Plato calls the Ideas are of such nature as to be truly and eternally independent realities, and on the other hand, that the Ideas, while thus independently real, are to be so defined as to explain the universality of knowledge, and the eternal validity of truth. The Platonic Ideas were therefore realistic entities, in the sense of our first conception of what it is to be. They constituted an incorporeal world of independent realities. But the arguments used for their reality, and the relations which they bore to ethical and to other permanent truths, as well as the fact that they corresponded, not to our individual but to our universal conceptions, gave them characters which inevitably led them, in the later Platonic tradition, to assume forms more and more similar, either to beings of the type now in question, or to the sort of Being yet to be defined by our Fourth Conception of Reality, and hereafter to be treated. The Neo-Platonic doctrine identified the Platonic Ideas with the thoughts of the divine Intelligence. St. Augustine, in a proof of God’s existence, identified God with Veritas. St. Thomas, in explaining the relation of the Ideas to God, was led to an interesting form of our present or Third Conception of Being; and post-Kantian idealism has remodelled the Platonic Ideas, on the whole, after the plan first suggested by the Neo-Platonic doctrine. In brief, then, Plato’s concept of Being, while technically realistic, contains tendencies that inevitably lead to the differentiation of other ontological conceptions. And so our present or Third Conception of Being is, in large part, indirectly due to Plato.
Nearer to our present form of the ontological predi-
