change it into the knowledge of a being so acting, not even into the knowledge of the possibility of such a being. This vacant place is now filled by pure practical reason with a definite law of causality in an intelligible world (causality with freedom), namely, the moral law. Speculative reason does not hereby gain anything as regards its insight, but only as regards the certainty of its problematical notion of freedom, which here obtains objective reality, which, though only practical, is nevertheless undoubted. Even the notion of causality- the application, and consequently the signification, of which holds properly only in relation to phenomena, so as to connect them into experiences (as is shown by the Critique of Pure Reason)- is not so enlarged as to extend its use beyond these limits. For if reason sought to do this, it would have to show how the logical relation of principle and consequence can be used synthetically in a different sort of intuition from the sensible; that is how a causa noumenon is possible. This it can never do; and, as practical reason, it does not even concern itself with it, since it only places the determining principle of causality of man as a sensible creature (which is given) in pure reason (which is therefore called practical); and therefore it employs the notion of cause, not in order to know objects, but to determine causality in relation to objects in general. It can abstract altogether from the application of this notion to objects with a view to theoretical knowledge (since this concept is always found a priori in the understanding even independently of any intuition). Reason, then, employs it only for a practical purpose, and hence we can transfer the determining principle of the will into the intelligible order of things, admitting, at the same time, that we cannot understand how the notion of cause can determine the knowledge of these things. But reason must cognise causality with respect to the actions of the will in the sensible world in a definite manner; otherwise, practical reason could not really produce any action. But as to the notion which it forms of its own causality as noumenon, it need not determine it theoretically with a view to the cognition of its supersensible existence, so as to give it significance in this way. For it acquires significance apart from this, though only for practical use, namely, through the moral law. Theoretically viewed, it remains always a pure a priori concept of the understanding, which can be applied to objects whether they have been given sensibly or not, although in the latter case it has no definite theoretical significance or application, but is only a formal, though essential, conception of the understanding relating to an object in general. The significance which reason gives it through the moral law is merely practical, inasmuch as the idea of the law of causality (of the will) has self causality, or is its determining principle.