These definitions which we have selected to record and to interpret (and others which we leave to the reader to record and to interpret) are all _formal,_ in the legitimate sense of the word. They define the eternal nature of philosophy, they do not determine actually any special solution of other philosophical problems, although naturally they do potentially determine one solution, in that they can agree only with one solution. Obedient to this formal character, we have not taken and shall not take account of definitions that imply the effective solution of all philosophical problems, or of Philosophy in its totality. Such is, for instance, the definition that Philosophy is knowledge of oneself, as was said at the dawn of Hellenic thought; or that it is the return to the inward man where dwells the truth, as St. Augustine said; or that it is the science of Spirit, as we say. This definition offers something more than the simply logical aspect of Philosophy. Looked at from the purely logical standpoint, Philosophy will be the science of God or of the Devil, of Spirit or Matter, of final cause or mechanism, or of anything else that may be suggested as a hypothesis for enquiry, provided that this, whatever it be, is thinkable as a _pure concept or Idea._ Whoever should negate this condition, would not negate this or that philosophy, but as we have seen, philosophy itself, in favour of art, of action, or of something else. [Sidenote: _Idealism of every philosophy._] But if Philosophy is by its logical nature pure concept or idea, every philosophy, to whatever results it may attain, and whatever may be its errors, is in its essential character and deepest tendency, _idealism._ This has been recognized by philosophers of the most different and antagonistic views (for example, by Hegel and by Herbart). It should be taught as truth to those who are ignorant of it and those who have forgotten should be reminded of it. Determinism negates the end and affirms the cause; but the cause which it posits as its principle, is not this or that cause, but the _idea_ of cause. Materialism negates thought and affirms matter; but not this or that matter, which composes this or that body, but the _idea_ of matter. Naturalism denies spirit and affirms nature; not this or that manifestation of nature, but nature as _idea._ Finally, when a single natural fact seems to be posited as the principle of explanation of reality, this fact is idealized and stands as the idea of itself, generating itself and everything else. Thus (it has been repeatedly remarked) the water of Thales, by the very fact that it is taken as a principle, is no longer any given empirical water, but metaphysical and ideal water. In like manner, the _numbers_ of Pythagoras are not those of the Pythagorean table, but cosmic principles and ideas. Theism does not believe it possible to obtain the sufficient reason of reality, without positing a personal God, above and beyond the world. But this God is