But let me gather up in a few words the purport of what has been said above. Philosophy once meant the whole body of scientific knowledge. Afterward it came to mean the whole body of knowledge which could be attained by the mere light of human reason, unaided by revelation. The several special sciences sprang up, and a multitude of men have for a long time past devoted themselves to definite limited fields of investigation with little attention to what has been done in other fields. Nevertheless, there has persisted the notion of a discipline which somehow concerns itself with the whole system of things, rather than with any limited division of that broad field. It is a notion not peculiar to the disciples of Spencer. There are many to whom philosophy is a "Weltweisheit," a world-wisdom. Shall we say that this is the meaning of the word philosophy now? And if we do, how shall we draw a line between philosophy and the body of the special sciences?
Perhaps the most just way to get a preliminary idea of what philosophy means to the men of our time is to turn away for the time being from the definition of any one man or group of men, and to ask ourselves what a professor of philosophy in an American or European university is actually supposed to teach.
It is quite clear that he is not supposed to be an Aristotle. He does not represent all the sciences, and no one expects him to lecture on mathematics, mechanics, physics, chemistry, zoölogy, botany, economics, politics, and various other disciplines. There was a time when he might have been expected to teach all that men could know, but that time is long past.
Nevertheless, there is quite a group of sciences which are regarded as belonging especially to his province; and although a man may devote a large part of his attention to some one portion of the field, he would certainly be thought remiss if he wholly neglected the rest. This group of sciences includes logic, psychology, ethics and aesthetics, metaphysics, and the history of philosophy. I have not included epistemology or the "theory of knowledge" as a separate discipline, for reasons which will appear later (Chapter XIX); and I have included the history of philosophy, because, whether we care to call this a special science or not, it constitutes a very important part of the work of the teacher of philosophy in our day.
Of this group of subjects the student who goes to the university to study philosophy is supposed to know something before he leaves its walls, whatever else he may or may not know.
It should be remarked, again, that there is commonly supposed to be a peculiarly close relation between philosophy and religion. Certainly, if any one about a university undertakes to give a course of lectures on theism, it is much more apt to be the professor of philosophy than the professor of mathematics or of chemistry. The man who has written an "Introduction to Philosophy," a "Psychology," a "Logic," and an "Outlines of Metaphysics" is very apt to regard it as his duty to add to the list a "Philosophy of Religion." The students in the theological seminaries of Europe and America are usually encouraged, if not compelled, to attend courses in philosophy.
Finally, it appears to be definitely accepted that even the disciplines that we never think of classing among the philosophical sciences are not wholly cut off from a connection with philosophy. When we are occupied, not with adding to the stock of knowledge embraced within the sphere of any special science, but with an examination of the methods of the science, with, so to speak, a criticism of the foundations upon which the science rests, our work is generally recognized as philosophical. It strikes no one as odd in our day that there should be established a "Journal of Philosophy, Psychology, and Scientific Methods," but we should think it strange if some one announced the intention to publish a "Journal of Philosophy and Comparative Anatomy." It is not without its significance that, when Mach, who had been professor of physics at Prague, was called (in 1895) to the University of Vienna to lecture on the history and theory of the inductive sciences, he was made, not professor of physics, but professor of philosophy.
The case, then, stands thus: a certain group of disciplines is regarded as falling peculiarly within the province of the professor of philosophy, and the sciences which constitute it are frequently called the philosophical sciences; moreover, it is regarded as quite proper that the teacher of philosophy should concern himself with the problems of religion, and should pry into the methods and fundamental assumptions of special sciences in all of which it is impossible that he should be an adept. The question naturally arises: Why has his task come to be circumscribed as it is? Why should he teach just these things and no others?
To this question certain persons are at once ready to give an answer. There was a time, they argue, when it seemed possible for one man to embrace the whole field of human knowledge. But human knowledge grew; the special sciences were born; each concerned itself with a definite class of facts and developed its own methods. It became possible and necessary for a man to be, not a scientist at large, but a chemist, a physicist, a biologist, an economist. But in certain portions of the great field men have met with peculiar difficulties; here it cannot be said that we have sciences, but rather that we have attempts at science. The philosopher is the man to whom is committed what is left when we have taken away what has been definitely established or is undergoing investigation according to approved scientific methods. He is Lord of the Uncleared Ground, and may wander through it in his compassless, irresponsible way, never feeling that he is lost, for he has never had any definite bearings to lose.
Those who argue in this way support their case by pointing to the lack of a general consensus of opinion which obtains in many parts of the field which the philosopher regards as his own; and also by pointing out that, even within this field, there is a growing tendency on the part of certain sciences to separate themselves from philosophy and become independent. Thus the psychologist and the logician are sometimes very anxious to have it understood that they belong among the scientists and not among the philosophers.