At this point of the argument Kant established the sufficient results to determ- ine the moral law’s necessary condition positively. So far this condition has only been determined negatively (Problem 1). The fourth, and last, theorem of the second Critique provides the positive determination. Unfortunately, in contrast to the previous theorems, Kant does not formulate his fourth theorem through a single proposition. What Kant aims to prove here can be understood through the following quote:
[A]utonomy of pure practical reason, that is, freedom, [...] is itself the formal condition of all maxims, under which alone they can accord with the supreme practical law. [Kan96a, 5:33]
First of all, in the above quote Kant states that the concept of autonomy is the necessary condition through which a being can be determined in accord- ance with the fundamental law. Furthermore, the above quote shows that the concept of ‘autonomy’ must be equated with the concept of ‘freedom’.31 The concept of autonomy is defined by Kant as follows:
Autonomy of the will is the sole principle of all moral laws [...] [and] the sole principle of morality consists in independence of all matter of the law [...] and at the same time in the determination of choice through the mere form of giving universal law that a maxim must be capable of. [Kan96a, 5:33]
Recall though that this “independence, however, is freedom in the negative sense”, moreover “whereas this lawgiving of its own on the part of pure and, as such, practical reason is freedom in the positive sense” [Kan96a, 5:33]. Hence, it can be concluded that the concept of autonomy is the concept of freedom defined as a conjunction of the concepts of positive and negative freedom.
Definition 3.19. (Positive Freedom) Positive freedom is the idea of a
being capable of lawgiving of its own. KL
Definition 3.20. (Freedom) The concept of freedom is defined as the
conjunction of the concept of negative freedom and positive freedom. KL 3.10.1 Theorem IV - the Argument
Kant’s fourth theorem can be reformulated as follows:
Theorem 4. The concept of freedom is the (a priori) necessary condition
through which a human will can be determined by the moral law, that is, through which a being’s maxims can accord with the moral law.
31
To enhance readability I will omit explicit usage of the term ‘autonomy’ and consistently use the term ‘freedom’ instead.
The proof of this claim is provided by the conjunction of the following res- ults. Firstly, Problem1showed that, for a will to be determined by a practical law, it needs to be determined independently from natural causality. This in- dependence is nothing but the concept of freedom in itsnegative sense. Hence, it can be concluded that a will can be determined by a practical law, only if it is negatively free. Secondly, Theorem 3 and FLoP showed that, for a rational being’s will to be determined by a practical law, that being must regard itself as capable of giving universal law through its maxims; that is, it must regard his maxims as fit for universal lawgiving. This idea of ‘universal lawgiving of its own’ however is nothing but the concept of freedom in its positive sense. Hence, a will can be determined by practical law, only if it is both negatively and positively free. The conjunction of negative and positive freedom however is the concept of freedom and it can therefore be concluded that a will can be determined by practical law, only if that will has the property of freedom. The above result is established for rational beings in general. In combination with Corollary 2 the above result implies the following: A will of a human being can be determined by the moral law only if that will is free. (The structured proof of Theorem 4can be found in the Appendix at A7.)
The proof of Kant’s fourth theorem finishes the practical necessity argument:
Proposition6. (The Practical Necessity Argument) The concept
of freedom is the necessary condition of the possibility of the moral law as a synthetic a priori proposition; that is, the concept of freedom is the necessary condition of a human will in order to be (immediately) determinable by the moral law.
Proof: Follows immediately from Theorem4.
This finishes the elaboration of the necessity argument as found in the Cri- tique of Practical Reason. This chapter treated Kant’s argument for arriving at a positive formulation of the moral law (section 3.5 and 3.7) and the argu- ment for the concept of freedom as the necessary condition of the moral law (section 3.6 and 3.10). Moreover, up till now Kant’s argument has been es- tablished completely a priori (section 3.9). There are still two arguments left: The possibility argument and the objective validity argument. The former will be treated in the next chapter.
Chapter 4
The Possibility Argument
In the previous chapter I have shown Kant’s derivation of the moral law and the proof of the concept of freedom as this law’s necessary condition (The- orem 4). If my interpretation is correct, Kant did not only provide a positive determination of the fundamental law of pure reason (FLoP), he also showed that pure reason is practical because it provides an a priori determining ground (Corollary2). Although we know that freedom is a necessary condition for the moral law, we do not know whether it can be the law’s sufficient condition as well, that is, whether the concept of freedom is sufficient to generate the moral law as its consequence. To prove this is to prove that freedom is the moral law’s ground. In this chapter I will provide an interpretation of, what I have called, the possibility argument.1 Let us first recall what needs to be established:
The Possibility Argument. A transcendental argument needs to show
which of φ’s necessary conditions ψ1, ..., ψn form its ground ψ∗. That ψ∗ is
φ’s ground is accomplished by (i) showing that ψ∗ is (a priori) possible and (ii) by showing thatψ∗ is sufficient to generate φas its consequence.
In relation to the Critique of Practical Reason the possibility argument can be reformulated as follows:
Postulate 9. The concept of freedom is the ground of the moral lawif and
only if (1) it is possible as concept as such and (2) it is sufficient to generate KL the moral law as its consequence.
1
Both the possibility and objective validity argument, as encountered in the second Critique, are substantially shorter than Kant’s necessity argument. Moreover, Kant provides both arguments (almost simultaneously) in section I ‘On the deduction of the principles of pure practical reason’ of chapter I of the Analytic (5:42 - 5:50). The arguments for the possibility of freedom as a ground and the concept’s objective validity, though, are essentially different. In order to enhance readability, I have decided to treat these two steps in two separate chapters.
Some of the premisses used in the possibility argument have already been proved in the previous chapter. I will omit explicit treatment of these argu- ments here, but only refer to them when necessary. Section 4.2 will be spend on Kant’s argument for part (1) of Postulate9. Section 4.3 will consist of the proof for part (2) of Postulate 9. Let us first consider a possible objection to the possibility argument.