But the name “Idea” is very unfortunately chosen for these pretended necessary productions of the pure theoretical reason, and violently appropriated from Plato, who used it to denote the eternal forms which, multiplied through space and time, become partially visible in the innumerable individual fleeting things. Plato's “Ideas” are accordingly throughout perceptible, as indeed the word which he chose so definitely signifies, for it could only be adequately translated by means of perceptible or visible things; and Kant has appropriated it to denote that which lies so far from all possibility of perception that even abstract thought can only half attain to it. The word “Idea,” which Plato first introduced, has, moreover, since then, through two-and-twenty centuries, always retained the significance in which he used it; for not only all ancient philosophers, but also all the Scholastics, and indeed the Church Fathers and the theologians of the Middle Ages, used it only in that Platonic sense, the sense of the Latin word exemplar, as Suarez expressly mentions in his twenty-fifth Disputation, sect. 1. That Englishmen and Frenchmen were later induced by the poverty of their languages to misuse this word is bad enough, but not of importance. Kant's misuse of the word idea, by the substitution of a new significance introduced by means of the slender clue of not being object of experience, which it has in common with Plato's ideas, but also in common with every possible chimera, is thus altogether unjustifiable. Now, since the misuse of a few years is not to be considered against the authority of many centuries, I have always used the word in its old, original, Platonic significance.
The refutation of rational psychology is much fuller and more thorough in the first edition of the “Critique of Pure Reason” than in the second and following editions, and therefore upon this point we must make use of the first edition exclusively. This refutation has as a whole very great merit and much truth. Yet I am clearly of the opinion that it was merely from his love of symmetry that Kant deduced as necessary the conception of the soul from the paralogism of substantiality by applying the demand for the unconditioned to the conception substance, which is the first category of relation, and accordingly maintained that the conception of a soul arose in this way in every speculative reason. If this conception really had its origin in the presupposition of a final subject of all predicates of a thing, one would have assumed a soul not in men alone, but also just as necessarily in every lifeless thing, for such a thing also requires a final subject of all its predicates. Speaking generally, however, Kant makes use of a quite inadmissible expression when he talks of something which can exist only as subject and not as predicate (e. g., Critique of Pure Reason, p. 323; V. 412; Prolegomena, § 4 and 47); though a precedent for this is to be found in Aristotle's “Metaphysics,” iv. ch. 8. Nothing whatever exists as subject and predicate, for these expressions belong exclusively to logic, and denote the relations of abstract conceptions to each other. Now their correlative or representative in the world of perception must be substance and accident. But then we need not look further for that which exists always as substance and never as accident, but have it directly in matter. It is the substance corresponding to all properties of things which are their accidents. It is, in fact, if one wishes to retain the expression of Kant which has just been condemned, the final subject of all predicates of that empirically given thing, that which remains after the abstraction of all its properties of every kind. And this holds good of man as of a brute, a plant, or a stone, and is so evident, that in order not to see it a determined desire not to see is required. That it is really the prototype of the conception substance, I will show soon. But subject and predicate are related to substance and accident rather as the principle of sufficient reason in logic to the law of causality in nature, and the substitution or identification of the former is just as inadmissible as that of the latter. Yet in the “Prolegomena,” § 46, Kant carries this substitution and identification to its fullest extent in order to make the conception of the soul arise from that of the final subject of all predicates and from the form of the categorical syllogism. In order to discover the sophistical nature of this paragraph, one only needs to reflect that subject and predicate are purely logical determinations, which concern abstract conceptions solely and alone, and that according to their relation in the judgment. Substance and accident, on the other hand, belong to the world of perception and its apprehension in the understanding, and are even there only as identical with matter and form or quality. Of this more shortly.
The antithesis which has given occasion for the assumption of two fundamentally different