalism, which is the doctrine that denies the existence of any supernatural revelation. But in both cases rationalism is an uncompromising assertion of the absolute rights of reason throughout the whole domain of thought. Both sensationaUsm and rationalism are dogmatic, as with both it is an article of faith that we have the power of acquiring complete knowledge, in the one case exclusively by perception, in the other exclusively by reason. In contrast with this dogmatism is Scepticism, which always doubts and sometimes denies the possibihty of our acquiring true knowledge at aU. Agnosticism asserts that our knowledge is limited to the pheno- mena of the external world and of the mind, and that we know THE PROBLEMS OF PHILOSOPHY 15 nothing of the ultimate reality which may lie behind phenomena. The agnostic disagrees both with the man who asserts and with the man who denies the existence of reaUty underlying phenomena, for neither can prove his case. The agnostic says that " he does not know " whether it exists or not. He wiU not agree even with the Hypothetical Dualist who assumes an unknowable. Agnosticism is negative. It differs from atheism, which positively denies the existence of a personal God, Agnosticism " does not know " whether there is a personal God or not. Positivism, like agnosticism, accepts all positive facts, but adopts a less negative attitude in all other ways. In its outlook it is some- what superciHous, stating that any man with a claim to intellectuality first discards his theology, then his metaphysics, and comes finally to rest in a contented acceptance of positive facts, though, curiously enough, one form of positivism fabricates a new kind of theology, or rather of religion, for itself. This " Religion of Humanity," which theoretically is admirable, is coldly received, mainly because of the grossly irregular life led by its founder. The less liberal t3rpe of theologian naturally dislikes not only atheism but also materialism, for a materialist is necessarily an atheist. And he has no great love for agnostics and positivists, or even for phenomenalists, and he invariably speaks of them in disparaging terms and of their materialistic tendencies. Towards Idealism he is much less hostile, though this attitude he finds it impossible to defend logically. 8. Hypothetical and Natural Dualism We have referred to the unknown real thing, the substratum or substance, which the Hypothetical Dualist assumes to underlie phenomena, the substance in which phenomena are supposed to " inhere." The term phenomenon is equivocal. In science it refers to the positive facts of perception, as distinguished from their causes. Scientific thought, in dealing with the concrete things of physical science, investigates their nature, their causes, and their effects, and so goes beyond mere sense-perception. It assumes the existence of atoms and of the aether, neither of which can be directly perceived at all. The atoms and the aether are inferred from a combination of observations and hypotheses. This inferential process is an imaginable one, for any conceptual region is necessarily conceived as though it might be perceived ; and by its means the atoms and the aether may be seen as if under an indefinitely powerful i6 SCIENCE AND THEOLOGY microscope. We can verify perceptually only up to a certain point ; the weakness of our senses leaves a great deal unperceived and imperceptible. This conceptual region would, if our inferences and hypotheses are correct, and if our senses were sufficiently keen, be perceptible. It has to be admitted, xmfortunately, that while the human understanding attempts to construct conceptual systems because it is not satisfied with the contents of sense-perception alone, it sometimes uses these conceptual systems of its own construction for the purpose of disparaging sense-perception as an illusion, although aware, of course, that it is from the data of perception that the suppositions of the conceptual system derive the whole of their vitality. Sometimes attempts are made to construct conceptual systems which are not clearly imaginable : that way lies inevitable danger. (a) Substance The Hypothetical Dualist's substratum is not phenomenal, for it cannot be made to appear to the senses. But although it is claimed to be more real than phenomenal, its existence is merely inferred. Since, however, the inference is not verifiable, we may deny its legitimacy, especially as the substratum cannot be made part of any conceptual system, for it is wholly unimaginable ; and this means denying the existence of the substratum, and therefore the existence of matter. Such a denial admits of no answer, though it certainly carries no conviction. It carries no conviction because we cannot bring ourselves to believe that the external world would cease to exist if our minds were annihilated. We feel bound to beheve in the existence of an external world which is quite independent of any percipient. " Substance," then, is the term given by the H5^othetical Duahst to that elusive yet necessary something, that obscure substratum, common to all material things, without being discover- able in any one of them, something which is never actually experi- enced, but something which is thought into things, nevertheless a real thing though a transcendent thing. It is some kind of undiscovered basic reahty, transcending all experience, and the aether of space may perhaps be regarded as the first stage of its phenomenahty. (b) Primary and Secondary Qualities All the " phenomena " of the external world known to us in sense experience are logically reducible to a comparatively small THE PROBLEMS OF PHILOSOPHY 17 number of common " attributes " or " qualities " which are (as the Hypothetical DuaUst claims) inherent in the assumed underlying " substance." These qualities are usually distinguished as primary and secondary. Primary qualities are those derived from our muscular sense of resistance; e.g., solidity, extension or size, and motion. They are those attributes of the external world that are regarded as independent of the observer. Secondary qualities are those derived from our other senses ; colour, sound, taste, smell, temperature, are examples. Science teaches us that the things of the external world have only the primary quaHties, and that these are among the causes of the secondary quahties, though the secondary also depend upon the existence of a sentient being. The primary qualities are permanent in time ; the same whether we are present or absent ; objective, and that about which there is no difference of opinion ; measurable in three dimensions of space, in duration of existence, and in energy. The secondary qualities are not permanent in time, do not exist in the absence of a sentient being, and are not satisfactorily measurable in any way except by referring their phenomena to primary standards. The secondary quahties have no independent existence in the external world : this is a scientifically established fact. If we think of the world or any part of it in the absence of aU sentient beings, we think of it as absolutely dark and absolutely sUent. The secondary quahties are really subjective reactions excited by the primary quaHties and objectified by association with them. The primary quahties are the most constant and unconditional in experience. Illusions are chiefly of seeing or hearing ; whereas to touch or grasp a thing usually produces conviction. Since it is in their primary qualities that things are most exactly measurable in dimensions, weight, and movement, it is natural that science should regard the primary queilities as pre-eminently real. But it must never be forgotten that the primary quahties are, as truly as the secondary, grounded in sensations and therefore liable to mis-interpretation. The nature of the H3^othetical DuaUst's " substance " is admittedly extraordinarily elusive : an imperceivable support of perceivable qualities necessarily seems to be something without assignable character, resembling nothing in experience and therefore explaining nothing. But if it exists at aU, there is one quahty we are bound to ascribe to it, and that is permanence in time, for this corresponds to the continuity of the experienced external world in the past and in the present. But, even so, permanence in time does not seem to help us to estabhsh any connection between other (0 982) ' 3 i8 SCIENCE AND THEOLOGY primary qualities and the assumed substance, and such terms as " underlie " and " inhere " are mere metaphors having no significant meaning. Still, the notion, though necessarily vague, of permanent transcendent substance, does give coherence and unity to the phenomena of the external world with which we are familiar. If we accept Hypothetical Duahsm, it is best to regard " sub- stance " as a category— as one of those unverifiable, unanalysable, fundamental, ultimate, concepts which the mind is driven by necessity to try to form. If we reject the category as illusory, the argument as to the possible coherence of phenomena seems to be reduced to nothing. If we accept it, that is, if we recognise substance as a category indicating the reaUty which is not immediately given to us in perception, yet felt to be necessary for the understanding of phenomena, and accept it either a 'priori or as the resiilt of reflection upon experience, the term seems to suggest something which is not very far removed from the ordinary matter of Natural Dualism after all. Yet the distinction may be usefully preserved. The distinction is just what is required to make the doctrine of transubstantiation intelligible, for a change in the substance of the sacramental elements, though unimaginable, is not inconceivable, all the qualities of the elements, primary and secondary, remaining imchanged. Ultim- ately, perhaps, physical science will solve the problem of matter and substance, and there can be Httle doubt that the primary qualities of matter — resistance, extension, weight, motion — ^will give us the key to the solution. The position of the Hypothetical Duahst as contrasted with that of the Natural Dualist ought now to be clear. Both are Reahsts, but in the case of the Hypothetical Dualist the real is only inferred ; to him, perceptions are perceptions of qualities only. In the case of the Natural Dualist, the real is apprehended immediately ; he takes the common-sense view ; he kicks against a stone and per- ceives it immediately and objectively — ^it is something soUd and extended before him, and it can be measured and weighed. That object he takes to be matter. Common sense revolts against regarding the object merely as an idea or as nothing beyond an integrated heap of sensations ; and the view of science is that of common sense. But the view is difficult to maintain in its entirety, for it is certain that om- positive knowledge, the knowledge that admits of no question, of external reality, is limited to our percep- tions of qualities. Whatever we know beyond these qualities is known by inference only, and such inferences seldom admit of complete verification. THE PROBLEMS OF PHILOSOPHY 19 9. Monism : Its Logical Consequences The greatest antithesis in present-day philosophy is that between the two monistic systems. Idealism and Materialism. Between these there is an unbridgeable chasm. A particular system is, however, sometimes prevented from falling into absolute Idealism or absolute Materialism, and is held in a kind of vacillating equili- brium, because in some of its opinions an idealistic tendency is counteracted by a materialistic tendency in others. It will be vmderstood that the term monism applies to any philosophic system which seeks to exhibit aU the complexities of existence, both material and mental, as modes of manifestation of one fimdamental reahty. Ideahsm assumes that aU fundamental reality is psychical, is, in fact, consciousness or mind. Materialism assumes that consciousness or mind is a mere by-product of the one fundamental reality, matter. Idealism reduces matter to mental elements. Materialism identifies thought or feeling with the nerve process which accompanies it. {a) Idealism We may consider Idealism first. Idealism maintains that whatever we know directly is reducible to ideas, and that ideas have an existence more real than the fleeting transient objects of sense ; and that the existence of matter is nothing but an illusion. But there are so many forms of Idealism, and its terms are used in so many senses, that it is difficult to come to close quarters with its fundamental assumptions. If " consciousness " be regarded as denoting the recognition by the mind of its own acts, and " mind " as that which thinks, wills, and feels, it may be said that consciousness is to the mind what extension is to the body. Though the analogy is imperfect it is suggestive, for both consciousness and extension are essential qualities ; we can neither conceive mind without consciousness, nor body without extension. But " mind " is sometimes spoken of as if it were precisely synon3anous with " spirit." Yet while mind, like spirit, is always regarded as an unknown conscious something, mind is never conceived as extended in space ; whereas spirit, though incorporeal, immaterial, and invisible, is usually conceived as so extended, to be invested in human form, and to be a personaUty somehow associated with the body ; it is always thought of as a substantial though immaterial entity which thinks, wills, and feels ; 20 SCIENCE AND THEOLOGY it is of necessity invisible if only because our hiiman sense of vision is limited to material things. But whereas a spirit is always con- ceived as an entity distinct from, though during Ufe closely associ- ated with, the body, the mind is seldom spoken of as if it were something that could exist independently of the body. The reader who takes up a book on IdeaHsm must assure himself of the precise meaning attached to these terms by the writer. If the writer describes mind and spirit as, for instance, " transcendent reahties of reflection," it may safely be assumed that he is trjdng to conceal, behind a rather pretentious definition, the fact that he despairs of finding a solution to the problem in hand. AU Idealists deny the existence of matter, though some of them say that all they really deny is the unknown substratum, " sub- stance." Some Idealists recognise the existence of spirit as an entity which thinks, wills, and feels. Others limit their recognition to the much vaguer thing, mind, still conceived, however, as an entity of some sort. Still others assert that, since all we positively know of mind are the facts of consciousness, we are not justified in assuming the existence of mind as any sort of separate entity ; and they maintain that the only real things in existence are mental facts, ideas.^ They make vague statements about a universal con- sciousness, all men's minds being alike in this respect, that each is a sort of temporarily separated portion of this universal consciousness. Now if we are sure of anything, it is that consciousness is personal and individual ; men's minds may in many respects be alike, but their differences are great and fundamental. A common conscious- ness is not only unimaginable, it is inconceivable. But more than this : Idealism altogether fails to explain the primary qualities of matter — extension, inertia, impenetrability. Despite his clever paradoxes, the Idealist cannot get rid of matter by dissolving it in mind. When material objects are in question, common sense refuses to admit that esse and percipi are identical. It is impossible to accept the ultimate logical conclusion of Idealism, that, with the expiring breath of the last sentient being, the whole universe dis- appears into nothingness. (6) Materialism To materiahsm, the only real world is the world of matter, the 1 A distinction may be drawn between two main forms of Idealism, the Platonic and the Berkeleyan, as they may be called. According to the first, the real consists of ideas, intelligible realities, eternal values, which are not dependent on mind for their being ; according to the second, all reality consists of minds and the contents of minds. THE PROBLEMS OF PHILOSOPHY 21 world of atoms with their primary qualities and motions. Life and consciousness are the products of matter and manifest themselves in complexities of atoms. From such complexities life is, in favour- able circumstances, spontaneously generated, and spontaneously generated Uving matter has, by blind chance, passed through the various stages of evolution until the human being reached his present state of development. The cause of the order of the world is not God but the evolution of matter. There is no God, no soul, no freedom, no immortaHty. AU psychical activity, all conscious- ness, is ultimately nothing more than a motion in and amongst the cells of the grey substance of the brain, possibly some form of wave- motion or of radiation set up by the movement. AU thoughts and feelings are not merely accompaniments but are identical with these nervous processes. The mind is nothing more than a function of the brain. All psychical facts are merely effects, though unexplained effects, of ceU movements in the brain. Thought bears much the same relation to the brain as bile does to the liver. The weakness of materialism lies not only in its vast assumptions, but in its failure to give any explanation of the ultimate origin of either matter or motion. It is impossible to beUeve that the thinking, feehng self, of which each one of us is conscious, is only an automaton; and even the materialist is forced to admit that we simply do not know whether there is any causal connection between the psychical facts and the physical changes which accompany them. Materialism fails to give any satisfactory explanation of the nature and origin of Mfe and consciousness. Common sense refuses to admit that consciousness is nothing but a movement of matter. The claims of materiahsm lead to far-reaching logical conse- quences. For the materiaUst asserts that all our vohtions are mere hnks in mechanical chains of bUnd causes and effects. ^ Now men act in consequence of motives, and their motives are thus the result of preceding facts, so that if we knew the antecedents of these facts and the laws that connect them, we could with infalUble certainty predict the consequences, immediate and remote. If Adam had been a super-mathematician, he might, automaton though he was — assuming that he was acquainted with all molar and molecular masses, their initial positions, direction of motions, velocities, and accelerations — ^have predicted the whole course of the world's history ; he might have written out a complete account, complete to the last detail, of the great European War; he might have predicted the date, place, and manner of death of the world's last mosquito ; nay, he might have foretold the very terms of the 22 SCIENCE AND THEOLOGY marriage-contract between the Tellurian Kaiser and the Martian Queen, to be sealed a couple of centuries hence. To the materialist, the human will counts for nothing and can effect nothing ; our every decision is the infalHble consequence of particular cerebral changes. The individual who, while balancing two courses, is tmder the impression that he is at Hberty to pursue either, is com- pletely under a delusion. The most calculating selfishness, the most heroic self-sacrifice, equally have been determined by chance aggrega- tions of molecules. Newton did not write the Principia, or Shake- speare, Hamlet ; they were not creative personalities ; they merely looked on while blind causes were at work, They were merely chance aggregations of molecules, constituting automata with fortuitously specially active cerebrations. So with all things that ever have been or ever will be produced. It is mere fancy, says the materialist, that we ever act from rational motives. No criminal is morally reprehensible ; he is simply morally irresponsible. How can a materialist give his support to any sort of penal code ? But to this question he can only logically answer that he, too, is irre- sponsible for his actions. 10. Conclusion It cannot be said that, although they are mutually destructive, either Idealism or Materialism is in itself a fundamentally illogical system. Each is logically worked out, but neither is acceptable because of the ultimate consequences traceable from its hjrpotheses ; in each case the consequences are such that common sense declines to accept them, and this really means a rejection of the h5rpotheses on which the systems are constructed. In fact, every system breaks down that refuses to accept the cardinal fact of the duahty of consciousness. Mind and matter are two entirely distinct things ■present to our consciousness ; they cannot be reduced the one to the other, in the first place because resistance is incompatible with the attributes of mind or spirit, and in the second because conscious- ness is inexpUcable by the qualities of matter. We may, if we like, recognise materialistic monism of body and an idealistic monism of spirit, combined in a unified dualism of substances, namely, the unified substances of body and spirit or matter and mind in the single personality of man. But the refusal to accept the great underlying fact of duahty of consciousness is an act of philosophic suicide. There is not a philosophic system but is open to attack, for every THE PROBLEMS OF PHILOSOPHY 23 system rests on hypotheses which, ultimately, are not verifiable. Dualism of both kinds is attacked, Natural Dualism because it takes too much for granted. Hypothetical Dualism because of the assimiption of unknown and apparently unknowable entities. Still, the ultimate consequences of Dualism are not so destructive as are the consequences of Monism. No philosophic system is closed and final. No philosophic system can give complete repose. Philosophic finality is stiU a philosophic dream. There are some philosophers who are less anxious to understand the world of science than to convict it of unreahty. They shrink from the laborious study of the detailed knowledge derived from the senses, and prefer to pin their faith on the wisdom, sudden and penetrating, which they believe will reach them by reflection and reasoning. In their more emotional moods a belief in the unreahty of the world of science arrives with irresistible force, and when this emotional intensity subsides they seek for logical reasons in support of that beUef . The attitude is altogether wrong. Like the man of science, the philosopher must lay aside his hopes and wishes when he studies his subject. There must be no shrinking from hard facts, no demand in advance that the world shall conform to preconceived desires. Knowledge of the universe is not hidden by a flimsy veil that can easily be torn aside ; it is very hard to come by. Common opinion prevails that metaphysical disquisition is idle, because the problems discussed are really never solved. It is quite true that philosophy has made greater claims and achieved fewer results than any other branch of learning. It has made many rash assertions and many rash denials. Yet some of the greatest thinkers since the age of ancient Greece have devoted their fives to philo- sophical problems, and no one would dream of calling them either shallow or insincere. That progress has been sfight is inevitable, for the great mass of philosophy is necessarily purely speculative. There is very Httle philosophical truth finally estabhshed, and additions can be made only at the cost of much labour, very slowly, and only then if the method of science is made the method of philo- sophy. Existing systems are often ingenious, even sublime, but they nearly always lay claim to finahty and completeness. And it is for this reason that many philosophers are stiU the playthings of the gods. 24 SCIENCE AND THEOLOGY PRINCIPAL BOOKS OF REFERENCE I. A. J. Balfour. Defence of Philosophic Doubt. 1. A. J. Balfour. ** Foundations of Belief. 3. T. Brown. Lectures on the Philosophy of the Human Mind. 4. Sir W. Hamilton. **Lectures on Metaphysics and Logic. (4 vols.) 5. G. W; Leibnitz. New Essays Concerning Human Understanding. (Trans, by A. G. Langley.) 6. G. H. Lewes. The Physical Basis of Mind. 7. J. M'CosH. *Examination of J. S. Mill's Philosophy. 8. J. S. Mill. *Examination of Sir W. Hamilton's Philosophy. 9. J. S. Mill. *Logic. (2 vols.) 10. K. Pearson. Grammar of Science. 11. H. Poincare. **Science and Hypothesis. (Trans, by " W. J. G.") 12. H. Poincar^. *Science and Method. (Trans, by F. Maitland.) 13. Carveth Read. **The Metaphysics of Nature. 14. F. C. S. Schiller. **Riddles of the Sphinx. 15. H. SiDGWiCK. *Philosophy : Its Scope and Relations. 16. H. Spencer. First Principles. 17. DuGALD Stewart. Philosophy of the Human Mind. 18. J. Ward. *Naturalism and Agnosticism. Useful Supplementary Volumes 19. J. B. Baillie. The Origin and Significance of Hegel's Logic. 20. A. Bain. The Senses and the Intellect. 21. W. B. Carpenter. Nature and Man. 22. T. H. Green. Philosophical Works. (2 vols.) 23. J. Grote. Exploratio Philosophica. (2 vols.) 24. I. Kant. Critique of Pure Reason. (Trans, by Max Miiller.) 25. I. Kant. Kritic of Judgment. (Trans, by J. H. Bernard.) 26. H. L. Mansel. Metaphysics. 27. H. L. Mansel. Philosophy of the Conditioned. 28. J. M'Cabe. Evolution of the Mind. 29. T. Reid. Active Powers of the Human Mind. 30. A. Riehl. Science and Metaphysics. 31. J. Veitch. Dualism and Monism. CHAPTER II OPINION AND TRUTH I. English and German Modes of Thought The contrast in the ideals of neighbouring nations is often remark- able, even when the nations belong to the same original stock. A particularly interesting example is afforded by Britain and Germany, between whom, during the great war, the contrast has been intensi- fied by a mutual severity of criticism. One well-known German recently wrote of us that we " preferred sport to labour, selfishness to sacrifice, and wire-pulling and patronage to efficiency ; that we despised knowledge, that we had no sense of organisation, and that we were shallow, conceited, and insincere." And the writer went on to try to prove that aU these and many other faults were traceable to the defects of our system of education. It is only natural that we should resent such criticism, but our sense of justice compels us to admit that not only is much of it justified but that there are certain phases of German education that command respect. German education has stimulated a thirst for knowledge ; it has made the nation alert to science ; it has made systematic co-operation a habit ; it has taught patriotic duty ; it has made the people industrious and thorough ; it has given them the strength of discipline ; and it has made profitable use of second-rate in- telligences. On the other hand, there can be no question that German education has deliberately been converted into a formidable engine for controlling conduct and swajdng purpose, for it tends to make the people think in herds ; thought is thus deflected from the piursuit of truth, and is converted into a kind of predominant instinct, and the workings of this instinct reason tends to become merely a means of justifying. Where a lie will serve their country better, Germans do not acknowledge any moral obligation to tell the truth 25 26 SCIENCE AND THEOLOGY to foreigners. They believe that they attain to righteousness and truth by surrendering their sense of both to their country, for to Germans it is Germany that makes truth true and righteousness righteous. In our natural dislike of the Germans we are often unjust to them. To single out the defects to which any t3rpe of mind is Uable, and offer that as the whole accoimt of it, is a misrepresentation that the strongest dislike cannot justify. It is sometimes said, for instance, that German scholarship is mere industry in acciunulation, accompanied by only a very small measure of fine perception. Both English and German t5rpes of mind have their special Hmita- tions and defects, more pronounced in the second- and third-rate men, and tending to disappear in the men who stand up above the common level. But the main reason why German scholarship should appear as the duU industry of mediocrities is a reason which does not reflect on Germany. Through the elaboration and organisation of its scientific work, a large number of mediocrities are always employing themselves in work in which they can be useful, in the industrious accumulation and digestion of masses of material — texts, historical facts, linguistic phenomena — and in the prosecution of systematised scientific research in hundreds of laboratories. The scholars of the first rank who make use of all this material and combine with it ability of a high order, originality, and imagination, are to some extent lost for foreign view among the crowd. In England, workers of the first rank stand out in much more individual prominence. Yet there is one fundamental difference between EngHsh and German scholars. Taught by Bacon, EngUsh scholars seem to have acquired an instinctive desire to accumulate aU possible facts before attempting to frame anything of the nature of a general law. But German thinkers tend to generalise before the accumulated facts afford the necessary justification. Their curious love of abstraction, and their desire to deduce a whole universe from a few general propositions, constantly lead to their illegitimate use of deductive reasoning ; they seem to be unsuspicious of the dangers of loosely established generahties. If we forget the leaders and consider merely the average men, there is probably Uttle to choose between the German and the Englishman. The former's subservience to his rulers leads to the acceptance of his rulers' opinions. The latter's faith in the party newspaper and the party politician leads equally to the acceptance of ready-made opinions. Neither the German nor the Englishman OPINION AND TRUTH 27 thinks for himself, the German because he is intellectually servile, the Englishman because he is inteUectuaUy lazy.^ It is characteristic of certaia nations, ourselves not excluded, that not only is the average man disincHned to think for himself, he is apt to make misstatements concerning the incidents of every- day Mfe. Passing feelings prompt stronger words than are justifiable, and the desire to interest hsteners leads to inaccuracy of statement, even to exaggeration. If there is exaggeration over triviahties, it is hardly likely that a more judicial tone wiU be adopted when the things discussed are momentous. It is not a question of intentional lying. Direct hes told to the world are as dust in the balance when weighed against the falsehoods of inaccuracy, and in this country the falsehoods of inaccuracy are in no smaU measure traceable to the political partisanship which is so characteristic of our national life. 2. In Opposition to Truth : Political Partisanship Party spirit affects for the worse even minds which are not commonplace. Each party has ends of its own, and is not always scrupulous in its method of attaining them. Each party claims to be able to set the world right, given only unlimited power. It would, of course, be untrue to say that any party is now corrupt, unless the term can be applied to the common practice of purchasing honours by making contributions to the party funds ; but each party does its best to draw to itself the allegiance properly belonging to the State. Each party passes hghtly over everything that would do the party harm, and dwells unduly on everything that increases its credit. Party men who are sincere and whose probity is beyond reproach may occasionally prove to be the most dangerous t3rpe of all, for they are apt to identify the cause of their party with the cause of righteousness. Votes^in Parliament are rarely affected by the arguments ad- vanced on one side or the other, for members are elected to give a general support to a particular party and to the policy with which that party is identified. The art of pohtical reasoning differs from the art of pure logic in this, that whereas the latter consists in drawing sound conclusions from premisses assumed to be true, the former consists for the most part in fitting plausible premisses ^ The embers of the great war are still glowing, and the author is therefore well aware that he may have appeared to be harsh and unjust in his judgment of a nation once great and no doubt to be great again. But the judgment is based upon facts well known for many years. 28 SCIENCE AND THEOLOGY to foregone conclusions. It is sometimes argued that in proportion as the process of forming opinions has been slow, circumspect, and deliberate, so should the process of changing them be equally slow, circumspect, and dehberate ; that we pay our opinions scant respect if we hold them at the mercy of the first clever advocate who assaUs them with arguments to which we cannot produce an answer on the spur of the moment. This is precisely the reason put forward by the party politician in excuse for the automatic registration of his vote. But he knows fuU well that he is not at Uberty to give expression to an opinion based upon the weighing of the evidence for and against a proposed measure : not that way lies his reward. A member of Parliament is elected by a majority, but a decision by a majority is, in general, opposed to the principle of judgment. Decision by a majority places aU members of the body on the same footing, and gives an equal value to the opinion of each. It makes no distinction between them as to competency, but allows equal weight to the votes of the persons most able, and of those least able, to form a correct judgment on the question to be decided. Attention is not paid to special fitness, only to numbers. An astute pohtician makes a careful study of the psychology of the crowd, for he well knows not only that the majority of the men who compose his local audiences are men with Uttle insight, with undeveloped inteUigence, with little knowledge, and with a narrow range of experience, but that a crowd as such is devoid of intellect and is possessed only of emotions. His stock of rhetorical devices enables him to make to the crowd a suggestion which they think is their own ; he thus anticipates the direction in which the crowd wiU move, and then loudly directs it to go that way. A crowd is a new entity differing in mind and will from the individuals who compose it. Its in- tellectual pitch is lowered, its emotional pitch raised. It takes on something of the character of a hypnotised subject. It tends to be irrational, lacking in self-control. At a pohtical meeting, and even in the House of Commons, it is interesting to watch how even highly intelligent men are carried away by the words of an orator — men who have every rhetorical device at their own finger-ends, and are fuUy aware of the artificiality of much of what the orator is sa3dng. Political prejudice is intensified by two special influences. The first of these is that of the newspaper press. The newspaper press of the last century was a great educational force. Day by day it exerted its power to influence its readers to better citizenship, and its enterprise was directed to the provision of authentic and accurate news. The newspaper press of the twentieth century is tending to OPINION AND TRUTH 29 substitute the business man for the man of letters. A certain number of present-day newspapers are seriously inaccurate in their state- ments of facts. There is competition amongst them not only for news but for news served up in an attractive form, and the desire to interest the reader is tending to become greater than the desire to inform him. Then, nearly every daily newspaper is a party newspaper. To ensure a large circulation it must provide its readers with what they want, and it must therefore make concessions to political prejudice, and sometimes even to uncultivated taste. It must push into prominence everything that is derogatory, and keep out of view ever5rthing that is favourable, to the character of the person whom it may suit the needs of the moment to belittle. The daily press is said to be independent, and that in a sense is true, but if it ceased to be partisan it would cease to be profitable. If all daily and weekly newspapers could be induced to confine themselves to facts and to state these facts accurately, the educational gain would be considerable, if only because people would then be under the necessity of forming opinions for themselves. Happily there is stni a section of the press worthy of the best British traditions. The Times, for instance, is rightly regarded as a great national asset. The second influence intensif5dng political prejudice is that of the legal profession. In his professional work every lawyer employs his energy, eloquence, subtlety, and knowledge " to make the worse appear the better reason." If he has a bad case, he sets himself to deceive the jury ; he uses every device known to rhetoric to appeal to the emotions and to obscure the facts ; he tries to injure the character of his opponents' witnesses. He is not paid to establish the truth but to win his case, and if he does this, few wiU think any the worse of him. In private life he may be the most moral, the most religious, of men. His professional work is supposed to meet a pubHc want, and in any case it forms an admirable training for the platform of party politics. Who then would deny him his reward, or begrudge the honours so liberally bestowed upon him ? Now the mere fact that he has acquired the art of making the worse appear the better reason makes him specially welcome to the ranks of a political party. Forensic advocacy in the law-courts does comparatively little harm, provided the judge is just and able, for insincerity is there recognised as a necessary part of the atmo- sphere. It is doubtful if any judge ever seriously listens to the concluding speeches of counsel for the defence and the prosecution, for his business is to get at the facts, not to listen to opinions which he knows to be partial. It is common knowledge that in a court of 30 SCIENCE AND THEOLOGY justice a lawyer is exempt from the ordinary rule that binds an honest man to use only arguments which he believes to be sound. But when the lawyer carries his professional methods into the pohtical arena, the unsuspicious pubUc are apt to accept his advocacy as that of a trustworthy person, whereas the advocacy is often fuU of subtleties of which the unsuspicious pubUc never dream. The advocacy is often insincere, purposely designed to intensify political prejudice, and sometimes deliberately dishonest. As it is too much to hope that a lawyer sh£iU be disquaUfied from holding political office, what can be done to get rid of the unfortunate influence he exerts in the pohtical world ? Probably nothing. The party system is the result of historical causes and social conditions, and developed in the same natural and largely accidental fashion as other elements in our working constitu- tion. It is so ingrained in EngHsh pohtical hfe that the evils are hardly Ukely to be uprooted, and as long as it remains it will certainly retain the props that give it greatest support. Still there is some reason to hope that a more judicial frame of mind on the part of an increasing proportion of the people wiU ultimately result from a more enhghtened education and from a more general training in scientific method. 3. In Favour of Truth : Scientific Investigation The student of scientific research must before aU things look upon himself as one who is summoned to serve on a jury. He has only to consider how far the statement of the case is complete and clearly set forth by the evidence. Then he draws his conclusion and gives his vote. And in acting thus, he remains equally at ease whether the majority agree with him or whether he finds himself in the minority. Scientific discovery almost always depends upon a man's looking at something in the dry light of the intellect, and isolating himself from previous thoughts both of himself and of others about it. In the higher sense of the word, discovery is the serious exercise and activity of an original feeling for truth ; the truth is sought, laboriously and silently, in the hope that it wiU suddenly flash out into fruitful knowledge. Many of the facts of science can be verified by repetition, and many of them measured quantitatively. Hence the investigator acquires a definiteness of grasp and a clearness of view of the rela- tions between cause and effect not otherwise attainable. By patient observation and experiment, by classification and inference, by OPINION AND TRUTH 31 framing and testing h5^otheses, by rejection of the inadequate, and by verification of the valid, the investigator establishes the generalisations of science. The great generaUsations of the in- organic world — the laws of the conservation of matter and of energy, the law of xmiversal gravitation, the laws of chemical combination — all these have resulted from the long-continued efforts of many minds. In the organic world there is more room for doubt. Such generalisations as the laws of heredity and evolution cannot, from the nature of the case, be estabhshed on a quantitative basis, but they are the result of equally zealous and careful research, and of their truth there is a greater or less degree of probabiUty. People unversed in science frequently impugn scientific method because of the hj^otheses to which science constantly resorts. But this is due to a misunderstanding of the nature of h5^otheses. An h37pothesis is devised to account for, to link together, and to explain, a group of objective facts. It is a mentally constructed and quite imaginary mechanism, and though a pictorial conception it is not in any way supposed to be necessarily representative of the actual machinery of nature. Whether, for instance, there are such things as atoms, and whether the atomic h5rpothesis is actujdly in accordance with nature, we do not know. We form an h3rpothesis in order to endeavour to deduce from it conclusions in accordance with facts, the supposition being made that if the conclusions to which the h3^othesis leads are verifiable, the h57pothesis is likely to be true. An hypothesis is only one conception among many possible alternatives, and must never be thought of as if it were a real fact. A scientific investigator hazards a number of hypotheses to explain a group of facts, and he tests them one by one to see which is nearest to the truth. For every hypothesis that proves acceptable, he may frame a score that may prove invaUd. An hypothesis is sometimes described as a guess. So at bottom it is ; but, after all, it is an intelligent guess and is the outcome of an inference from real data. It is wrong to call it idle speculation, though of course popular writers on scientific subjects are apt to indulge in speculations that are outside the scope of probabiHty. A layman necessarily faUs to appreciate a scientific hypothesis, for it is in the highest degree unlikely that he can understand the evidence that led up to it. If new facts are discovered that show an hjrpothesis to be invahd, a new hypothesis is devised to cover both the old facts and the new : this in itself is sufficient to show the provisional nature of an hypo- thesis. Of course an hypothesis may correspond to objective fact, and this may be ultimately proved. If, for instance, an optical 32 SCIENCE AND THEOLOGY instrument is ever constructed to render atoms visible to the eye, the atomic hypothesis will cease to be a mere supposition and become a fact. The great characteristic of scientific method is verification at every stage, the guaranteeing of each separate point, the culti- vated caution of proceeding to the unknown solely through the avenues of the known. Science demands that every hypothesis shall be treated as provisional until it has been confronted with fact, tested, and verified. The man of science always loves truth better than his system. He is ever ready to throw his system overboard, once new facts prove it to be wrong. He knows that without hypotheses he can achieve nothing, but he has the wisdom to reject all deductions from them unless such deductions are confirmed by experience. A credulous person is one who is uncritical in regard to beliefs, and shows an ignorant disregard of the nature of evidence. But in this world we have, for practical purposes, to beUeve or disbeUeve many things about which there is no certain proof. Life is too short to investigate everything for ourselves. But practical in- credulity is very different from the theoretical increduhty which governs the action of an unbeliever. A man who is theoretically incredulous, for instance, about ghosts, not only refuses to investigate them himself, but also denies that they are a proper subject for inquiry. Of course it is true that many hes have been told about ghosts, and that from time immemorial men have been predisposed to beUeve in them, and we are therefore naturally inclined to hold that all ghost stories are suspect. But this does not mean that science must not or cannot concern itself about ghosts, for the method of science is most valuable where the subject-matter makes it most difficult of adoption. Science refuses to accept fashionable assumptions, and it always suspects just those dogmas that are repeated most often and with the greatest confidence. Thus, when disbelief in ghosts became an article of faith, then was the time for science to concern itself about them, for it scented danger in the orthodoxy of disbelief. Its business is to be sceptical about denial as much as about assertion, and, being sceptical, it knows when scepticism has stiffened into incredulity. For instance, the h3^othesis has been advanced that ghosts are aetheric memories. The hypothesis has been derived from analogy. We know that sensations are constantly impressing themselves on the mind. The impressions vary greatly in strength ; some may possibly be transient and some obliterated ; others are certainly permanent. Some return often, some seldom. Now it may be OPINION AND TRUTH 33 conceded that everything that happens makes an impression on the surrounding matter and on the aether, though such impressions are often imperceptible to the senses. Such impressions certainly vary greatly in strength. We do not know enough about the properties of matter to understand what the ultimate nature of the process may be, but it is quite legitimate and in keeping with the modem trend of physical science to suppose that a phenomenon originally perceptible to the senses may impress itself on the aether, continue to exist aetheriaUy, though now imperceptible, and become again perceptible under favourable conditions. Such an hypothesis would account for most of the authenticated cases of visible ghosts, and of audible but invisible ghosts ; also for the fact that the visible ghosts are always seen wearing the clothes they wore in life. If such an hypothesis is put forward — and it certainly seems to cover the facts — it is the business of science dispassionately to examine it : it has no interest in the result one way or the other. If sufficient evidence is forthcoming to justify the hypothesis, science accepts it ; if not, science rejects it. Science has but one aim, and that is to discover the truth. 4. Fact and Opinion When a witness reports that he saw an object of a certain shape or size, or at a certain distance, he describes something more than a mere sensation, and his statement implies a judgment concerning the phenomenon. When, however, this judgment is of so simple a kind as to be wholly unconscious, and the interpretation of the appearance is a matter of general agreement, the perception may be considered to present us with a fact. Thus matters of fact are decided by an appeal to our own consciousness or perceptions, or to the testimony, direct or indirect, of the original and percipient witnesses. Doubts, indeed, frequently arise as to matters of fact in consequence of the diversity of the reports of original witnesses, or the suspiciousness of their testimony. The credibility of a witness to a fact depends on these conditions : that the fact fell within the range of his senses ; that he observed and attended to it ; that he possesses a fair amount of intelligence and a reasonably good memory ; and that he is a person of veracity even when his personal interests are concerned. Statements of fact rest entirely on the credit of known or assignable witnesses. With arguments it is different. These have a probative force quite independent of the person by whom they are propounded. The essential nature of opinion seems to be that it is a matter (C 982) 4 34 SCIENCE AND THEOLOGY about which doubt can reasonably exist, a matter concerning which two persons can, without absurdity, think differently. The exist- ence of an object before the eyes of two persons would not be a matter of opinion, nor would it be a matter of opinion that the sum of three and two is five. But when testimony is divided or uncertain, a supposed fact may become doubtful and therefore a matter of opinion. We are satisfied with the testimony that Caesar invaded Britain, and the invasion we regard as an indisputable fact. But we are not satisfied with the testimony as to the Noachian deluge which, though recorded as a fact, is obviously open to doubt, and is therefore a matter of opinion. The ultimate source of our belief or disbehef in matters of opinion is always a process of reasoning. Though it is scarcely possible to avoid forming a judgment, in some way or other, on almost everything which offers itself to the thoughts, yet many persons never exercise their judgment upon what comes before them in such a way as to determine whether it be conclusive and holds. The universal tendency of the human mind is to shrink from the trouble of thinking out any of its so- called opinions. People form the habit of letting things pass through their minds rather than of thinking about them. They become mentally indolent, too indolent to judge for themselves. Upon every conceivable subject they take their opinions ready- made. The memory thus becomes a store-house of unorganised facts and conventional ready-made opinions, and these eventually harden into irrational convictions. People are influenced in their opinion by the prevailing fashion. They fear singularity more than error ; they accept mmibers as the index of truth, and they follow the crowd. The disUke of labour, the fear of unpopularity, the danger even of setting up individual opinions against established convictions, contribute to strengthen this inclination. People take their opinions from their favourite newspaper, from the accepted beliefs of the society in which they move, or of the party or church to which they attach themselves, from tradition, from custom, from hereditary associa- tion, from social environment, from any source except that of careful independent thought. If they are asked why they believe a particular thing, they will say, I have it on good authority, or I read it in a book, or it is a matter of common knowledge, or every- body in the village beheves it, or I learned it at school. These replies mean that they have accepted information from others, without making any attempt to verify it, and without thinking OPINION AND TRUTH 35 the matter out for themselves. The causes of such behefs are thus obvious, though such causes are clearly not reasons. But the causes may become reasons if we are able to recognise that our teachers, our family, and our neighbours are competent and truthful persons, and possess adequate information. Reasons of this kind are probably the principal ground on which, in mature life, we accept the great mass of our scientific, historical, and other con- victions. I beHeve, for instance, that the diameter of the sun is about 850,000 miles for no other reason than that I beheve in the competence of the persons who have made the necessary observa- tions and calculations. In this case, the reason for my belief and the immediate cause of it are identical. The prevalence of an opinion is no proof of its soundness, for the opinion may have sprung from the most impure sources. Mere unauthenticated rumom:, or tradition, imperfect or unverified observation, hasty and illogical generalisation from a few facts, uncorrected by any analytical process, and even deliberate imposture, are often the originating causes of wide-spread opinions. Some- times these errors are deeply rooted in the popular conviction, and descend from generation to generation. Common superstitions and unscientifiic weather-lore are instances of this. Fallacies of all kinds are stiU accepted unquestioned, — for instance, that sugar is a bad thing for the teeth, and that the sun shining into a room tends to put the fire out. Even ministers of religion have been known to maintain that Adam and Eve were turned out of the Garden of Eden for eating of the forbidden fruit ; that this fruit consisted of an apple ; that the ark rested on Mount Ararat ; and that the crucifixion took place on Mount Calvary. Such statements point to an inexcusable neglect of careful reading. 5. Opinion and Conviction. Belief Men are apt to pride themselves that they are tolerant and respect the opinions of others, but their weakness is that they do not respect their own, because they come by them so easily. Opinions are quite different from convictions. A conviction is something that is acquired slowly, from knowledge and experience ; it is the reward that men get for intellectual honesty, and they are slow to get it because, when once it is theirs, they must act upon it or lose it. Often they are hardly conscious of its existence, or only discover it when there is need for action. No man fully realises what opinions he acts upon or what his actions mean, for opinions are less to be 36 SCIENCE AND THEOLOGY acted upon than to be talked about. The man who has clear and firm convictions is by them protected from the indiscriminate invasion of opinions, for he tests opinions by his convictions and, if they are contrary to his convictions, rejects them. Convictions have effect because they produce action. Convictions are active ; opinions are passive. The meaning of behef is less settled than that of knowledge, opinion, and conviction. It sometimes stands for the region of opinion, or the doctrine about which we are not quite confident, so that degrees of belief or of subjective assent are recognised. Belief admits of aU degrees of intensity, from the subjective feeling of " necessity," through degrees of probabihty, to doubt and sus- pension of judgment ; and again through degrees of improbability to disbeUef. Suspension of judgment implies that incompatible behefs are felt to be equally balanced in a mind susceptible to their influence at the same time. 6. Reason and Authority When a person forms an opinion without any appropriate process of reasoning and without compulsion or inducement of interest, but simply because some other persons whom he beMeves to be competent judges on the matter entertain that opinion, he is said to form his opinion on authority. If he is convinced by a legitimate process of reasoning from the evidence supporting the question, his opinion does not rest on authority. A large proportion of the general opinions of mankind are derived merely from authority, and are entertained without any distinct understanding of the evidence on which they rest, or the argumentative grounds by which they are supported. In order that a person may be recognised as a competent authority in matters of opinion, certain qualities are necessary. In the first place, he must have devoted much study and thought to the subject- matter. No person, however penetrating his intellect, can master any one of the more important branches of knowledge unless he devotes to it years of study and reflection. Four or five years' strenuous work at a university is usually a good beginning, but it would be absurd to call it more than a beginning. In the second place, the person's mental powers must not only be equal to the task of comprehending the subject but ought to be superior to the average. His mind ought to be more wide-ranging and far-seeing than that of ordinary people. He ought to be able to trace the OPINION AND TRUTH 37 remote consequences of a particular principle. In the third place, he must be exempt, as far as possible, from personal interest in the matter : honesty is indispensable. A man's judgment is often blinded by the ardour of contention, by the desire of gaining an argumentative victory over an antagonist, and by the dislike of a confession of error. The dislike of listening to unpalatable truths often induces a man to close his ears to evidence and arguments opposed to the views which he considers favourable to his own interest ; on the other hand, the desire to discover new arguments to support his views leads him to read the books and to frequent the company of only those persons whose opinions are in accord with his own interests. QuaHties which render a man a trustworthy authority in matters of opinion are much rarer than those which render a man a credible witness in matters of fact. Hence the honesty which induces a man to speak the truth is more common than that which induces him to form sound opinions. One clear indication of trustworthy authority is the agreement of competent judges. This is analogous to the agreement of credible witnesses. If ten credible witnesses agree, the value of their con- current testimony is more than ten times the value of the testimony of each. So with the joint probabiUty of the agreement of ten competent judges in a right opinion. Authority is both insidious and far-reaching in its action. It is contrasted with reason, and stands for that group of non-rational causes, educational, social, pohtical, and moral, which produces its results by psychic processes other than reasoning. At first sight, reason and authority seem to be opposed, but the one cannot be held to exclude the other. For a person who chooses his own guides chooses them by the light of his own reason ; he exercises a free choice and is therefore ultimately responsible. And it cannot always be assumed that an appropriate process of reasoning upon any subject is a better or wiser principle of judgment than a recourse to the authority of others. Where special attainments and experience are necessary for a safe decision, a man who prefers his own judgment to that of competent advisers certainly does not follow a wise course ; and when a man is necessarily ignorant of the grounds of decision, to decide for himself is an act of foUy. The theory commonly held is this. Everybody has the " right " to adopt any opinion he pleases. It is his " duty " before exercising this right, critically to sift the reasons by which such opinions may be supported, and so to adjust the degree of his convictions that they 38 SCIENCE AND THEOLOGY shall accurately correspond with the evidence adduced in their favour. Authority has therefore no place among the legitimate causes of belief. If it appears among them, it is as an intruder, to be jealously hunted down and mercilessly expelled. Reason and reason only can be safely permitted to mould the convictions of mankind. But the identification of reason with all that is good and authority with all that is bad, among the many causes of belief, is, as Mr. Balfour reminds us, a prevalent delusion. The tacit assiraiption so commonly made that reason means right reason is absurd. Reason can no more be made to mean right reason than authority can be made to mean legitimate authority. Authority moulds our ways of thought in spite of ourselves and usually unknown to our- selves. But when we reason we are the authors of the effect pro- duced ; we set the reasoning in motion and are responsible for all the consequences. If people disagree with us, we are apt to be so far uncharitable as to attribute their beliefs to causes which are not reasons. But only a very small number of the most important and fundamental beUefs are held by persons who could give reasons for them, and of this small number only an inconsiderable fraction are held in con- sequence of the reasons by which they are nominally supported. It is a noteworthy fact that beliefs which are really the offspring of authority, when challenged, invariably claim to trace their descent from reason. Needless to say, such an improvised pedigree is often purely imaginary. Even in those cases where we may most truly say that our beliefs are the rational product of strictly intellectual processes, we have in all probabiHty only to trace back the thread of our inferences to its beginnings, in order to perceive that it finally loses itself in some general principle which owes its origin to the influence of authority. 7. The Search for Truth The historian who sets out to record truth gives a faithful record of events, extenuates nothing, conceals nothing, and distorts nothing. He exercises the greatest care in selecting his materials, and abstains from inventing details to fill up gaps. Past ages can be recon- structed only after the most painstaking and minute research, and at the best history is a record honeycombed with false data which must for ever remeiin uncorrected. But few historians are free from prejudices of some kind, and their search for truth is not impartial. OPINION AND TRUTH 39 Very few ordinary people seem to search for truth. Some do not make the search because they are intellectually indolent ; some, because they have an exaggerated respect for authority and feel a deference to long-established custom ; some lack faith in their powers of forming an independent judgment ; some are tempera- mentally averse from remaining in any sort of doubt ; some seem to feel that truth is endangered if that side of it which they regard as particidarly theirs is submitted to scrutiny. Only the few resolve to be intellectually free. The consciousness of truth seems to involve both^ cognition and intuition. In the mind's attempt to discover truth, there are feelings of behef, hesitation, perplexity, and disbehef. Still the mind strives to know, and the success or failure is a knowing or not knowing. Truth, therefore, is essentially cognitive, and its primary tests are cognitive, namely, clearness and distinctness, and agreement with reality. But over and beyond that is the self-evidence of intuition. Necessary conviction never comes without definiteness of conception, rigour of verification, and the complete confidence of intuition. The essence of truth is the verifiable agreement of judgment with reality. Although one of the primary tests of truth is clearness and distinctness, it must not be assumed, as Descartes assumed, that clearness and distinctness are alone sufficient to estabUsh a judgment as necessarily true. The things which may be clear and distinct — definitions, generahsations, syllogisms, and the Hke — are usually things of otu own creation. But the great facts of the ruiiverse — hfe, the relation between mind and body, freedom, causation, infinity, God, and the rest — are never clear and never distinct. On the contrary, they are necessarily always obscure and always confused. If we imagine that we have formed clear and distinct ideas of them, we shall, on further examination, find that we are deceived, for our positive knowledge of them is nil. Unless verifica- tion of agreement with reahty is possible, complete confidence must not be placed in ideas to which we have contrived to give an appear- ance of clearness and distinctness, for such fabricated products of our own minds are ever Mkely to lead us astray. Suppose we wish to describe a tree which we can just discern at a distance through the fog. If we remain where we are, the descrip- tion is necessarily very imperfect and probably inaccurate. If the fog clears away and we draw nearer to the tree, we can make the description more complete and less inaccmate. If we walk round the tree and view it from many points, the description can be made 40 SCIENCE AND THEOLOGY still more clear, accurate, and complete. If we uproot the tree and cut it into sections, our knowledge of it increases further ; but however far we may carry our examination, we can never obtain complete knowledge of the tree. Our description, as far as it goes, may be clear, distinct, and adequate, and every stated fact we can verify. But the description cannot be complete, and oru idea of the tree, though true as far as it goes, does not contain the whole of the truth about the tree. As we obtain more facts, so additional truth to our idea of the tree becomes possible. But at every step our judgment is involved, and upon the truth or falsity of our judgment depends the truth or falsity of our knowledge. The popular notion is that a true idea must copy its reality. Certainly our ideas, especially of concrete things, are copies, more or less accurate, more or less complete. But absolutely faithful copies are never possible, inasmuch as the ideas are derived from the reports of the senses, in the imperfections of which they must share. Absolute truth is therefore never discoverable. We may, in fact, say that truth belongs less to ideas as such than to our judg- ment concerning their agreement or disagreement. The excellence of an idea Ues in its being clear, distinct, and adequate ; the truth of our judgment concerning it depends upon its agreement with reality. Fundamentally, truth is the relation between an idea and reality. Our idea of the Copemican system of astronomy is clear and distinct and apparently adequate, but to people who lived in pre- Copernican times, so was the Ptolemaic system. Yet the relation between the idea and reality in the latter case is now demonstrably false ; and who can say but that new evidence may some day be brought forward imperiously demanding the supersession of the Copemican hypothesis ? Modern hypotheses concerning the constitution of matter seems to be clear, distinct, and adequate, but no competent person would be rash enough to say that the truth-relation between idea and object has been finally established. It is improbable that our ideas of electrons, of atoms, and of the aether are faithful copies of reality. Sometimes possible alternative hypotheses are put forward and are equally consistent with aU the truths we know, and then for subjective reasons we choose between them. It would be poor scientific taste and bad economy to choose the more comphcated of two equally well-evidenced conceptions, and the choice of the less comphcated gives us the maximum satisfaction. Truths gradually emerge from facts and become new facts, in their turn to produce new truths, and so on indefinitely. OPINION AND TRUTH 41 But the truths to which thought attains are always finite ; indeed, perception of truth is the recognition of the finite amid all the chaos of apparent infinity : it is the hearing of music where before there was only a conflict of discords, the result of cognition and intuition working upon an almost limitless number of combinations of sound. When we hear it we feel sure that the choice is not arbitrary ; it seems to us discovery rather than invention ; and so it is with all the truths which the mind of man estabHshes. The absolutely true, that is what no further experience wiU ever modify, is that ideal vanishing point towards which we imagine that all our temporary truths wiU some day converge. Since all knowledge is relative, all truth is relative. Absolute truth is as far distant as perfect wisdom. We have to five to-day by what truth we can get to-day and be ready to-morrow to call it falsehood. Much of what appeared to our ancestors to be absolutely true we now know to be only relatively true, and therefore at least in some measure to be false. As our limits of experience are extended, we detect errors in supposed truths and catch ghmpses of higher truths, and the ghmpses serve to inspire us with the hope that continued search will meet with great reward. Any great generalisation newly established is not the ultimate fact of an old series ; it is the first fact of a new. Every general law is only a particular fact of some more general law presently to reveal itself. There is no enclosing wall. No truth is so sublime but it may be trivial to-morrow in the light of new thought. It is well for our peace of mind that a great thinker is so seldom let loose in the world, for existing truths are all at the mercy of a new general- isation. The world owes far more to those who tear up our conven- tions than to those who calmly accept them. But conventional society is an affair of elegance in trifles ; it has neither ideas nor aims except to increase its comfort ; it hates those who attempt to disturb its serenity by delving for the truth. Complete repose is ours if we care to clothe ourselves in the dogmatism of the first creed that comes along. But if we make that choice we close the door to truth. Repose and truth cannot both be ours. To engage in an unremitting search, and thus to keep ourselves for ever unanchored and afloat, compel us to submit to the inconvenience of discomfort and suspense ; but, after all, the inconvenience is worth while, for the unremitting search may unexpectedly enable us to open the doors of truth we never dreamed of. The wise man knows that in his search for truth he can never 42 SCIENCE AND THEOLOGY meet with complete success. If any one is so vain as to persuade himself that he has attained it, he is self-deceived. Claiming to know all things, he is convicted of not knowing himself. Scrupu- lously honest he may be, but he possesses a modicum of wrong- headedness which induces him to refuse to accept the view that truth is necessarily impregnated with error ; to him truth is a perfectly pure and crystal-clear abstraction. What does it matter if we do not enjoy the full confidence of those who foohshly believe that they have already attained complete knowledge of the great mysteries of the Universe ? Better that than forfeit our intellectual honesty. It is often necessary to accept apparently irreconcilable proposi- tions, and to recognise that in our present state of knowledge it is impossible to correlate them with each other, or make them fit in with anything like a symmetrical system of thought, though each claims a place in the fuU circle of truth. The hypothesis of the sovereignty of a Supreme Intelhgence, for example, is difficult to correlate with the hypothesis of man's free-will, yet because we find it difficult to bring the two hypotheses together in a logical sjmthesis, that in itself is no justification for denying the one or the other. We must ever beware of the intellectual atmosphere of past ages when there was no recognition of dominant natural law. Plato and Aristotle were intellectual giants, and took all knowledge for their province ; but their ignorance was necessarily profound. In our search for truth it is of httle avail to go to them for help, though as guides to wisdom they are still supreme. PRINCIPAL BOOKS OF REFERENCE 1. A. J. Balfour. **Foundations of Belief. 2. A. J. Balfour. **Theism and Humanism. 3. H. WiLDON Carr. **The Problem of Truth. 4. R. W. Emerson. Essays. 5. W. James. *The Meaning of Truth. 6. G. C. Lewis. *The Influence of Authority in Matters of Opinion. 7. A. SiDGWiCK. Fallacies. 8. A. SiDGWiCK. The Applications of Logic. 9. S. P; Thompson. *The Quest for Truth. CHAPTER III MATTER I. The Conception of Great Numbers Before proceeding with the main subject-matter of this chapter it is necessary for the non-mathematical reader to get some idea of the significance of large numbers. A million is a thousand times a thousand, i.e., looo x looo or (lo xio xio) x{io xio xio). This may be conveniently written 10* X 10* or 10*- A billion is a million of milHons, i.e., lo* x lo® or lo^^- A trillion is a million of billions, i.e., lo^^ x lo® or lo^*. A quadrillion' is a million of trilUons, i.e., lo^^ xio* or lo^*. And so on. A quadrilUon is a number so vast as to be almost beyond compre- hension. It is a biUion of biUions, and even a single biUion is very much larger than is usually recognised. We give some illustrations. On a very bright starry night, the total number of stars visible to the naked eye is about 3000. This number, if counted at the rate of five per second — very rapid counting, of course — would be counted in ten minutes. At the same rate it would take about fifty-five hours to count a million. The number of letters in the Bible is rather over 3 J millions ; it would therefore take a Uttle more than a week to count them, counting five per second and keeping on day and night. A bniion is a million of millions, and at the same rate of counting would take 7000 years to count. Hence, if an ancient Babylonian had commenced, say, in the year 5000 B.C. to count a billion, and had counted at the rate of five per second, keeping on day and night to the present time, he would not yet have finished his task. And yet this is only a billion. To coimt a trillion (10^^), would take a milhon times as long ; to count a quadrilhon (lo^*), a billion times as long, i.e., seven thousand billion years. 43 44 SCIENCE AND THEOLOGY The area of England and Wales is 58,000 (or 5-8 x 10*) square miles, i.e., 2-3 x 10^* square inches. Now consider some fairly fine sand, viz., of such a degree of fineness that there are 41 grains to the inch. This would give 1681 to the square inch, or about 70,000 to the cubic inch. If the whole surface of England and Wales were covered with this sand to the depth of a foot, the total number of grains of sand would be about 2 x 10^°, i.e., 200 trillions, and this is the approximate number of molecules estimated to be contained in a single cubic centimetre of gas at normal temperature and pressure. The area of the whole water surface of the globe is about 150,000,000 square miles, and the average depth of the oceans is about 12,000 feet. The number of cubic feet of water in aU the oceans is thus 5 x 10^^ cubic feet, and the number of drops ^ of water in aU the oceans about 2-4 x 10^^, i.e., about twenty-four quadrilHons, and this is approximately the estimated number of molecules in the amoimt of water contained in an ordinary wine bottle. The number of molecules in a single drop of water is about 1-7 X 10^^, i.e., about 1700 trilUons. To coimt this number at the rate of five per second would take nearly twelve billions of years. If we imagine a sohd sphere the size of our globe uniformly covered with water to the depth of about 7 J inches, the 'volume of water would contain approximately 17 x lo^i drops, and each drop would contain 17 x 10^^ molecules. 2. More about Hypotheses A hundred years ago, John Dalton, during his researches on the chemical composition of various substances, analysed two gases, olefiant gas and marsh gas, both of which consist of carbon and hydrogen, and obtained the following results : Olefiant gas, 857 per cent of carbon and 14-3 per cent of hydrogen. Marsh gas, 75 per cent of carbon and 25 per cent of hydrogen. 1 The word " drop " applied to liquids is rather indefinite, but the medical man sometimes uses it instead of the technical term " minim " ; 480 such drops make a fluid ounce. A gallon of water contains approximately 277 cubic inches, and a. cubic inch of water contains approximately 277 drops. A cubic inch contains between 15 and 16 cubic centimetres, and a cubic centimetre contains 18 drops. An ordinary port or sherry glass contains 3 fluid ounces, or 80 cubic centimetres, or 1440 drops. Drops of water of the size 18 to a cubic centimetre may be discharged from a vertically held pipette with a nozzle 3 millimetres in diameter, at a drop rate of one per second, the temperature being 20° C. A variation in any one of these factors will lead to a variation in the size of the drops. MATTER 45 On comparing these numbers he found that the ratio of carbon to hydrogen in olefiant gas is 6 : i, whereas in marsh gas it is 6 : 2. The mass of hydrogen combined with a given mass of carbon is therefore exactly twice as great in the one case as in the other. Further researches followed, and in all the compounds examined analogous regularities were discovered. The uniformity led Dalton to generalise his results and so to formulate the empirical law of multiple proportions. He now cast about for an explanation of the composition of matter, an explanation which would entail the formulated law as a mere consequence. He felt convinced that he could not account for the facts unless he assumed that the structure of matter was discontinuous, and he therefore made the assumption that all elements consist of minute indivisible particles termed atoms (the idea of molecules came later) having a definite weight ; that the atoms of each elementary substance are alike among themselves and are different from the atoms of every other element ; that the atoms of a chemical compound are not alike among themselves but are composed of the different elements by the interaction of which they are produced. This is the famous atomic hypothesis. If the truth of the hypothesis be. granted, the laws of chemical combination may be deduced directly, and are made intelligible. There is therefore a presumption in favour of its truth. Moreover, the possibility of its truth has been strengthened by a vast number of confirmatory experiments. It is, however, important to note that the hypothesis is nothing more than a mentally constructed and quite imaginary mechanism accounting for the facts. We must be imder no illusion that our pictorial conception is representative of the actual machinery of nature. All we know is that chemical reactions take place as if the hypothesis were true. The function of an hypothesis is of such fundamental importance that the reader's further attention must be drawn to it. Physical science seeks to explain natural phenomena by means of the minimum number of the simplest and most probable fundamental assumptions it is possible to conceive. An explanation is a descrip- tion in greater detail, giving a feeling of greater satisfaction. But sometimes we get this satisfaction by an explanation which is not a description of additional facts but of some hypothetical inner mechanism. In science there is no such thing as a final explanation. We may discover reasons that wiU give us temporary satisfaction, but we can never get back to ultimate causes. 46 SCIENCE AND THEOLOGY In physical science the term generalisation is often used to denote the process of passing from a Hmited number of facts to a multitude of unexamined cases which we believe to be subject to those in- variable conditions that determine the common nature of the phenomena. Such a generahsation is often known as a law or a " law of nature." Laws of nature may be looked upon as the generahsed results of experience conveniently stated in a form suitable for future reference. Such a generalisation is at first usually more or less empirical, and it necessarily has a hypothetical basis, for it can never be altogether free from conjecture. At bottom a generalisation is an h5^othesis. When we proceed to imagine an explanation, an important part of the h5^othesis which we then formulate consists in developing some kind of mechanical model whereby we may visualise the un- known processes involved in the experimental facts and mathe- matical laws. But the chance of hitting upon objective reahty by such guess-work is obviously remote, and we must never forget that our hypothesis is nothing more than a mentally constructed mechanism. Hypotheses do not always perform quite the same function, and distinctions are sometimes drawn between descriptive hypotheses, hjrpotheses of law, and hypotheses of cause ; but they all have the same fundamental common factor, that is, we assume the existence of some sort of secret inner organisation of real things and processes. Conjecture enters largely into the everyday work of men of science, who are thus constantly constructing working hypotheses which, it is confidently felt, will be verifiable by experiment. For instance, when it was discovered that Glauber's salt gave a definite pressure of water vapour, the supposition was made that other hydrates would do the same, and experiment showed that the supposition was correct. The hypothesis was thus replaced by absolute fact. Such working hypotheses are subjected to verifica- tion as quickly as possible, and if verifiable they become truths of great fertUity. But hypotheses like the atomic hypothesis and the aether hypothesis perform a different function from the everyday working hypotheses of science. Their entire verification is improbable. Their main function is to play the part of an imaginary mechanism welding the facts together and provisionally accounting for their known inter-relations. If after formulation they cover new facts they are strengthened ; if they clash with new facts they are either revised or abandoned altogether. MATTER 47 Thus the existence of a class of fictitious phenomena which cannot be perceived by the senses is assumed by science ; properties are assigned to them, similar to those known to be true of a class of real phenomena which can be perceived by the senses ; and the nature of the phenomena thus conjectured may be modified at any time in order that new facts may be brought within the hypothesis. Certain important hypotheses, for instance that of the wave theory of Ught and the atomic hypothesis, have proved eminently useful, since they have reduced very complex relations to a few simple laws. Further, the main hypotheses of physics tend to a imiiication in which the axioms of mechanics are the first principles. Yet hypo- theses must be employed with caution and judgment, for their too free use leads to confusion with objective fact. Metaphysical hypotheses are, from their very nature, necessarily unverifiable, and since some of the best-known hypotheses of physical science are really metaphysical, the danger of their constant use is an inevitable tendency to give an objective reaUty to things which in the beginning we knew to exist only in our own minds. The specific claims of science are seriously weakened if the limits of possible knowledge are not recognised, and if facts and speculation are not clearly distinguished. The term theory should not be used for hypothesis. More properly it refers to an aggregate of conceptions, wholly or partially verified generalisations, and laws, which constitute the abstract statements of some branch of science. Thus we talk of the theory of chemistry. In science it is sometimes said that many quantities are assigned on " theoretical grounds " which cannot be verified. For instance, it is stated that 600,000,000,000,000 Ught undulations strike the retina of the eye in one second. Clearly this number could not be verified by direct counting. Is, then, the statement a fact or an hypothesis ? It is neither. It is an inference which follows, quite logically, from the two premisses : (i) the length of light undulations and (2) the velocity of hght ; and its vaUdity depends upon the vahdity of these premisses. Now, of the two premisses, the second is definitely known as a fact, but the first — the wave-length of Ught — is involved in inferences from a particular hypothesis as to the nature of Ught. Evidently an inference from an hypothesis faUs short of objective fact, and a sUght presumption in favour of its corresponding with reaUty is aU that we can give it. The study of chemical changes from a quantitative standpoint has led to four great generalisations from the results of actual 48 SCIENCE AND THEOLOGY experiments. Three of these — the laws of constant proportion, of multiple proportions, and of reciprocal proportions, respectively — refer to quantitative relations as respects weight ; the fourth — Gay-Lussac's law — expresses quantitative relations with regard to volume, and relates to matter in the gaseous state only. When these laws were first formulated they were based on the results of comparatively few experiments, and they were largely of the nature of unverified hypotheses, but they have since been confirmed by an overwhelmingly large number of additional experiments performed by chemists all over the world. It is true that, ultimately, they all rest upon an hypothesis that has never been completely verified, but that hypothesis, the far-reaching induction commonly known as the Uniformity of Nature, is co-extensive with all human ex- perience, and the hypothetical element underl5dng the four great laws is thus reduced to the vanishing point. The laws therefore rest firmly on the basis of experiment, have really passed beyond the stage of hypothesis, and are true statements concerning objective facts. It is for this reason that the wise teacher of chemistry provides his pupils with a sufficient number of experimental facts, and sees that they clearly apprehend the four great generahsations based upon those facts, before he introduces any serious considera- tions of a theoretical nature. But he then feels the need of a more comprehensive explanation, and the necessary introduction of the atomic h5^othesis at once adds to the difficulty and danger of his work, for his bed-rock facts now begin to take a subordinate place. 3. The Kinetic Hypothesis of Gases Matter exists in three states, gaseous, liquid, and solid. The nature of gases and liquids is understood, but relatively little is known about the conditions that determine a soUd. It is the nature of a gas to " fill " completely any closed vessel that may contain it ; it never settles ; and, if given an opportunity, it fills uniformly any other available space, larger or smaller, offered to it. It matters not whether the space is a vacuum or is already occupied by another gas. Each gas by diffusion seems to fill the whole space uniformly as though the other was not present. A given quantity of gas will expand without assignable limit, and it is therefore impossible to imagine it as a homogeneous substance absolutely filling the space in which it exists. We cannot imagine that the same amount of substance absolutely fills, at different times, volumes different from each other. The difficulty at once disappears if we make the MATTER 49 assumption that the gas consists of a number of discrete particles which can be pressed nearer together or allowed to move further apart. In fact, we seem to have no alternative but to form this h5rpothesis as soon as we discover that a gas does not settle, is compressible, and is diffusible ; and all observed experimental facts are completely satisfied if we further assume that at ordinary temperatmres and pressures the particles are at great average distances apart, and that they are in perpetual motion and have perfect elasticity. To these discrete particles the name " molecules " has been given. Further, since every gas is found by experiment to be homo- geneous throughout any space that may contain it, we infer that all the molecules of the same gas are alike ; that since a constant relation, that of inverse variation, is found between pressure and volume, we infer that the pressure is produced by the impacts of the molecules and is proportional to the degree in which they are crowded together ; that since a constant relation is found between volume (or pressure) and temperature, we infer that an increase in temperature increases the velocity and therefore the kinetic energy of the molecules ; and, finally, that since the volumes of different gases that combine are either equal or stand to one another in the ratio of small whole numbers, we infer that chemical union consists in the combination of different kinds of molecules of which there are, at the same temperature and pressure, equal numbers in equal volumes of different gases. AU these inferences are fuUy justified, though, of course, they depend upon the first assumption that a gas reaUy does consist of discrete particles which are called molecules. The reader should dwell upon the results of the different experiments and on the inferences drawn therefrom. It should be quite clear, for example, that the phenomena of diffusion seem to point con- clusively to the fact that gases (and Uquids) must consist of particles in motion relatively to each other, capable of penetrating the inter- spaces between the similar particles of contiguous bodies. Given sufficient time, diffusion may go on even between solids, as has been shown when gold and lead are placed in intimate contact with each other. It was at one time thought that the particles of a gas repelled one another, but in reality they tend to move together ; and when the temperature is lowered so much that, owing to the reduction of the kinetic energy of the molecules, this tendency can produce its effect, the gas condenses to a liquid. But the essential difference between the gaseous and liquid states is confined to the surface of the