The Categorical Imperative and Deduction

Kant makes clear that no deduction of the moral law is either possible nor necessary. He makes this claim on account of a distinction between our theoretical and practical faculties of reason. However, Kant has explained that there is another process for arriving at a conclusion regarding the objective reality of the moral law by use of a "warrant" or "credential" that allows us to make this move. This has further implications for Kant's argument, as he will use it as an attempt to break the notorious circle of the Groundwork of the Metaphysics of Morals. Why such deduction cannot (nor needs to) needs to be explained further before we may move towards the other points of his argument in proving the objective reality of the moral law.

By deduction Kant refers to the process of a justification of the objective and universal validity of the moral law and the producing the possibility of how such a synthetic a priori proposition could be possible (177). This, he believes, can only be done through the use of pure theoretical reason for they include objects of possible experience - for which categories of the understanding can legitimately cognize. The distinction is made yet again, between pure theoretical and practical reason, in that the former only experience can account for any sort of justification of an object's validity. This, however, is not the case in our practical reason - and hence, a deduction on the grounds of empirical proofs is not possible. What is deduced in our theoretical reason is dependent upon other factors. This reasoning must draw its evidence about its possible reality from experience alone, which in turn is dependent upon grounds on the possibility of principles of experience (177). This type of deduction simply isn't necessary either. Kant states that the moral law is disinterested in cognizing the possibility of objects that could be given through anything outside of reason, since the moral law is the determining grounds for our wills through the use of our pure practical reason (177). Instead, Kant argues that there is another means for which we can possibly arrive at an objective validity to the existence of the moral law. Kant further holds that the moral law provides all the justification for its established reality in its own constitution. Therefore, the deduction through theoretical reason is not necessary for validating the existence of the moral law.

Kant returns to the relationship between freedom, causality, and the moral law to substitute the problem encountered in attempting to deduce the moral law in theoretical reason.. He constructs then a relationship between causality and the moral law, "the moral law, is in fact, a law of causality through freedom and hence a law of the possibility of a supersensible nature" (178). Thus, the moral law can be used as a principle in our practical deduction of the moral law. Whereas we had to assume the possibility of freedom, we can now (through the relationship between the moral law and freedom) move towards extracting its objective reality. The law of causality (as applied to the sensible world) held that each and every sensible thing must exist unconditioned. However, it was also necessary that there at least remain some possible account for which freedom might be possible (and could not be ruled as impossible). Thus, by virtue of the need for some conditioning while maintaining freedom as a necessary assumption (however unknowable) the moral law steps in to provide causality in the noumenal world. Theoretical reason only described the possibility of a cause of nature (dependent upon principles of possible experience). It left open the possibility of an "uncaused" cause; moreover, in our practical use of reason, we see that the moral law is the equivalent to a positive account of freedom, in that the moral law encompasses the will to determine itself autonomously. The use of the credential here makes it unnecessary to try and justify the existence or validity of the moral law outside the means of deduction through theoretical reason.

Thus, Kant presents the moral law as entailing a priori law of causality as it applies to our pure practical reason. Further, it holds that pure practical reason "fills the void" where theoretical reason left off. From this then we are "warranted" in assessing the moral law as the noumenal cause of the human being (rational agent) in the sensible world (180). This is so, because the idea of causality (in general) prior to being applied to any object (sensible, intelligible) not dependent on sense impression (since it as an idea). Kant designates this definition then as a means of authorization for the following, "...to make no other use of it than with regard to the moral law which determines its reality, that is, only a practical use." Practical reason then employs this through the moral law - which in itself entails a law of causality. What more can be said about causality? Kant believes that the idea of causality is essentially absent any empirical origin and we are authorized in our practical sense necessary to consider rational agents in possession of a free-will. Interestingly, Kant also produced a fact - that the concept of a pure will exists a priori "given" through the moral law, which accounts then for a causal determination of one's will. Since the will contains the very concept of causality in itself, the pure will entails that it must be one in which freedom is the only cause. The concept of cause has its origins solely in the grounds of the pure understanding, and likewise, it itself is not dependent on sense impressions. From here, Kant considers himself warranted to apply the concept (practically) to objects of the noumenal world, but must restrict its use from the theoretical reason (184).

This warrant though is only possible by positing certain assumptions about causality in general. Kant differentiates his concept of causality on grounds that it must contain in itself necessity. Kant says that when we apply the category of the understanding to sense impressions, this is the means for which any experience is possible. For the category of causality, it follows then that in order for any such experience to have any meaning then causality must also contain within itself "necessity." If we revoke necessity then there is no possibility of experience insofar as causality is concerned (183). Kant goes further though in saying that this allows him to deduce the a priori origins of causality (in opposition to Hume) (183). Since the concept of causality is then an a priori concept of the pure understanding - there is no objection (from reason) to apply it to the noumenal in order to practically determine a noumenal causality onto the sensible. However - he notes that this is not for the sake of generating any cognizable claims through theoretical reason, and such that because causality is not dependent upon empirical grounds, it can justifiably be used in practical reason for determining a noumenal cause (184).

Through necessity in causality, Kant sees himself authorized to apply (by virtue of its 'pure' origins) and construct a connection between freedom as necessary and objectively true for beings in the intelligible world, for which then it must be connected to the moral law as its determining ground (185). This solution, rather than theoretical deduction, avoids the problems in the latter by making no changes in our theoretical understanding of the idea of freedom of the will or the moral law itself. The objective reality of the moral law can thus be determined through its necessary connection with the idea of freedom, which in turn must be the case as long as we have to assume there is a free-will. Kant has attempted to make a unique argument to try and resettle his notorious circular problem. In this version, he tries to prove the objective moral law through a warrant that allows him to use the a priori category of causality in the pure understanding to apply to concepts in the noumenal, and thus makes it necessarily so that the moral law is the determining ground of the free-will.

Source: Critique of Practical Reason, Immanual Kant.