advantageously apply the great inductive methods of difference and residues. The lower animals possess certain faculties in common with man, but they are deficient in others, and hence by a diligent study of their actions we are enabled to distinguish how much of man's conduct is necessarily due to different faculties.

5. The science of Physiology is also a source of valuable information. The intimate nature of the relations between the mind and the organism, so strongly emphasized in the Aristotelian and Scholastic Philosophy which conceives the soul as the form of the body, receives more elucidation every day with the advance of biological science. In examining into the operations of sense, the development of imagination and memory, the formation of habits, and the transmission of hereditary tendencies, the advantage of a knowledge of the physical basis of these phenomena is obvious; but as all mental processes, even the most purely spiritual acts of intellect and volition, are probably accompanied or conditioned by cerebral changes, too much labour cannot be devoted to the study of the constitution, structure, and working of the organism. same time care must be taken to distinguish clearly between the two orders of facts. The mental state and its physiological accompaniment or condition are separated, as Professor Tyndall says, by an "impassable chasm." It is then not sufficient to explicitly admit once or twice, as most writers of the Sensist school do admit, that the neural and psychical events are divided by a difference which

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transcends all other differences, and then to forget, or lead the reader to forget, the vital character of this difference. The mental states must be treated and described throughout in such a way that no confusion between the two kinds of phenomena is caused to arise in the student's mind, and he must not be misled into supposing that a conscious process has been finally explained when its physical correlate has been indicated, or when the whole operation has been described in cloudy physiological language. It is, therefore, a grave violation of the most rudimentary maxims of philosophical procedure, and an unpardonable abuse of nomenclature, in a work of professedly scientific character, to call the neural concomitant the physical "side" or "aspect" of a sensation, and to speak of "waves of emotion" or the "glandular nature of the affections."

6. Hand in hand with Physiology goes Pathology, the complementary science of organic disease; and the opportunities presented in the investigations connected with this branch of knowledge for the observation of mental activities in an isolated or abnormal condition will occasionally throw light on obscure questions. Somnambulism, illusions, hallucinations, and various forms of insanity exhibit particular mental functions under exceptional conditions, and not infrequently suggest or confirm explanations of special mental operations. Similarly, the study of those deprived of different senses

3 For some admirable remarks on the abuse of physiological terminology in describing mental states, cf. Dr. Martineau's Essays Philosophical and Theological, Vol. I. pp. 252-254.

may advance the scientific analysis of normal perception and the discovery of how much is due to the various faculties. But here again judgment is required, and we must be on our guard against assigning too much weight to irregular and exceptional cases. The emotional interest excited by abnormal occurrences may easily lead us to exaggerate their philosophical importance, and to forget that after all the proper subject-matter of our science is the mens sana in corpore sano. The reality of this danger becomes apparent when we find writers on Psychology founding their theories as to the nature of the soul, or of its cognitive operations, not on the observation of the activities of the normal healthy mind, but on dubious conjectures regarding some obscure ill-understood forms of mental aberration that appear perhaps once among a hundred thousand human beings.

We have here explicitly enumerated the various sources from which our science draws its materials, but, although it has only in recent times become customary thus to classify them in detail, they have been made use of by writers on the philosophy of the mind since the days of Plato and Aristotle. Some recent authors appear at times to believe that these methods of inductive inquiry are a result of modern discovery, and that surprising advances of an undefined character have been, or in the immediate future will be, effected by their means in our knowledge of the nature of the mind. A comparatively brief study, however, of Aristotle's great work on the soul, and of his supplementary treatises on special

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psychological questions, will show how fully he appreciated the value of these extended fields of information.*

The method pursued in Rational Psychology will be mainly deductive. From the truths established in the earlier part of our work as regards the life of the soul, we shall draw inferences as to its inner constitution; from the character of the activity we shall argue to the nature of the agent, from the degree of perfection in the effect we shall reason up to that of the cause.

The scope just assigned to Psychology is objected to by writers of widely different schools in this country, so it may be well to add a few supplementary remarks in defence of our position. Opponents we may divide into three classes. Some deny the possibility of a science either of Rational or Phenomenal Psychology. Others, admitting the existence of a genuine science of the phenomena of the mind, deny the possibility of any real knowledge regarding the nature or existence of the soul. Others, again, whilst allowing with this second class the value of Empirical Psychology, exclude from its treatment various questions, such as the freedom of the will, and the origin of intellectual ideas, on the ground that these are metaphysical or philosophical problems to be treated of elsewhere. As regards this last view, the divergence from us may be mainly one of method and classification. Provided these questions are satisfactorily discussed in some branch of Philosophy, it does not appear vital what department be selected. We may, however, point out that Psychology, the philosophy of the mind, seems to be under more distinct obligations to face these problems than any other science; and, in the second place,

M. St. Hilaire has shown clearly how accurate were the views of the founder of the Peripatetic school on the use of the inductive methods in Psychology. Cf. Psychologie d'Aristote, pp. lii-lxv.

as we have already stated, any attempt at adequate treatment of mental phenomena will inevitably involve some particular philosophical view as to the nature of our faculties.

The only sufficient answer to writers of the second class those who deny the possibility of a rational science of the soul-is to work out a systematized body of certain truths regarding its nature, and the relations subsisting between it and the body. This we will endeavour to accomplish in the Second Book of the present volume. That a work claiming to be a treatise on Psychology ought to make some such attempt seems so manifest that it is difficult to understand why the duty should be so uniformly ignored in English manuals. Locke's influence and the national distaste for metaphysical argument has had much to do with it, but probably the authority of the Scotch school has had still more. For it was to Reid and Stewart those most interested in a satisfactory exposition of the evidence bearing on the existence and character of the human soul naturally looked for a proper vindication of the subject. Unfortunately, idolatry of empirical fact and contempt for deductive reasoning reached a climax in the common-sense school. As a consequence, the worship of the Baconian method in its most exaggeratedly vicious form wrought that evil in the science of the mind which it would assuredly have effected, had it been as faithfully followed, in the study of external nature.5 Thus we find that whilst in Germany and other Continental countries mental philosophy was approached with a view to the solution of the most interesting and important problems that can occupy the human spirit, British psychologists have been seeking to convert their science into a mere natural history of psychical phenomena. Any attempt at a comprehensive treatment of our mental activities is

5 On the reaction against the pure Baconian doctrine of method in recent times, see Jevons' Principles of Science, Vol. II. c. xxiii. He remarks that its value may be estimated historically by the fact that it has not been followed by any of the great masters of science." (p. 134.)