Stewart, in his criticism of Kant's doctrines, remarks that, in asserting that the human mind possesses, in its own ideas, an element of necessary and universal truth, not derived from experience, Kant had been anticipated by Price, by Cudworth, and even by Plato; to whose _Theætetus_ both Price and Cudworth refer, as containing views similar to their own. And undoubtedly this doctrine of ideas, as indispensable sources of necessary truths, was promulgated and supported by weighty arguments in the _Theætetus_; and has ever since been held by many philosophers, in opposition to the contrary doctrine, also extensively held, that all truth is derived from experience. But, in pointing out this circumstance as diminishing the importance of Kant's speculations, Stewart did not sufficiently consider that doctrines, fundamentally the same, may discharge a very different office at different periods of the history of philosophy. Plato's Dialogues did not destroy, nor even diminish, the value of Cudworth's "Immutable Morality." Notwithstanding Cudworth's publications, Price's doctrines came out a little afterwards with the air and with the effect of novelties. Cudworth's assertion of ideas did not prevent the rise of Hume's skepticism; and it was Hume's skepticism which gave occasion to Kant's new assertion of necessary and universal truth, and to his examination into the grounds of the possibility and reality of such truth. To maintain such doctrine _after_ the appearance of intermediate speculations, and with reference to them, was very different from maintaining it before; and this is the merit which Kant's admirers claim for him. Nor can it be denied that his writings produced an immense effect upon the mode of treating such questions in Germany; and have had, even in this country, an influence far beyond what Mr. Stewart would have deemed their due.