made them realists, and not the particular sort of nature which they regarded as real. The changeless, although sensuous and materialistic Being of the Eleatics, is only one case of such sharp sundering of the real from the seeming. That true Being is, in some essential way, independent of false opinion, thus comes early to be regarded as a sort of obvious maxim. When Protagoras attacks this maxim, his extreme form of expression is a natural reaction from another extreme. Plato’s theory of the incorporeal Ideas, in its more extreme form, rests upon the presupposition, that unless knowledge is founded upon the absolutely independent reality, nothing is known.[1] Aristotle, in his Metaphysics, spends a long time in trying to define what makes any real object, or substance, just itself, — a being logically independent of other beings. That the definition of this essence or of any being also implies that a real substance is independent of the accident that it is known by another is, for Aristotle, rather a tacitly assumed and self-evident matter than a topic of frequent overt argument. But when, in
- ↑ Any summary statement of the significance of the Platonic Ideas has to be, in a measure, unjust. I here follow what is, on the whole, Zeller’s interpretation; and I lay stress upon the extremer form of the Platonic theory. Plato himself sometimes saw much deeper. Independence, in the abstract sense hereafter to be defined, seems indeed certainly to be implied in the famous expression (Sympos. p. 211, A and B): αὐτὸ καθ᾽ αὑτὸ μεθ᾽ αὑτοῦ μονοειδὲς ἀεὶ ὄν, taken in its context as the climax of an effort to define the complete indifference of the Ideas to all beyond. But that the Plato of the Philebus and the Sophist recognizes other aspects of the situation is true. The argument (Sophist, p. 248) that our knowledge of Being is one of the proofs that the Real is both active and passive, and enters into relations, is identical in spirit with the criticism of Realism here to be given.
