Kant’s assertion of the “Autonomy of the Practical Reason” thus has the very opposite effect to that which he desired; it makes his Ethics ultimately and hopelessly “heteronomous.” His Moral Law is “independent” of Metaphysics only in the sense that according to him we can know it independently; he holds that we can only infer that there is Freedom, from the fact that the Moral Law is true. And so far as he keeps strictly to this view, he does avoid the error, into which most metaphysical writers fall, of allowing his opinions as to what is real to influence his judgments of what is good. But he fails to see that on his view the Moral Law is dependent upon Freedom in a far more important sense than that in which Freedom depends on the Moral Law. He admits that Freedom is the ratio essendi of the Moral Law, whereas the latter is only ratio cognoscendi of Freedom. And this means that, unless Reality be such as he says, no assertion that “This is good” can possibly be true: it can indeed have no meaning. He has, therefore, furnished his opponents with a conclusive method of attacking the validity of the Moral Law. If they can only show by some other means (which he denies to be possible but leaves theoretically open) that the nature of Reality is not such as he says, he cannot deny that they will have proved his ethical principle to be false. If that “This ought to be done” means “This is willed by a Free Will,” then, if it can be shown that there is no Free Will which wills anything, it will follow that nothing ought to be done.
76. And Kant also commits the fallacy of supposing that “This ought to be” means “This is commanded.” He conceives the Moral Law to be an Imperative. And this is a very common mistake. “This ought to be,” it is assumed, must mean “This is commanded”; nothing, therefore, would be good unless it were commanded; and since commands in this world are liable to be erroneous, what ought to be in its ultimate sense means “what is commanded by some real supersensible authority.” With regard to this authority it is, then, no longer possible to ask “Is it righteous?” Its commands cannot fail to be right, because to be right means to be what it commands. Here, therefore, law, in the moral sense, is supposed analogous to law, in the legal sense, rather than, as in the last instance, to law in the natural sense. It is supposed that moral obligation is analogous to legal obligation, with this difference only that whereas the source of legal obligation is earthly, that of moral obligation is heavenly. Yet it is obvious that if by a source of obligation is meant only a power which binds you or compels you to do a thing, it is not because it does do this that you ought to obey it. It is only if it be itself so good, that it commands and enforces only what is good, that it can be a source of moral obligation. And in that case what it commands and enforces would be good, whether commanded and enforced or not. Just that which makes an obligation legal, namely the fact that it is commanded by a certain kind of authority, is entirely irrelevant to a moral obligation. However an authority be defined, its commands will be morally binding only if they are—morally binding; only if they tell us what ought to be or what is a means to that which ought to be.
77. In this last error, in the supposition that when I say “You ought to do this” I must mean “You are commanded to do this,” we have one of the reasons which has led to the supposition that the particular supersensible property by reference to which good must be defined is Will. And that ethical conclusions may be obtained by enquiring into the nature of a fundamentally real Will seems to be by far the commonest assumption of Metaphysical Ethics at the present day. But this assumption seems to owe its plausibility, not so much to the supposition that “ought” expresses a “command,” as to a far more fundamental error. This error consists in supposing that to ascribe certain predicates to a thing is the same thing as to say that that thing is the object of a certain kind of psychical state. It is supposed that to say that a thing is real or true is the same thing as to say that it is known in a certain way; and that the difference between the assertion that it is good and the assertion that it is real—between an ethical, therefore, and a metaphysical proposition—consists in the fact that whereas the latter asserts its relation to Cognition the former asserts its relation to Will.
Now that this is an error has been already shown in Chapter I. That the assertion “This is good” is not identical with the assertion “This is willed,” either by a supersensible will, or otherwise, nor with any other proposition, has been proved; nor can I add anything to that proof. But in face of this proof it may be anticipated that two lines of defence may be taken up. (1) It may be maintained that, nevertheless,
