In spite of all that has been done in the way of applying scientific principles to religious ideas, there is much that yet remains to be accomplished. Generally speaking science has only dealt with the subject of religion in its more normal and more regularised forms. The last half-century has produced many elaborate and fruitful studies of the origin of religious ideas, while comparative mythology has shown a close and suggestive relationship between creeds and symbols that were once believed to have nothing in common. But beyond these fields of research there is at least one other that has hitherto been denied the attention it richly deserves. When the anthropologist has described those conditions of primitive culture amid which he believes religious ideas took their origin, and the comparative mythologist has shown us the similarities and inter-relations of widely separated creeds, religious beliefs have yet to submit to the test of a scientific psychology, the function of which is to determine how far the same principles apply to all phases of mental life whether religious or non-religious. Moreover, in addition to the normal psychical life of man, there is that vast borderland in which the normal merges into the abnormal, and the healthy state into a pathologic one. That there is a physiology of religion is now generally admitted; but that there is also a pathology of religion is not so generally recognised. The present work seeks to emphasise this last aspect. It does not claim to be more than an outline of the subject—a sketch map of a territory that others may fill in more completely.

From another point of view the following pages may be regarded as an attempt more completely to apply scientific principles to religious beliefs. And it would be idle to hope that such an attempt could be made without incurring much hostile criticism. In connection with most other subjects the help of science is welcomed; in connection with religion science is still regarded as more or less of an intruder, profaning a sacred subject with vulgar tests and impertinent enquiries. This must almost inevitably follow when one has to face the opposition of thousands of men who have been trained to regard themselves as the authorised exponents of all that pertains to religion, but whose training fails to supply them with a genuine scientific equipment. It should, however, be clear that an attitude of hostility to science, veiled or open, cannot be maintained. Mere authority has fallen on evil days, and in all directions is being freely challenged. There is increasing dislike to systems of thought that shrink from examination, and to conclusions that cannot withstand the most rigorous investigation. And if science really has anything of value to say on this question it cannot be held to silence for ever. Sooner or later the need for its assistance will be felt, and the self-elected authority of an order must give way. It is, moreover, impossible for science with its claim, sometimes avowed, but always implied, to cover the whole of life, to forego so large a territory as that of religion. For there can be no reasonable question that religion has played, and still plays a large part in the life of the race. Whatever be the nature of religion, science is bound either to deal with it or confess its main task to be hopeless.

Whether or not it is possible to apply known scientific principles to the whole of religion will be a matter of opinion; but the attempt is at least worth making. So much that appeared to be beyond the reach of science has been ultimately brought within its ken, so many things that seemed to stand in a class by themselves have been finally brought under some more comprehensive generalisation, and so become part of the 'cosmic machine,' that one is impelled to believe that given time and industry the same will result here. And it should never be forgotten that one aspect of scientific progress has been the taking over of large tracts of territory that religion once regarded as peculiarly its own; and just as psychology and pathology were found to hold the key to an understanding of such a phenomenon as witchcraft, so we may yet realise that a true explanation of religious phenomena is to be found, not in some supernatural world, but in the workings of natural forces imperfectly understood.

The defences set up by theologians against the scientific advance may be summarised under two heads. It is claimed that the 'facts' of the religious life belong to a world of inner experience, to a state of spiritual development which brings the subject into touch with a super-sensuous world not open to the normal human being, and with which science, as ordinarily understood, is incompetent to deal. In essence this is a very old position, and contains the kernel of 'mysticism' in all ages, from the savage state onward. This position involves a very obvious begging of the question at issue. It assumes that all attempts to correlate religious phenomena with phenomena in general have failed, and that all future attempts are similarly doomed to failure. Of course nothing of the kind has been shown. On the contrary, the aim of the present work is to show that no dividing line can be drawn between those states of mind that have been and are classed as religious, and those that are admittedly non-religious. For various reasons I have dealt almost entirely with those conditions that are admittedly pathological, but I believe it would be possible to prove the same of all normal frames of mind and emotional states. Any human quality may be enlisted in the service of religion, but there are none that are specifically religious. It is a pure assumption that the religious visionary possesses qualities that are either absent or rudimentary in other persons. Human faculty is everywhere identical although the form in which it is expressed differs according to education, the presence of certain dominating ideas, and the general influence of one's environment. To admit the claim of the mystic is to surrender all hope of a scientific co-ordination of life. It is quite fatal to the scientific ideal and involves the re-introduction into nature of a dualism the removal of which has been one of the most marked advantages of scientific thinking.

Moreover, whatever views we may hold as to the ultimate nature of 'mind' the dependence of all frames of mind upon the brain and nervous system is now generally accepted. We may hold various theories as to the nature of mind, we may, with the late William James, treat the brain as merely a 'transmissive' organ, but even on that assumption—on behalf of which not a shred of positive evidence has been offered—the frames of mind expressed are determined by the nervous mechanism, and thus the laws of mental phenomena become ultimately the laws of the operation of the nervous system. The 'facts' of the religious life thus become part of the facts of psychology as a whole. Its 'laws' will form part of psychological laws as a whole, and religious experiences must be handed over for examination and classification to the psychologist who in turn relies for help and understanding on various associated branches of science.

Closely allied to the claim of the 'mystic' that his experiences bring him into touch with a world of super-sensuous reality, is the attempt to prove that science is incapable of dealing with anything but "in the first place, the endless ascertainment of facts and the physical conditions under which they occur, and in the second place to the criticism of error." Well, no one denies that it is part of the work of science to ascertain facts, or even that its work consists in ascertaining facts and framing 'laws' that will explain them. But why are we to limit science to physical facts only? All facts are not physical. If I have a head-ache, the unpleasant feeling is a fact. If I feel hot or cold, angry or pleased, think one thing ugly or another beautiful, my feelings are as much 'facts' as anything else that exists. Nay, if I fancy I see a ghost, or a vision, these also are 'facts' so far as my mental state at the time is concerned. So also are my beliefs about all manner of things, and often the most important facts with which I am connected. Facts may be objective or subjective. They may exist in relation to all minds normally constituted, or they may exist in relation to my own mind only; or, yet again, they may exist only in relation to certain states of mind, but they do not, nevertheless, cease to be facts.

Now the business of science is to collect facts—all facts—classify them, and frame generalisations that will explain their groupings and modes of operation. It talks of the facts of the physical world, the facts of the biological world, the facts of the psychological world, and so forth. This last group comprises all sorts of feelings and ideas, beliefs and experiences. Some of these facts it calls false, others it calls true—that is, they are true when they hold good of all men and women normally constituted, they are not true when they hold good of isolated individuals only, and can be seen to be the product of misinterpreted experience, or arise from a derangement—permanent or temporary—of the nervous system. But true or false they remain facts of the mental life. They must be collected, grouped, and explained exactly as other facts are collected, grouped, and explained. They fall within the scope of science, to be dealt with by scientific methods.

There is really no escape from the position that so far as religious 'facts' are parts of mental life, religion becomes logically a department of psychology. The substantial identity of all mental facts is quite unaffected by their being directed to this or that special object. As mental facts they are part of the material that it is the work of science to reduce to order. And as mental facts religious phenomena are seen to follow the same 'laws' that govern mental phenomena in general. It is perfectly true that we cannot test and measure the material of psychology with the same definiteness and accuracy that the chemist applies to the subject-matter of his department; but that may be due to want of knowledge, or to the extreme complexity and variability of the matter with which we are dealing. And if it were true that the same tests could not be applied in psychology that are applied elsewhere, this would be no cause for scientific despair. It would only mean that fresh tests would have to be devised for a new group of facts, as every other science has already, as a matter of fact, created its own special standard of value.

The second of the two lines of defence consists in the bold assertion that the religious interpretation of subjective phenomena is itself in the nature of a true scientific induction. The methods of science are not repudiated, but welcomed. But it is argued that the non-religious explanation of religious phenomena breaks down hopelessly, while the religious explanation fully covers and explains the facts. If this were true, nothing more remains to be said, and we must accept this dualistic scheme, however repugnant it may be to orthodox scientific ideas. But is it true? Is it a fact that the non-religious explanation breaks down so completely? Hitherto the course of events has been in the contrary direction. It is the religious explanation that has, over and over again, been shown to be unreliable, the non-religious explanation that has been finally established. Insanity and epilepsy, once universally ascribed to a supernatural order of being, have been reduced to the level of nervous disorders. All the phenomena of 'possession' are still with us, it is only our understanding of them that has altered. And before it is admitted that the phenomena described as religious can never be affiliated to the phenomena described as non-religious, it must be shown—beyond all possibility of doubt—that their explanation in terms of known forces is impossible. As I have said in the body of this work, the question at issue is essentially one of interpretation. The 'facts' of the religious life are admitted. Science no more questions the reality of the visions of the medieval mystic than it questions the visions of the non-mystic admittedly suffering from neural derangement. The crucial question is whether we have any good reason for separating the two, and while we dismiss the one as hallucination accept the other as introducing us to another order of being? I do not think there is the slightest ground for any such differentiation, and I have given in the following pages what I conceive to be good reasons for so thinking. And I hope that the fact of the explanations there offered running counter to the traditional one will not prevent readers weighing with the utmost care the proofs that are offered.