This argument, then, of Plato against the Idealists is an argument against the Absolute--showing that there can be no Object of intelligence or conception without its obverse side, the intelligent or concipient Subject. The Idealists held, that by soaring above the sensible world into the intelligible world, they got out of the region of the Relative into that of the Absolute. But Plato reminds them that this is not the fact. Their intelligible world is relative, not less than the sensible; that is, it exists only in communion with a mind or Subject, but with a Cogitant or intelligent Subject, not a percipient Subject. [Side-note: Coincidence of his argument with the doctrine of Protagoras in the Theætêtus.] The argument here urged by Plato coincides in its drift and result with the dictum of Protagoras--Man is the measure of all things. In my remarks on the Theætêtus,[107] I endeavoured to make it appear that the Protagorean dictum was really a negation of the Absolute, of the Thing in itself, of the Object without a Subject:--and an affirmation of the Relative, of the Thing in communion with a percipient or concipient mind, of Object implicated with Subject--as two aspects or sides of one and the same conception or cognition. Though Plato in the Theætêtus argued at length against Protagoras, yet his reasoning here in the Sophistês establishes by implication the conclusion of Protagoras. Here Plato impugns the doctrine of those who (like Sokrates in his own Theætêtus) held that the sensible world alone was relative, but that the intelligible world or Forms were absolute. He shows that the latter were no less relative to a mind than the former; and that mind, either percipient or cogitant, could never be eliminated from "communion" with them. [Footnote 107: See my notice of the Theætêtus, in the chapter immediately preceding, where I have adverted to Plato's reasoning in the Sophistês.] [Side-note: The Idealists maintained that Ideas or Forms were entirely unchangeable and eternal. Plato here denies this, and maintains that ideas were partly changeable, partly unchangeable.]