I The Unresolved Problem of the Grundlegung
The announced aim of Kant's moral philosophy, as stated most clearly and unambiguously in the Foundations of the Metaphysics of Morals, is to discover unconditionally valid principles of practical reason. Kant conceives his task as falling into three parts, exactly corresponding to the three Sections of the Foundations. First, he must identify and state the Moral Law, the highest principle of practical reason, by which all rational agents, merely in virtue of being rational agents, are bound. Secondly, he must demonstrate that the Highest Moral Principle can be derived, entirely a priori, from a conceptual analysis of Practical Reason. Finally, in light of the teaching of the First Critique, Kant must connect up his conclusions concerning the principles guiding the choices of rational agents with our experience of ourselves as causally determined beings in the realm of appearance.
In sum, then, the Foundations attempts to identify and state the principle governing the actions of rational agents; to derive that principle from an a priori analysis of rational agency, thereby proving that all rational agents, simply in virtue of their rational agency, necessarily act out of respect for that principle; and to demonstrate that we, as conditioned beings in the realm of appearance, must act as though we know ourselves to be rational agents, even though such knowledge is, strictly speaking, unavailable to us.
It is, of course, a matter of considerable controversy whether Kant succeeds in achieving all three, or indeed any, of these goals. The first is the least controversial, for it merely involves showing that Kant and his audience of North Prussian Pietists share a belief in a particularly rigoristic formalism. The achievement of the third goal, involving as it does the entire complex metaphysical and epistemological theoretical structure of the First Critique, is best left to one side in an discussion such as this. But the second of Karat's undertakings warrants our closest attention, for it is here that we find the greatest controversy arising among students of Kant's moral philosophy.
The controversy surrounding Kant's derivation of the Categorical Imperative concerns not the validity of the derivation but its significance. Many students of Kant's philosophy, and more broadly many students of moral and political philosophy, will readily grant that some principle of formal consistency of willing can be derived a priori from an analysis of agency and rationality as such. What makes Kant's moral theory so controversial, especially in regard to his second undertaking, is the extraordinary claim that the purely a priori formal principle of consistency in willing is sufficient to identify, from among the host of possible moral rules, just those which reason commands, and which therefore constitute the substance of morality.
Kant actually tries three times in the Foundations to establish the universal validity of unconditional; moral principles. The first attempt is the famous four examples of the categorical Imperative. Kant's arguments against suicide and self-indulgent laziness are hopelessly inadequate. Both make explicit and utterly unjustified appeal to the supposed objective natural purpose of some human capacity or psychological tendency. The argument concerning ungenerosity is rather interesting, but it is ultimately inadequate. For a variety of reasons, most scholarly and philosophical attention has focused on the second argument, concerning false promising.
The standard reconstruction of the false promising example, with which I entirely agree, is to construe promising as a social practice defined by a system of implicit, but clearly understood, rules, among which rather prominently featured is a rule against false promising. On this view, when I utter the words "I promise" in the appropriate social context, I am implicitly endorsing, or committing myself to, or willing, in Kant's language, the entire system of rules that constitute the practice of promising. But it takes only a little reflection to recognize that the injunction against false promising is not actually a categorical substantive moral command. Rather, it is hypothetical in form. What Kant's argument, suitably reconstructed, demonstrates is that false promising is incompatible with the practice of promise-making, from which it follows that we must, in all consistency, choose either not to endorse, participate in, and commit ourselves to the practice of promising or else not to make false promises. But there is nothing in Kant's argument to dissuade us from forswearing the institution of promising altogether. The crucial point is that Kant has no plausible a priori argument in support of the claim that a rational agent will necessarily enter into the practice of promising, or more generally into whatever overarching practice is implicit in the truthful use of language, from which the obligation in particular to participate in the practice of promise-making might be derived. In effect, Kant is at this point in his exposition unwittingly assuming that the agents of whom he is speaking have some minimal commitment to honorable social interaction with which, as he quite rightly argues, false promising is logically incompatible. To the thorough reprobate who simply rejects such a commitment, however, Kant has no valid objection.
Thus, Kant's first two attempts to extract substantive moral principles from his purely formal analysis of rational willing fail because of two fundamental problems: First, his failure to demonstrate that rational agents have a standing, unconditional obligation to enter into, or participate in, rule-governed social practices in the context of which the notion of contradictory willing can be fleshed out and given substance; and Second, his failure to identify obligatory ends, adoption of which follows necessarily from the mere fact of being a rational agent, and the existence of which would, in a different but equivalent way, provide substantial content for the purely formal principle of consistency in willing. Kant's third attempt in the Foundations is directed precisely at compensating for both of these failures - namely, his invocation of the social contract tradition of political theory under the guise of what he calls a "Realm of Ends."
By "realm" I understand the systematic union of different rational beings through common laws. Because laws determine ends with regard to their universal validity, if we abstract from the personal difference of rational beings and thus from all content of their private ends, we can think of a whole of all ends in systematic connection, a whole of rational beings as ends in themselves as well as of the particular ends that each may set for himself. This is a realm of ends, which is possible on the aforesaid principles. For all rational beings stand under the law that each of them should treat himself and all others never merely as means but in every case also as an end in himself. Thus there arises a systematic union of rational beings through common objective laws. This is a realm that may be called a realm of ends (certainly only an ideal), because what these laws have in view is just the relation of these beings to each other as ends and means.
A rational being belongs to the realm of ends as a member when he gives universal laws in it while also himself subject to these laws. He belongs to it as sovereign when he, as legislating, is subject to the will of no other. The rational being must regard himself always as legislative in a realm of ends possible through the freedom of the will, whether he belongs to it as member or as sovereign. He cannot maintain the latter position merely through the maxims of his will but only when he is a completely independent being without need and with power adequate to his will.
Morality, therefore, consists in the relation of every action to that legislation through which alone a realm of ends is possible. It must be able to arise from his will, whose principle then is to take no action according to any maxim which would be inconsistent with its being a universal law and thus to act only so that the will through its maxims could regard itself at the same time as universally lawgiving
This language is, of course, a direct echo of Rousseau's characterization of the republic brought into existence by the social contract. It specifies the procedure by which a collection of self-interested individuals can transform themselves into a republic by entering into the mutual agreement referred to as a social contract.
At the close of the Foundations, despite Kant's introduction of the evocative notion of humanity as an end in itself, and his invocation of a Rousseauean conception of a republic regulated by a social contract, we are left with the two problems outlined earlier: First, how to demonstrate that rational agents as such must, in all consistency, enter into collective agreements that establish structures of social practices in the context of which substantial meaning can be given to the notion of contradictory willing; and Second, how to demonstrate that rational agents who have thus constituted themselves a realm of ends or republic will, qua rational, arrive at a single universal, necessary, and therefore objective set of substantive laws as the content of their collective rational willing .