A Commentary to Kant's 'Critique of Pure Reason'

by Norman Kemp Smith

The whole matter is, however, still further complicated by the distinction, which we have already noted, between real and ideal possibility. Are the given synthetic a priori judgments valid? That is one question. Can the Critical philosophy discover, completely enumerate, and prove in a manner never before done, all the possible synthetic a priori principles? That is a very different problem, and when raised brings us to the further discussion of Kant’s transcendental method. The question at issue is no longer merely whether or not certain given judgments are valid, and how, if valid, they are to be accounted for. The question is now that of discovering and of proving principles which have not been established by any of the special sciences. This shifting of the problem is concealed from Kant himself by his omission to distinguish between the undemonstrated axioms of the mathematical sciences and their derivative theorems, between the principles employed by the physicist without enquiry into their validity and the special laws based upon empirical evidence.

As regards the mathematical axioms, the problem is fairly simple. As we shall see later, in the Aesthetic, they do not require a deduction in the strict transcendental sense. They really fall outside the application of the transcendental method. They require only an “exposition.” But in regard to the fundamental principles of natural science we are presented with the problem of discovery as well as of proof. Unlike the axioms of the mathematician, they are frequently left unformulated. And many postulates, such as that there is a lex continui in natura, are current in general thought, and claim equal validity with the causal principle. Kant has thus to face the question whether in addition to those principles employed more or less explicitly by the scientist, others, such as might go to form an immanent metaphysics of nature, may not also be possible.

B. (a)[185] Psychological and logical possibility.—Both have to be recognised and accounted for. Let us consider each in order.

(1) Psychological possibility.—What are the subjective conditions of a priori synthetic judgments? Through what mental faculties are they rendered possible? Kant replies by developing what may be called a transcendental psychology. They depend upon space and time as forms of sensibility, upon the a priori concepts of understanding, and upon the synthetic activities by which the imagination schematises these concepts and reduces the given manifold to the unity of apperception. This transcendental psychology is the necessary complement of the more purely epistemological analysis.[186] But on this point Kant’s utterances are extremely misleading. His Critical enquiry has, he declares, nothing in common with psychology. In the Preface to the first edition we find the following passage: “This enquiry ... [into] the pure understanding itself, its possibility and the cognitive faculties upon which it rests ..., although of great importance for my chief purpose, does not form an essential part of it.”[187] The question, he adds, “how is the faculty of thought itself possible?... is as it were a search for the cause of a given effect, and therefore is of the nature of an hypothesis [or ‘mere opinion’], though, as I shall show elsewhere, this is not really so.” The concluding words of this passage very fairly express Kant’s hesitating and inconsistent procedure. Though he has so explicitly eliminated from the central enquiry of the Critique all psychological determination of the mental powers, statements as to their constitution are none the less implied, and are involved in his epistemological justification alike of a priori knowledge and of ordinary experience. If we bear in mind that Kant is here attempting to outline the possible causes of given effects, and that his conclusions are therefore necessarily of a more hypothetical character than those obtained by logical analysis, we shall be prepared to allow him considerable liberty in their formulation. But in certain respects his statements are precise and definite—the view, for instance, of sensations as non-spatial, of time as a form of inner sense, of the productive imagination as pre-conditioning our consciousness, of spontaneity as radically distinct from receptivity, of the pure forms of thought as not acquired through sense, etc. No interpretation which ignores or under-estimates this psychological or subjective aspect of his teaching can be admitted as adequate.[188]

(2) Logical or epistemological possibility.—How can synthetic a priori judgments be valid? This question itself involves a twofold problem. How, despite their synthetic character, can they possess truth, i.e. how can we pass from their subject terms to their predicates? And secondly, how, in view of their origin in our human reason, can they be objectively valid, i.e. legislate for the independently real? How can we pass beyond the subject-predicate relation to real things? This latter is the Critical problem in the form in which it appears in Kant’s letter of 1772 to Herz.[189] The former is the problem of synthesis which was later discovered.

(b) (1) Possibility of explanation and (2) possibility of existence.—(1) How can synthetic a priori judgments be accounted for? How, despite their seemingly inconsistent and apparently paradoxical aspects, can their validity (their validity as well as their actuality being taken for granted) be rendered comprehensible? (2) The validity of such judgments has been called in question by the empiricists, and is likewise inexplicable even from the dogmatic standpoint of the rationalists. How, then, can these judgments be possible at all? These two meanings of the term ‘possible’ connect with the ambiguity, above noted, in the term ‘how.’ The former problem can be solved by an analytic method; the latter demands the application of the more radical method of synthetic reconstruction.

(c) Real and ideal possibility.[190]—We have to distinguish between the possible validity of those propositions which the mathematical and physical sciences profess to have established and the possible validity of those principles such as that of causality, which are postulated by the sciences, but which the sciences do not attempt to prove, and which in certain cases they do not even formulate. The former constitute an actually existent body of scientific knowledge, demonstrated in accordance with the demands of scientific method. The latter are employed by the scientist, but are not investigated by him. The science into which they can be fitted has still to be created; and though some of the principles composing it may be known, others remain to be discovered. All of them demand such proof and demonstration as they have never yet received.[191] This new and ideal science is the scientific metaphysics which Kant professes to inaugurate by means of the Critique. In reference to the special sciences, possibility means the conditions of the actually given. In reference to the new and ideal metaphysics, possibility signifies the conditions of the realisation of that which is sought. In view of this distinction, the formula—How are synthetic a priori judgments possible?—will thus acquire two very different meanings. (1) How are the existing a priori synthetic judgments to be accounted for? (2) How may all the really fundamental judgments of that type be exhaustively discovered and proved? Even in regard to immanent metaphysics Kant interprets the formula in both ways. This is due to his frequent confusion of immanent metaphysics with the principles of natural science. Its propositions are then regarded as given, and only their general validity calls for proof. It is, however, in the problem of ideal possibility that the essential problem of the Critique lies; and that is a further reason why it cannot be adequately dealt with, save by means of the synthetic method.

Experience.—Throughout the Introduction the term experience[192] has (even at times in one and the same sentence) two quite distinct meanings, (1) as product of sense and understanding acting co-operatively, and (2) as the raw material (the impressions) of sense. Considerable confusion is thereby caused.

Understanding and reason[193] are here, as often elsewhere in the Critique, used as equivalent terms. Throughout the entire two first sections of the Introduction to the second edition the term reason does not occur even once. As first mentioned,[194] it is taken as the source of metaphysical judgments.

General (a priori) truths have an inner necessity and must be clear and certain by themselves.[195]—These statements are not in accordance with Kant’s new Critical teaching.[196] They have remained uncorrected from a previous way of thinking. This must be one reason for the recasting of this paragraph in the second edition.