This is a list of Gordon Clark quotes about Plato and Rationalism. For each quote, there is a link where you can purchase the book where the quote came from.
Gordon Clark Refutes Plato (Wheaton Lectures)
From Clark and His Critics, published by the Trinity Foundation (page numbers are from the Apple Books e-book).
Plato, however, seems to have escaped the artificialities of the Hegelian dialectic. Plato held that the objects of knowledge, constituting the real world in distinction to the half-unreal world of sensation, were suprasensible, unchangeable Ideas. Not only do they furnish the contents of mathematics and account for teleology in nature, what is more important, they give us the norms of ethics and politics. Unlike the ease with which much Hegelianism is refuted, the standard objections to the Ideas, objections that Plato himself clearly stated in the Parmenides, cannot be regarded as unanswerable. On one major base some sort of theory of Ideas stands impregnable. It is the necessity of similarities and classifications. Unless we can use concepts and talk of groups of things, philosophy would be impossible. If only individual things existed, and every noun were a proper name, conversation and even thinking itself could not be carried on. Neither the medieval nominalists nor Bishop Berkeley, who tried to get along without abstract ideas, was able to explain the reason why we classify men as men and horses as horses. Classification requires Ideas, and zoology requires classification. So does mathematics. Cubes vary infinitely in size, but they all have the same identical shape. Not only are there ellipses and parabolas, but there is also an invisible, eternal, unchangeable general conic. Theology, too, uses the classes Jew and Gentile, saint and sinner, not to mention God and man. All thought and speech depend on classification, and no epistemology can succeed without something like the Platonic Ideas.
Furthermore, when Plato confines himself to mathematical examples, like the Idea of Equality, his theory of reminiscence, by which he tries to explain how we come to know the Ideas, is quite attractive. Since it is impossible to abstract mathematical concepts from experience, for neither the perfect cube nor the general conic is ever found in experience, why may we not have been born omniscient and learn by remembering the eternal world from which we fell?
But though there may be Ideas of some sort, when Plato leaves mathematics for politics the plausibility of reminiscence vanishes. The slave boy was easily able to remember the square on the diagonal, but neither the Athenians nor the Syracusans could remember justice, not even with the lengthy stimulus of the Republic.
Justice, of course, is a matter of ethics and politics; and more will be said about ethics later. But the definition of man as a two-legged animal without feathers is another case where reminiscence did not work too well. The difficulty is that, after one grants the existence of suprasensible Ideas, sensation stimulates different notions in different people. Whether the subject be justice or piety or the planetary spheres, Plato had to rely on procedures of ethics and science which cannot be completed.
The failure of Platonism to descend from Heaven to Earth, or, if you wish, to ascend from Earth to Heaven, leaves the theory ineffective. Man before birth may have been omniscient, but here below the Platonic cave in which man is a prisoner actually has no opening. Platonism therefore cannot be accepted as the solution to our problem.Gordon H. Clark. “Clark and His Critics.” Apple Books. 49-52.