Notwithstanding this force and ease of application, a categorical Imperative has not yet been proved a priori actually existent; and it was allowed that it could not be proved empirically, elements of inclination, interest, &c., being inconsistent with morality.  The real question is this:  Is it a necessary law that all rational beings should act on maxims that they can wish, to become universal laws?  If so, this must be bound up with the very notion of the will of a rational being; the relation of the will to itself being to be determined a priori by pure Reason.  The Will is considered as a power of self-determination to act according to certain laws as represented to the mind, existing only in rational beings.  And, if the objective ground of self-determination, or End, is supplied by mere Reason, it must be the same for all rational beings. Ends may be divided into Subjective, resting upon individual Impulses or subjective grounds of desire; and Objective, depending on Motives or objective grounds of Volition valid for all rational beings.  The principles of action are, in the one case, Material, and, in the other, Formal, i.e., abstracted from all subjective ends.  Material ends, as relative, beget only hypothetical Imperatives.  But, supposed some thing, the presence of which in itself has an absolute value, and which, as End-in-self, can be a ground of fixed laws; there, and there only, can be the ground of a possible categorical Imperative, or Law of Practice.

Now, such an End-in-self (not a thing with merely conditional value,—­a means to be used arbitrarily) is Man and every rational being, as Person.  There is no other objective end with absolute value that can supply to the Reason the supreme practical principle requisite for turning subjective principles of action into objective principles of volition.  Rational Nature as End-in-self is a subjective principle to a man having this conception of his own being, but becomes objective when every rational being has the same from the same ground in Reason.  Hence a new form (the second) to the practical Imperative:  Act so as to use Humanity (Human Nature) as well in your own person, as in the person of another, ever as end also, and never merely as means.

To this new formula, the old examples are easily squared.  Suicide is using one’s person as a mere means to a tolerable existence; breaking faith to others is using them as means, not as ends-in-self; neglect of self-cultivation is the not furthering human nature as end-in-self in one’s own person; withholding help is refusing to further Humanity as end-in-self through the medium of the aims of others. [In a note he denies that ‘the trivial, Do to others as you would,’ &c., is a full expression of the law of duty:  it contains the ground, neither of duties to self; nor of duties of benevolence to others, for many would forego receiving good on conditions of not conferring it; nor of the duty of retribution, for the malefactor could turn it against his judge, &c.]