Kant had learned this much from Hume, that causation is essentially a relation of antecedence and consequence in time; and apparently his way of "categorising" the relation—i.e., of proving its apriority—is to represent it as the logical form of reason and consequent masquerading, so to speak, under the intuitional time-form. Yet he frequently speaks of our senses as being affected by things in themselves, implying that the resulting sensations are somehow caused by those otherwise unknown entities. But since things in themselves do not, according to Kant, exist in space and time, they cannot be causally related to phenomena or to anything else.
In his criticism of Pure Reason, properly so called—that is, of inferences made by human faculty with
regard to questions transcending all experience—Kant shows that of such things nothing can be known. The ideality of time and space once taken as proved, this amount of agnosticism seems to follow as a matter of course. It is idle to speculate about the possible extent or duration of a universe that cannot be described in terms of coexistence and succession. For each of us at the dissolution of our bodily organism time itself, and therefore existence as alone we conceive it, comes to an end. The law of causation, applying as it does to phenomena alone, offers no evidence for the existence of a God who transcends phenomena. Kant, however, is not satisfied with such a simple and summary procedure as this. He tries to show, with most unnecessary pedantry, that the conditional synthesis of the Understanding inevitably leads thought on to the unconditional synthesis of the Reason only to find itself lost in a hopeless welter of paralogisms and self-contradictions.
At this stage we are handed over to the guidance of what Kant calls the Practical Reason. This faculty gives a synthesis for conduct, as Pure Reason gave a synthesis for intelligence. All reason demands uniformity, order, law; only what in theory is recognised as true has in practice to be imposed as right. In this way Kant arrives at his formula of absolute morality: Act so that the principle of thy conduct may be the law for all rational beings. He calls this the Categorical Imperative, as distinguished from such hypothetical imperatives as: Act this way if you wish to be happy either here or hereafter; or, act as public opinion tells you. Moreover, the motive, as distinguished from the end of moral action, should not be calculating self-interest nor uncalculating impulse, but simply desire to fulfil the law as such. Previous moralists had set up
the greatest happiness of the greatest number as the end of action, and such an aim does not lie far from Kant's philosophy; but they could think of no better motive for pursuing it than self-love or a rather undefined social instinct; and their summum bonum would take the happiness of irrational animals into account, while Kant absolutely subordinates the interests of these to human good. A further coincidence between the Utilitarian and the Kantian ethics is that in the latter also the happiness of others, not their perfection, should be the end and aim of each. Finally, the philosophy of Pure Reason adopts from contemporary French thought as the governing idea of political organisation what was long to be a principle of English Utilitarianism—"the liberty of each, bounded only by the equal liberty of all."
Nevertheless, the old postulate of a necessary connection between virtue and individual happiness reappears in Kant's ethical theory, and leads to the construction of a new religious philosophy. His critique had left no place for the old theology, nor yet for that doctrine of free-will so dear to most theologians. Its whole object had been to vindicate against Hume the necessity and universality of causation. Human actions then must, like all other phenomena, form an unbroken chain of antecedents and consequents. Nor does Kant conceal his conviction that, with sufficient knowledge and powers of calculation, a man's whole future conduct might be foretold. Nevertheless, under the eighteenth-century idea of man as naturally the creature of passion or self-interest, he claims for us, as moral agents, the power of choosing to obey duty in preference to either. And this freedom is supposed to be made conceivable by the subjectivity of time and causation, outside of which,
as a thing in itself, stands the moral will. That morality, whether as action or mere intention, involves succession in time is utterly ignored. Nor is this all. Assuming without warrant that the moral law demands an ultimate coincidence between happiness and virtue, made impossible in this life by human weakness, Kant argues that there must be an unending future life to secure time enough for working out a problem whose solution is infinitely remote. And, finally, there must be an omnipotent moral God to provide facilities for undertaking that somewhat gratuitous Psyche's task. Before Kant moral theology had argued that the Judge of all the world must do right, apportioning happiness to desert. It was reserved for him to argue, conversely, that for right to be done such a Judge must exist, and that therefore he does exist.
In appreciating the services of Kant to philosophy we must guard ourselves against being influenced by the extravagant panegyrics of his countrymen, whose passion for square circles he so generously gratifies. Still, after every deduction for mere Laputian pedantry has been made, the balance of fruitful suggestion remains vast. (i.) The antithesis of object and subject, although not counted among the categories of his Critique, has remained a prime category of thought ever since. (ii.) The idea of a necessary limit to human knowledge, given by the very theory of that knowledge, as distinguished from the Scepticism of the Greeks—in other words, what we now call Agnosticism—may not be final, but it still remains to be dealt with. (iii.) The possibility of reducing à priori knowledge to a form of unconscious experience has put an end to dogmatic metaphysics. (iv.) The problems of Time and Space have taken a central place in speculation; it has been
shown—what Hume did not see—that Causation has the certainty of a mathematical axiom; and it has been made highly probable that all these difficulties may find their solution in a larger interpretation of experience. (v.) Morality has been definitely dissociated from the appeal to selfish interests, whether in this life or in another.
We have now to trace, within the limits prescribed by the nature of this work, the development of philosophy under Kant's German successors.