It is therefore certain, that, in the true Platonic theory, Ideas are not beings in the vulgar sense of the word, beings which would be neither in the mind of man, nor in nature, nor in God, and would subsist only by themselves. No, Plato considers Ideas as being at once the principles of sensible things, of which they are the laws, and the principles also of human knowledge, which owes to them its light, its rule, and its end, and the essential attributes of God, that is to say, God himself.
Plato is truly the father of the doctrine which we have explained, and the great philosophers who have attached themselves to his school have always professed this same doctrine.
The founder of Christian metaphysics, St. Augustine, is a declared disciple of Plato: everywhere he speaks, like Plato, of the relation of human reason to the divine reason, and of truth to God. In the City of God, book x., chap. ii., and in chap. ix. of book vii. of the Confessions, he goes to the extent of comparing the Platonic doctrine with that of St. John.
He adopts, without reserve, the theory of Ideas. Book of Eighty-three Questions, question 46: "Ideas are the primordial forms, and, as it were, the immutable reasons of things; they are not created, they are eternal, and always the same: they are contained in the divine intelligence; and without being subject to birth and death, they are the types according to which is formed every thing that is born and dies."[54]
"What man, pious, and penetrated with true religion, would dare to deny that all things that exist, that is to say, all things that, each of its kind, possess a determinate nature, have been created by God? This point being once conceded, can it be said that God has created things without reason? If it is impossible to say or think this, it follows that all things have been created with reason. But the reason of the existence of a man cannot be the same as the reason of the existence of a horse; that is absurd; each thing has therefore been created by virtue of a reason that is peculiar to it. Now, where can these reasons be, except in the mind of the Creator? For he saw nothing out of himself, which he could use as a model for creating what he created: such an opinion would be sacrilege.[55]
"If the reasons of things to be created and things created are contained in the divine intelligence, and if there is nothing in the divine intelligence but the eternal and immutable, the reasons of things which Plato calls Ideas, are the eternal and immutable truths, by the participation in which every thing that is is such as it is."[56]
St. Thomas himself, who scarcely knew Plato, and who was often enough held by Aristotle in a kind of empiricism, carried away by Christianity and St. Augustine, let the sentiment escape him, "that our natural reason is a sort of participation in the divine reason, that to this we owe our knowledge and our judgments, that this is the reason why it is said, that we see every thing in God."[57] There are in St. Thomas many other similar passages, of perhaps an expressive Platonism, which is not the Platonism of Plato, but of the Alexandrians.
The Cartesian philosophy, in spite of its profound originality, and its wholly French character, is full of the Platonic spirit. Descartes has no thought of Plato, whom apparently he has never read; in nothing does he imitate or resemble him: nevertheless, from the first, he is met in the same regions with Plato, whither he goes by a different route.
The notion of the infinite and the perfect is for Descartes what the universal, the Idea, is for Plato. No sooner has Descartes found by consciousness that he thinks, than he concludes from this that he exists, then, in course, by consciousness still, he recognizes himself as imperfect, full of defects, limitations, miseries, and, at the same time, conceives something infinite and perfect. He possesses the idea of the infinite and the perfect; but this idea is not his own work, for he is imperfect; it must then have been put into him by another being endowed with perfection, whom he conceives, whom he does not possess:—that being is God. Such is the process by which Descartes, setting out from his own thought, and his own being, elevated himself to God. This process, so simple, which he so simply exposes in the Discours de la Méthode, he will put successively, in the Méditations, in the Résponses aux Objections, in the Principes, under the most diverse forms, he will accommodate it, if it is necessary, to the language of the schools, in order that it may penetrate into them. After all, this process is compelled to conclude, from the idea of the infinite and the perfect, in the existence of a cause of this idea, adequate, at least, to the idea itself, that is to say, infinite and perfect. One sees that the first difference between Plato and Descartes is, that the ideas which in Plato are at once conceptions of our mind, and the principles of things, are for Descartes, as well as for all modern philosophy, only our conceptions, amongst which that of the infinite and perfect occupies the first place; the second difference is, that Plato goes from ideas to God by the principle of substances, if we may be allowed to use this technical language of modern philosophy; whilst Descartes employs rather the principle of causality, and concludes—well understood without syllogism—from the idea of the infinite and the perfect in a cause also perfect and infinite.[58] But under these differences, and in spite of many more, is a common basis, a genius the same, which at first elevates us above the senses, and, by the intermediary of marvellous ideas that are incontestably in us, bears us towards him who alone can be their substance, who is the infinite and perfect author of our idea of infinity and perfection. For this reason, Descartes belongs to the family of Plato and Socrates.