History of Western Philosophy - Bertrand Russell [404]
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 physicotheological 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 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-and-such an end'; and the categorical imperative, which says that a certain kind of action is objectively necessary,