The uninitiated regards the philosophic treatment of a theme as difficult solely by reason of its technical terms. “If I only understood your use of words, I think I should find no difficulty in your thought.” He supposes that under those bizarre terms there lurks only the meaning that he and others put into ordinary phrases. He does not seem to think that the concepts likewise are new. It is just as though an Indian were to say to the carpenter, “I could make as good work as you, if I only had the secret of using my finger-nails and teeth as you do the plane and saw.” Speculative philosophy—it cannot be too early inculcated—does _not_ “conceal under cumbrous terminology views which men ordinarily hold.” The ordinary reflection would say that Being is the ground of thought, while speculative philosophy would say that thought is the ground of Being; whether of other being, or of itself as being—for it is _causa sui_. Let us now address ourselves to the task of elaborating our technique—the tools of thought—and see what new worlds become accessible through our mental telescopes and microscopes, our analytical scalpels and psychological plummets. I.—A PRIORI AND A POSTERIORI. _A priori_, as applied to knowledge, signifies that which belongs to the nature of the mind itself. Knowledge which is before experience, or not dependent on it, is _a priori_. _A posteriori_ or _empirical_ knowledge is derived from experience. A criterion to be applied in order to test the application of these categories to any knowledge in question, is to be found in _universality_ and _necessity_. If the truth expressed has universal and necessary validity it must be _a priori_, for it could not have been derived from experience. Of empirical knowledge we can only say: “It is true so far as experience has extended.” Of _a priori_ knowledge, on the contrary, we affirm: “It is universally and necessarily true and no experience of its opposite can possibly occur; from the very nature of things it must be so.” II.—ANALYTICAL AND SYNTHETICAL. A judgment which, in the predicate, adds nothing new to the subject, is said to be _analytical_, as e. g. “Horse is an animal;”—the concept “animal” is already contained in that of “horse.” _Synthetical_ judgments, on the contrary, add in the predicate something new to the conception of the subject, as e. g. “This rose is red,” or “The shortest distance between two points is a straight line;”—in the first judgment we have “red” added to the general concept “rose;” while in the second example we have _straightness_, which is quality, added to _shortest_, which is quantity. III.—APODEICTICAL.