We reach them through the doorways of the Necessary _vs._ the Contingent, the Unconditioned _vs._ the Conditioned, the Infinite _vs._ the Finite, the Absolute _vs._ the Relative; and we recognize them as our profoundest foundation-concepts, alone deserving, as Kant so pertinently said, the name of IDEAS,--the Soul, the World, and God. Associated with them are what we may call our three Forms of the Ideal,--the True, the Beautiful, the Good. These Ideas and their affiliated ideals have the highest directive and settling function in the organization of philosophy; they determine its schools and its history, by forming the centre of all its controlling problems; they prescribe its great subdivisions, breaking it up into Metaphysics, Æsthetics, and Ethics, and Metaphysics, again, into Psychology Cosmology, and Ontology,--or Theology in the classic sense, which, in the modern sense, becomes the Philosophy of Religion; they call into existence, as essential preparatory and auxiliary disciplines, Logic and the Theory of Knowledge, or Epistemology. They thus provide the true distinctions between philosophy and the sciences of experience, and present these sciences as the carrying out, upon experiential details, of the methodological principles which philosophy alone can supply; hence they lead us to view all the sciences as in fact the applied branches, the completing organs of philosophy, instead of its hostile competitors. As for the controlling questions which they start, these are such as follow: Are the ideals but bare ideals, serving only to cast "a light that never was, on land or sea?"--are the Ideas only bare ideas, without any objective being of their own, without any footing in the real, serving only to enhance the dull facts of experience with auroral illusions? The philosophic thinker answers affirmatively, or with complete skeptical dubiety, or with a convinced and uplifting negative, according to his less or greater penetration into the real meaning of these deepest concepts, and depending on his view into the nature and thought-effect of the Necessary and the Contingent, the Unconditioned and the Conditioned, the Infinite and the Finite, the Absolute and the Relative.