Hume had proved that the law of causality is not analytic, and had inferred that we could not be certain of its truth. Kant accepted the view that it is synthetic, but nevertheless maintained that it is known a priori. He maintained that arithmetic and geometry are synthetic, but are likewise a priori. He was thus led to formulate his problem in these terms:
How are synthetic judgements a priori possible?
The answer to this question, with its consequences, constitutes the main theme of The Critique of Pure Reason.
Kant’s solution of the problem was one in which he felt great confidence. He had spent twelve years in looking for it, but took only a few months to write his whole long book after his theory had taken shape. In the preface to the first edition he says: “I venture to assert that there is not a single metaphysical problem which has not been solved, or for the solution of which the key at least has not been supplied.” In the preface to the second edition he compares himself to Copernicus, and says that he has effected a Copernican revolution in philosophy.
According to Kant, the outer world causes only the matter of sensation, but our own mental apparatus orders this matter in space and time, and supplies the concepts by means of which we understand experience. Things in themselves, which are the causes of our sensations, are unknowable; they are not in space or time, they are not substances, nor can they be described by any of those other general concepts which Kant calls “categories.” Space and time are subjective, they are part of our apparatus of perception. But just because of this, we can be sure that whatever we experience will exhibit the characteristics dealt with by geometry and the science of time. If you always wore blue spectacles, you could be sure of seeing everything blue (this is not Kant’s illustration). Similarly, since you always wear spatial spectacles in your mind, you are sure of always seeing everything in space. Thus geometry is a priori in the sense that it must be true of everything experienced, but we have no reason to suppose that anything analogous is true of things in themselves, which we do not experience.
Space and time, Kant says, are not concepts; they are forms of “intuition.” (The German word is “Anschauung,” which means literally “looking at” or “view.” The word “intuition,” though the accepted translation is not altogether a satisfactory one.) There are also, however, a priori concepts; these are the twelve “categories,” which Kant derives from the forms of the syllogism. The twelve categories are divided into four sets of three: (1) of quantity: unity, plurality, totality; (2) of quality: reality, negation, limitation; (3) of relation: substance-and-accident, cause-and-effect, reciprocity; (4) of modality: possibility, existence, necessity. These are subjective in the same sense in which space and time are—that is to say, our mental constitution is such that they are applicable to whatever we experience, but there is no reason to suppose them applicable to things in themselves. As regards cause, however, there is an inconsistency, for things in themselves are regarded by Kant as causes of sensations, and free volitions are held by him to be causes of occurrences in space and time. This inconsistency is not an accidental oversight; it is an essential part of his system.
A large part of The Critique of Pure Reason is occupied in showing the fallacies that arise from applying space and time or the categories to things that are not experienced. When this is done, so Kant maintains, we find ourselves troubled by “antinomies”—that is to say, by mutually contradictory propositions each of which can apparently be proved. Kant gives four such antinomies, each consisting of thesis and antithesis.
In the first, the thesis says: “The world has a beginning in time, and is also limited as regards space.” The antithesis says: “The world has no beginning in time, and no limits in space; it is infinite as regards both time and space.”
The second antinomy proves that every composite substance both is, and is not, made up of simple parts.
The thesis of the third antinomy maintains that there are two kinds of causality, one according to the laws of nature, the other that of freedom; the antithesis maintains that there is only causality according to the laws of nature.
The fourth antinomy proves that there is, and is not, an absolutely necessary Being.
This part of the Critique greatly influenced Hegel, whose dialectic proceeds wholly by way of antinomies.
In a famous section, Kant sets to work to demolish all the purely intellectual proofs of the existence of God. He makes it clear that he has other reasons for believing in God; these he was to set forth later in The Critique of Practical Reason. But for the time being his purpose is purely negative.
There are, he says, only three proofs of God’s existence by pure reason; these are the ontological proof, the cosmological proof, and the physico-theological proof.
The ontological proof, as he sets it forth, defines God as the ens realissimum, the most real being; i.e., the subject of all predicates that belong to being absolutely. It is contended, by those who believe the proof valid, that, since “existence” is such a predicate, this subject must have the predicate “existence,” i.e., must exist. Kant objects that existence is not a predicate. A hundred thalers that I merely imagine may, he says, have all the same predicates as a hundred real thalers.
The cosmological proof says: If anything exists, then an absolutely necessary Being must exist; now I know that I exist; therefore an absolutely necessary Being exists, and this must be the ens realissimum. Kant maintains that the last step in this argument is the ontological argument over again, and that it is therefore refuted by what has been already said.
The physico-theological proof is the familiar argument from design, but in a metaphysical dress. It maintains that the universe exhibits an order which is evidence of purpose. This argument is treated by Kant with respect, but he points out that, at best, it proves only an Architect, not a Creator, and therefore cannot give an adequate conception of God. He concludes that “the only theology of reason which is possible is that which is based upon moral laws or seeks guidance from them.”
God, freedom, and immortality, he says, are the three “ideas of reason.” But although pure reason leads us to form these ideas, it cannot itself prove their reality. The importance of these ideas is practical, i.e., connected with morals. The purely intellectual use of reason leads to fallacies; its only right use is directed to moral ends.
The practical use of reason is developed briefly near the end of The Critique of Pure Reason, and more fully in The Critique of Practical Reason ( 1786). The argument is that the moral law demands justice, i.e., happiness proportional to virtue. Only Providence can insure this, and has evidently not insured it in this life. Therefore there is a God and a future life; and there must be freedom, since otherwise there would be no such thing as virtue.
Kant’s ethical system, as set forth in his Metaphysic of Morals (1785), has considerable historical importance. This book contains the “categorical imperative,” which, at least as a phrase, is familiar outside the circle of professional philosophers. As might be expected, Kant will have nothing to do with utilitarianism, or with any doctrine which gives to morality a purpose outside itself. He wants, he says, “a completely isolated metaphysic of morals, which is not mixed with any theology or physics or hyperphysics.” All moral concepts, he continues, have their seat and origin wholly a priori in the reason. Moral worth exists only when a man acts from a sense of duty; it is not enough that the act should be such as duty might have prescribed. The tradesman who is honest from self-interest, or the man who is kind from benevolent impulse, is not virtuous. The essence of morality is to be derived from the concept of law; for, though everything in nature acts according to laws, only a rational being has the power of acting according to the idea of a law, i.e., by Will. The idea of an objective principle, in so far as it is compelling to the will, is called a command of the reason, and the formula of the command is called an imperative.
There are two sorts of imperative: the hypothetical imperative, which says “You must d
o so-and-so if you wish to achieve such-and-such an end”; and the categorical imperative, which says that a certain kind of action is objectively necessary, without regard to any end. The categorical imperative is synthetic and a priori. Its character is deduced by Kant from the concept of Law:
“If I think of a categorical imperative, I know at once what it contains. For as the imperative contains, besides the Law, only the necessity of the maxim to be in accordance with this law, but the Law contains no condition by which it is limited, nothing remains over but the generality of a law in general, to which the maxim of the actions is to be conformable, and which conforming alone presents the imperative as necessary. Therefore the categorical imperative is a single one, and in fact this: “Act only according to a maxim by which you can at the same time will that it shall become a general law.” Or: “Act as if the maxim of your action were to become through your will a general natural law.”
Kant gives as an illustration of the working of the categorical imperative that it is wrong to borrow money, because if we all tried to do so there would be no money left to borrow. One can in like manner show that theft and murder are condemned by the categorical imperative. But there are some acts which Kant would certainly think wrong but which cannot be shown to be wrong by his principles, for instance suicide; it would be quite possible for a melancholic to wish that everybody should commit suicide. His maxim seems, in fact, to give a necessary but not a sufficient criterion of virtue. To get a sufficient criterion, we should have to abandon Kant’s purely formal point of view, and take some account of the effects of actions. Kant, however, states emphatically that virtue does not depend upon the intended result of an action, but only on the principle of which it is itself a result; and if this is conceded, nothing more concrete than his maxim is possible.
Kant maintains, although his principle does not seem to entail this consequence, that we ought so to act as to treat every man as an end in himself. This may be regarded as an abstract form of the doctrine of the rights of man, and it is open to the same objections. If taken seriously, it would make it impossible to reach a decision whenever two people’s interests conflict. The difficulties are particularly obvious in political philosophy, which requires some principle, such as preference for the majority, by which the interests of some can, when necessary, be sacrificed to those of others. If there is to be any ethic of government, the end of government must be one, and the only single end compatible with justice is the good of the community. It is possible, however, to interpret Kant’s principle as meaning, not that each man is an absolute end, but that all men should count equally in determining actions by which many are affected. So interpreted, the principle may be regarded as giving an ethical basis for democracy. In this interpretation, it is not open to the above objection.
Kant’s vigour and freshness of mind in old age are shown by his treatise on Perpetual Peace ( 1795 ). In this work he advocates a federation of free States, bound together by a covenant forbidding war. Reason, he says, utterly condemns war, which only an international government can prevent. The civil constitution of the component States should, he says, be “republican,” but he defines this word as meaning that the executive and the legislative are separated. He does not mean that there should be no king; in fact, he says that it is easiest to get a perfect government under a monarchy. Writing under the impact of the Reign of Terror, he is suspicious of democracy; he says that it is of necessity despotism, since it establishes an executive power. “The ‘whole people,’ so-called, who carry their measures are really not all, but only a majority: so that here the universal will is in contradiction with itself and with the principle of freedom.” The phrasing shows the influence of Rousseau, but the important idea of a world federation as the way to secure peace is not derived from Rousseau.
Since 1933, this treatise has caused Kant to fall into disfavour in his own country.
C. KANT’S THEORY OF SPACE AND TIME
The most important part of The Critique of Pure Reason is the doctrine of space and time. In this section I propose to make a critical examination of this doctrine.
To explain Kant’s theory of space and time clearly is not easy, because the theory itself is not clear. It is set forth both in The Critique of Pure Reason and in the Prolegomena; the latter exposition is the easier, but is less full than that in the Critique. I will try first to expound the theory, making it as plausible as I can; only after exposition will I attempt criticism.
Kant holds that the immediate objects of perception are due partly to external things and partly to our own perceptive apparatus. Locke had accustomed the world to the idea that the secondary qualities—colours, sounds, smells, etc.—are subjective, and do not belong to the object as it is in itself. Kant, like Berkeley and Hume, though in not quite the same way, goes further, and makes the primary qualities also subjective. Kant does not at most times question that our sensations have causes, which he calls “things-in-themselves” or “noumena.” What appears to us in perception, which he calls a “phenomenon,” consists of two parts: that due to the object, which he calls the “sensation,” and that due to our subjective apparatus, which, he says, causes the manifold to be ordered in certain relations. This latter part he calls the form of the phenomenon. This part is not itself sensation, and therefore not dependent upon the accident of environment; it is always the same, since we carry it about with us, and it is a priori in the sense that it is not dependent upon experience. A pure form of sensibility is called a “pure intuition” (Anschauung); there are two such forms, namely space and time, one for the outer sense, one for the inner.
To prove that space and time are a priori forms, Kant has two classes of arguments, one metaphysical, the other epistemological, or, as he calls it, transcendental. The former class of arguments are taken directly from the nature of space and time, the latter indirectly from the possibility of pure mathematics. The arguments about space are given more fully than those about time, because it is thought that the latter are essentially the same as the former.
As regards space, the metaphysical arguments are four in number.
(1) Space is not an empirical concept, abstracted from outer experiences, for space is presupposed in referring sensations to something external, and external experience is only possible through the presentation of space.
(2) Space is a necessary presentation a priori, which underlies all external perceptions; for we cannot imagine that there should be no space, although we can imagine that there should be nothing in space.
(3) Space is not a discursive or general concept of the relations of things in general, for there is only one space, of which what we call “spaces” are parts, not instances.
(4) Space is presented as an infinite given magnitude, which holds within itself all the parts of space; this relation is different from that of a concept to its instances, and therefore space is not a concept but an Anschauung.
The transcendental argument concerning space is derived from geometry. Kant holds that Euclidean geometry is known a priori, although it is synthetic, i.e., not deducible from logic alone. Geometrical proofs, he considers, depend upon the figures; we can see, for instance, that, given two intersecting straight lines at right angles to each other, only one straight line at right angles to both can be drawn through their point of intersection. This knowledge, he thinks, is not derived from experience. But the only way in which my intuition can anticipate what will be found in the object is if it contains only the form of my sensibility, antedating in my subjectivity all the actual impressions. The objects of sense must obey geometry, because geometry is concerned with our ways of perceiving, and therefore we cannot perceive otherwise. This explains why geometry, though synthetic, is a priori and apodeictic.
The arguments with regard to time are essentially the same, except that arithmetic replaces geometry with the contention that counting takes time.
Let us now examine these arguments one by one.
The firs
t of the metaphysical arguments concerning space says: “Space is not an empirical concept abstracted from external experiences. For in order that certain sensations may be referred to something outside me [i.e., to something in a different position in space from that in which I find myself], and further in order that I may be able to perceive them as outside and beside each other, and thus as not merely different, but in different places, the presentation of space must already give the foundation [zum Grunde liegen].” Therefore external experience is only possible through the presentation of space.
The phrase “outside me [i.e., in a different place from that in which I find myself]” is a difficult one. As a thing-in-itself, I am not anywhere, and nothing is spatially outside me; it is only my body as a phenomenon that can be meant. Thus all that is really involved is what comes in the second part of the sentence, namely that I perceive different objects as in different places. The image which arises in one’s mind is that of a cloak-room attendant who hangs different coats on different pegs; the pegs must already exist, but the attendant’s subjectivity arranges the coats.
There is here, as throughout Kant’s theory of the subjectivity of space and time, a difficulty which he seems to have never felt. What induces me to arrange objects of perception as I do rather than otherwise? Why, for instance, do I always see people’s eyes above their mouths and not below them? According to Kant, the eyes and the mouth exist as things in themselves, and cause my separate percepts, but nothing in them corresponds to the spatial arrangement that exists in my perception. Contrast with this the physical theory of colours. We do not suppose that in matter there are colours in the sense in which our percepts have colours, but we do think that different colours correspond to different wave-lengths. Since waves, however, involve space and time, there cannot, for Kant, be waves in the causes of our percepts. If, on the other hand, the space and time of our percepts have counterparts in the world of matter, as physics assumes, then geometry is applicable to these counterparts, and Kant’s arguments fail. Kant holds that the mind orders the raw material of sensation, but never thinks it necessary to say why it orders it as it does and not otherwise.
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