Hume / (English Men of Letters Series)

by Thomas Henry Huxley

But though, by reason of the special purpose of philosophy, its distinctness from other branches of scientific investigation may be properly vindicated, it is easy to see that, from the nature of its subject-matter, it is intimately and, indeed, inseparably connected with one branch of science. For it is obviously impossible to answer the question, What can we know? unless, in the first place, there is a clear understanding as to what is meant by knowledge; and, having settled this point, the next step is to inquire how we come by that which we allow to be knowledge; for, upon the reply, turns the answer to the further question, whether, from the nature of the case, there are limits to the knowable or not. While, finally, inasmuch as What can I know? not only refers to knowledge of the past or of the present, but to the confident expectation which we call knowledge of the future; it is necessary to ask, further, what justification can be alleged for trusting to the guidance of our expectations in practical conduct.

It surely needs no argumentation to show, that the first problem cannot be approached without the examination of the contents of the mind; and the determination of how much of these contents may be called knowledge. Nor can the second problem be dealt with in any other fashion; for it is only by the observation of the growth of knowledge that we can rationally hope to discover how knowledge grows. But the solution of the third problem simply involves the discussion of the data obtained by the investigation of the foregoing two.

Thus, in order to answer three out of the four subordinate questions into which What can I know? breaks up, we must have recourse to that investigation of mental phenomena, the results of which are embodied in the science of psychology.

Psychology is a part of the science of life or biology, which differs from the other branches of that science, merely in so far as it deals with the psychical, instead of the physical, phenomena of life.

As there is an anatomy of the body, so there is an anatomy of the mind; the psychologist dissects mental phenomena into elementary states of consciousness, as the anatomist resolves limbs into tissues, and tissues into cells. The one traces the development of complex organs from simple rudiments; the other follows the building up of complex conceptions out of simpler constituents of thought. As the physiologist inquires into the way in which the so-called "functions" of the body are performed, so the psychologist studies the so-called "faculties" of the mind. Even a cursory attention to the ways and works of the lower animals suggests a comparative anatomy and physiology of the mind; and the doctrine of evolution presses for application as much in the one field as in the other.

But there is more than a parallel, there is a close and intimate connexion between psychology and physiology. No one doubts that, at any rate, some mental states are dependent for their existence on the performance of the functions of particular bodily organs. There is no seeing without eyes, and no hearing without ears. If the origin of the contents of the mind is truly a philosophical problem, then the philosopher who attempts to deal with that problem, without acquainting himself with the physiology of sensation, has no more intelligent conception of his business than the physiologist, who thinks he can discuss locomotion, without an acquaintance with the principles of mechanics; or respiration, without some tincture of chemistry.

On whatever ground we term physiology, science, psychology is entitled to the same appellation; and the method of investigation which elucidates the true relations of the one set of phenomena will discover those of the other. Hence, as philosophy is, in great measure, the exponent of the logical consequences of certain data established by psychology; and as psychology itself differs from physical science only in the nature of its subject-matter, and not in its method of investigation, it would seem to be an obvious conclusion, that philosophers are likely to be successful in their inquiries, in proportion as they are familiar with the application of scientific method to less abstruse subjects; just as it seems to require no elaborate demonstration, that an astronomer, who wishes to comprehend the solar system, would do well to acquire a preliminary acquaintance with the elements of physics. And it is accordant with this presumption, that the men who have made the most important positive additions to philosophy, such as Descartes, Spinoza, and Kant, not to mention more recent examples, have been deeply imbued with the spirit of physical science; and, in some cases, such as those of Descartes and Kant, have been largely acquainted with its details. On the other hand, the founder of Positivism no less admirably illustrates the connexion of scientific incapacity with philosophical incompetence. In truth, the laboratory is the fore-court of the temple of philosophy; and whoso has not offered sacrifices and undergone purification there, has little chance of admission into the sanctuary.

Obvious as these considerations may appear to be, it would be wrong to ignore the fact that their force is by no means universally admitted. On the contrary, the necessity for a proper psychological and physiological training to the student of philosophy is denied, on the one hand, by the "pure metaphysicians," who attempt to base the theory of knowing upon supposed necessary and universal truths, and assert that scientific observation is impossible unless such truths are already known or implied: which, to those who are not "pure metaphysicians," seems very much as if one should say that the fall of a stone cannot be observed, unless the law of gravitation is already in the mind of the observer.

On the other hand, the Positivists, so far as they accept the teachings of their master, roundly assert, at any rate in words, that observation of the mind is a thing inherently impossible in itself, and that psychology is a chimera—a phantasm generated by the fermentation of the dregs of theology. Nevertheless, if M. Comte had been asked what he meant by "physiologic cérebrale," except that which other people call "psychology;" and how he knew anything about the functions of the brain, except by that very "observation intérieure," which he declares to be an absurdity—it seems probable that he would have found it hard to escape the admission, that, in vilipending psychology, he had been propounding solemn nonsense.

It is assuredly one of Hume's greatest merits that he clearly recognised the fact that philosophy is based upon psychology; and that the inquiry into the contents and the operations of the mind must be conducted upon the same principles as a physical investigation, if what he calls the "moral philosopher" would attain results of as firm and definite a character as those which reward the "natural philosopher."[14] The title of his first work, a "Treatise of Human Nature, being an Attempt to introduce the Experimental method of Reasoning into Moral Subjects," sufficiently indicates the point of view from which Hume regarded philosophical problems; and he tells us in the preface, that his object has been to promote the construction of a "science of man."