For although a will which is subject to laws may be attached to this law by means of an interest, yet a will which is itself a supreme lawgiver so far as it is such cannot possibly depend on any interest, since a will so dependent would itself still need another law restricting the interest of its self-love by the condition that it should be valid as universal law.

Thus the principle that every human will is a will which in all its maxims gives universal laws [Footnote:  I may be excused from adducing examples to elucidate this principle, as those which have already been used to elucidate the categorical imperative and its formula would all serve for the like purpose here.] provided it be otherwise justified, would be very well adapted to be the categorical imperative, in this respect, namely, that just because of the idea of universal legislation it is not based on any interest, and therefore it alone among all possible imperatives can be unconditional.  Or still better, converting the proposition, if there is a categorical imperative (i.e. a law for the will of every rational being), it can only command that everything be done from maxims of one’s will regarded as a will which could at the same time will that it should itself give universal laws, for in that case only the practical principle and the imperative which it obeys are unconditional, since they cannot be based on any interest.

Looking back now on all previous attempts to discover the principle of morality, we need not wonder why they all fail.  It was seen that man was bound to laws by duty, but it was not observed that the laws to which he is subject are only those of his own giving, though at the same time they are universal, and that he is only bound to act in conformity with his own will; a will, however, which is designed by nature to give universal laws.  For when one has conceived man only as subject to a law (no matter what), then this law required some interest, either by way of attraction or constraint, since it did not originate as a law from his own will, but this will was according to a law obliged by something else to act in a certain manner.  Now by this necessary consequence all the labour spent in finding a supreme principle of duty was irrevocably lost.  For men never elicited duty, but only a necessity of acting from a certain interest.  Whether this interest was private or otherwise, in any case the imperative must be conditional, and could not by any means be capable of being a moral command.  I will therefore call this the principle of Autonomy of the will, in contrast with every other which I accordingly reckon as Heteronomy? [Footnote:  Cp.  “Critical Examination of Practical Reason,” p. 184.]

The conception of every rational being as one which must consider itself as giving in all the maxims of its will universal laws, so as to judge itself and its actions from this point of view—­this conception leads to another which depends on it and is very fruitful, namely, that of a kingdom of ends.