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
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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 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 do so-and-so if you wish to achieve such-andsuch 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
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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
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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
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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
