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

by Norman Kemp Smith

This irreconcilability of the subjectivist consequences of the doctrine with its realist basis was seized upon by Berkeley. To remove the contradiction, he denied the facts from which the doctrine had been developed. That is to say, starting from its results he disproved its premisses. Arguing from the physical and physiological conditions of perception Descartes had concluded that only sensations can be directly apprehended by the mind. Berkeley starts from this conclusion, and virtually adopts it as an assumption which cannot be questioned, and which does not call for proof. Since, he contends, we know only sensations, the assertion that they are due to material causes is mere hypothesis, and is one for which there may be no valid grounds. As Descartes himself had already suggested, there is a second possible method of interpreting the relevant facts. There may exist an all-powerful Being who produces the sensations in our minds from moment to moment; and provided that they are produced in the same order as now, the whole material world might be annihilated without our being in the least aware that so important an event had taken place. Since we can experience only sensations, any hypothesis which will account for the order of their happening is equally legitimate. The whole question becomes one of relative simplicity in the explanation given. The simpler analysis, other things being equal, must hold the field.

Berkeley reinforces this argument by pointing to the many embarrassing consequences to which Descartes’ dualism must lead. We postulate bodies in order to account for the origin of our sensations, and yet are unable to do so by their means. The dualistic theory creates more difficulties than it solves, without a single counter-advantage, save perhaps—so Berkeley argues—that it seems to harmonise better with the traditional prejudices of the philosophic consciousness.

If we grant Berkeley his premisses, the main lines of his argument are fairly cogent, however unconvincing may be his own positive views. The crux, however, of the Berkeleian idealism lies almost exclusively in the establishment of its fundamental assumption, that only ideas (i.e. images) can be known by the mind. This assumption Berkeley, almost without argument, takes over from his predecessors. It was currently accepted, and from it, therefore, he believed that he could safely argue. It rests, however, upon the assumption of facts which he himself questions. In rejecting the Cartesian dualism he casts down the ladder by which alone it is possible to climb into his position. For save through the facts of physics and physiology there seems to be no possible method of disproving the belief of ordinary consciousness, that in perception we apprehend independent material bodies. And until that belief can be shown to be false and ungrounded, the Berkeleian idealism is without support. It cannot establish the fundamental assumption upon which its entire argument proceeds. Thus, though Berkeley convincingly demonstrates the internal incoherence of the doctrine of representative perception—the inconsistency of its conclusions with the physical and physiological facts upon which alone it can be based—he cannot himself solve the problem in answer to which that doctrine was propounded. His services, like those of so many other reformers, were such as he did not himself foresee. In simplifying the problem, he prepared the way for the more sceptical treatment of its difficult issues by Hume.

At this point, in the philosophy of Hume, the problem of perception comes into the closest possible connection with the logical problem, referred to above. The question, how mind knowing is related to the objects known, is found to depend upon the question, how in certain crucial cases predicates may legitimately be referred to their subject. This logical problem arises in two forms, a narrower and a wider. The narrower issue concerns only the principle of causality. With what right do we assert that every event must have a cause? What is the ground which justifies us in thus predicating of events a causal character? Obviously, this logical question is fundamental, and must be answered before we can hope to solve the more special problem, as to our right to interpret sensations as effects of material bodies. Hume was the first to emphasise the vital interconnection of these two lines of enquiry.

The wider issue is the generating problem of Kant’s Critique: How in a judgment can a predicate be asserted of a subject in which it is not already involved? In other words, what is it that in such a case justifies us in connecting the predicate with the subject? Though this problem was never directly raised by any pre-Kantian thinker, not even by Hume, it is absolutely vital to all the pre-Kantian systems. Thus Descartes’ philosophy is based upon a distinction, nowhere explicitly drawn but everywhere silently assumed, between abstract and fruitful ideas. The former contain just so much content and no more; this content may be explicitly unfolded in a series of judgments, but no addition is thereby made to our knowledge. The latter, on the other hand, are endowed with an extraordinary power of inner growth. To the attentive mind they disclose a marvellous variety of inner meaning. The chief problem of scientific method consists, according to Descartes, in the discovery of these fruitful ideas, and in the separation of them from the irrelevant accompaniments which prevent them from unfolding their inner content. Once they are discovered, the steady progress of knowledge is assured. They are the springs of knowledge, and from them we have only to follow down the widening river of truth.

Descartes professed to give a complete list of the possible fruitful ideas. They are, he claimed, better known than any other concepts. They lie at the basis of all experience, and no one can possibly be ignorant of them; though, owing to their simplicity and omnipresence, their philosophical importance has been overlooked. When, however, Descartes proceeded to classify them, he found that while such ideas as space, triangle, number, motion, contain an inexhaustible content that is progressively unfolded in the mathematical sciences, those ideas, on the other hand, through which we conceive mental existences,—the notions of mind, thought, self—do not by any means prove fruitful upon attentive enquiry. As Malebranche later insisted, we can define mind only in negative terms; its whole meaning is determined through its opposition to the space-world, which alone is truly known. Though it is the function of mind to know, it cannot know itself. And when we remove from our list of ideas those which are not really fruitful, we find that only mathematical concepts remain.[1764] They alone have this apparently miraculous property of inexhaustibly developing before the mind. Scientific knowledge is limited to the material world; and even there, the limits of our mathematical insight are the limits of our knowledge.

Malebranche believed no less thoroughly than Descartes in the asserted power and fruitfulness of mathematical concepts. Under the influence of this belief, he developed, as so many other thinkers from Plato onwards have done, a highly mystical theory of scientific knowledge. It is a revelation of eternal truth, and yet is acquired by inner reflection, not laboriously built up by external observation. It comes by searching of the mind, not by exploration of the outer world. But Malebranche was not content, like Descartes, merely to accept this type of knowledge. He proceeded to account for it in metaphysical terms. The fruitfulness of mathematical ideas is due, he claimed, to the fundamental concept of extension in which they all share. This idea, representing, as it does, an infinite existence, is too great to be contained within the finite mind. Through it the mind is widened to the apprehension of something beyond itself; we know it through consciousness of its archetype in the mind of God. It is the one point at which consciousness transcends its subjective limits. Its fruitfulness is due to, and is the manifestation of, this divine source. The reason why we are condemned to remain ignorant of everything beyond the sphere of quantity is that extension alone holds this unique position. It is the only fruitful idea which the mind possesses, and other concepts, such as triangle, circle, or number, are fruitful only in proportion as they share in it. We can acquire no genuine knowledge even of the nature of the self. Being ignorant of mind, we cannot comprehend the self which is one of its modes. It is as if we sought to comprehend the nature of a triangle, in the absence of any conception of space. Were we in possession of the archetypal idea of mind, we should not only be able to deduce from it those various feelings and emotions which we have already experienced, and those sensations of the secondary qualities which we falsely ascribe to the influence of external objects, but we should also be able to discover by pure contemplation innumerable other emotions and qualities, which entirely transcend our present powers. And all of these would then be experienced in their ideal nature, and not, as now, merely through feeble and confused feeling. If mathematicians destroy their bodily health through absorption in the progressive clarification of the mysteries of space, what might not happen if the archetypal idea of mind were revealed to us? Could we attend to the preservation of a body which would incessantly distract us from the infinite and overwhelming experiences of our divine destiny?

This romantic conception of the possibilities of rational science reveals more clearly than any other Cartesian doctrine the real bearing and perverse character of the rationalistic preconceptions which underlie the Cartesian systems. The Cartesians would fain make rational science, conceived on the analogy of the mathematical disciplines, coextensive with the entire realm of the real. This grotesque enterprise is conceived as abstractly possible even by so cautious a thinker as John Locke. His reason for condemning the physical sciences as logically imperfect is that they fail to conform to this rationalistic ideal. Hence those sentences which sound so strangely in the mouth of Locke, the sensationalist.

“It is the contemplation of our abstract ideas that alone is able to afford us general knowledge.”[1765] “The true method of advancing knowledge is by considering our abstract ideas.”[1766] ”[Did we know the real essence of gold] it would be no more necessary that gold should exist, and that we should make experiments upon it, than it is necessary for the knowing of the properties of a triangle, that a triangle should exist in any matter: the idea in our minds would serve for the one as well as for the other.”[1767] “In the knowledge of bodies, we must be content to glean what we can from particular experiments, since we cannot, from a discovery of their real essences, grasp at a time whole sheaves, and in bundles comprehend the nature and the properties of whole species together.”

Locke’s empirical doctrine of knowledge is thus based upon a rationalistic theory of the real. It is not, he holds, the constitution of reality, but the de facto limitations of our human faculties which make empirical induction the only practicable mode of discovery in natural science. Indeed, Locke gives more extreme expression than even Descartes does, to the mystically conceived mathematical method. Being ignorant of mathematics, and not over well-informed even in the physical sciences, Locke was not checked by any too close acquaintance with the real character and necessary limits of this method; and he accordingly makes statements in that unqualified fashion which seldom fails to betray the writer who is expounding views which he has not developed for himself by first-hand study of the relevant facts.