Philosophy is an investigation of the first principles of unman knowledge. It seeks an answer to such questions as these: Are there any propositions of the truth of which we can be certain ? How is their truth to be tested - by an appeal to "experience," or by ascertaining their agreement with certain "forms" inherent in the mind itself? If nothing is found to be certain, then we get the doctrine of philosophical scepticism. If one of the other positions is taken, we have respectively philosophical experientialism or rationalism. Having found what makes knowledge valid, the philosopher goes on to determine, with more or less completeness, what is to be thought about the whole of things. The sciences deal only with the parts, and take for granted various assumptions. Philosophy examines the assumptions, distinguishes appearance - from reality, re-states the results of science in accordance with this distinction, and brings the parts into a system. In this way philosophy becomes metaphysics. This is the course it now takes: first, critical examination of knowledge, then speculative construction. Historically, the process was the opposite.
Philosophy began as a theory of the universe. The philosopher did not first try to discover whether anything can be known, and if so what can be known; but, trusting to the mind's powers, laid down some principle as certain, and proceeded to explain everything by means of it. Philosophy was not then distinguished from special science, but included science in itself. The sciences have gradually become separate, as it has been found possible or necessary to treat aspects of things apart from the whole, philosophy retaining for itself the theory of the whole and the criticism of scientific assumptions. When philosophers began with untested general principles the notion was that these, as soon as stated, were obvious. It was found, however, that different philosophers took different starting-points, and that the theories of the universe attained were quite different and even incompatible with each other. From the perception of this sprang, first, assertions that nothing could be known, then attempts at reasoned selection of true principles. It was seen that only when comparison had been made among principles was genuine philosophical construction possible. This historical movement has not taken place once for all, but has been frequently repeated. Constructive periods and critical periods have alternated, but the general result has been that critical investigation of knowledge has had to become constantly severer and more systematic. This has meant that philosophers have had to turn more and more to investigation of the mind's powers. Philosophy has thus acquired a special association with mental as distinguished from natural science. So far, only theoretical philosophy has been spoken of, but philosophy has also its practical department. Not only have we to distinguish true from apparent knowledge; we also have to learn what objects of desire are good, and what modes of action are right. Where disputes arise as to which of the various modes of action that men spontaneously adopt are directed to the proper end, or are according to the true rule, these differences have to be brought to the test of practical philosophy. Theoretical knowledge of the universe and of men in their relations to one another has to be followed by practical directions to choose certain ends, or to act according to certain rules. All knowledge has to be brought into relation with these, so as to make clear what means must be taken for attaining the ends, or for applying the general rules to particular circumstances. Thus philosophy includes ethics as well as metaphysics. It also includes aesthetics, the object of which is to discover why certain things in nature and in art are considered beautiful, to determine what really constitutes beauty, how this can be known, and how it can be realised. Philosophy, theoretical and practical, has appeared in all civilisations that have reached the stage of reflecting upon the world and upon themselves. European philosophy began in Greece about the seventh or sixth century B.C. From then till now it has been cultivated with very different degrees of zeal and of success in different ages and countries; but during the whole period of more than two thousand years it has a history that has never been absolutely broken.