Critique of Practical Reason

In his previous work, Critique of Pure Reason, Kant elaborated on his reasons for believing that metaphysical or “supersensible” concepts such as God and the soul cannot be proven through abstract or “speculative” reason alone. Kant does not summarize his arguments from that Critique here. However, he does suggest that one of the reasons speculative reason has such limits is because of the Enlightenment emphasis on empiricism. In particular, Kant refers to David Hume’s argument against causality, writing that Hume “asked nothing more than that a merely subjective meaning of necessity, namely custom, be assumed in place of any objective meaning of necessity in the concept of cause, so as to deny to reason any judgment about God, freedom, and immortality” (10). Hume’s empirical philosophy holds that causal relationships can only be assumed on the basis of past experience, never directly known. If the pond always freezes in midwinter, it can be assumed that very cold weather causes the pond to freeze, but Hume would argue that this is only an assumption, not an instance of direct, empirical knowledge. Under this philosophy, God can no longer be defined as the first cause of everything, because the actual relationship between cause and effect cannot be empirically experienced. Kant argues that Hume’s claims similarly undermine traditional ideas about the existence of free will and the soul, leading to an “abyss of pure skepticism” in which human lives lose all meaning (3).

Kant’s project here and in his other works is to resolve the debate between rationalists and empiricists like Hume. Kant argues for a form of speculative reason through intuition and the use of established certainties, which he calls a priori reasoning. An example of a priori reasoning would be the statement, “I am planning to leave my apartment in an hour, so I will still be in my apartment fifteen minutes from now.” The causal relationship between the two clauses in this sentence depends on the prior knowledge that free will exists, and thus that the speaker has the power to hold to his plan. The existence of free will and its power to cause events in the world are examples of a priori knowledge.

Still, Kant does not discount empirical reasoning. Empirical reasoning plays a role in Kant’s concept of practical reason: It helps individuals to understand what specific goal the will is seeking (what Kant calls the “determining grounds” of any decision). This is what Kant means when he writes that the “matter of the will…is always empirical” (36). However, Kant does conclude that relying too heavily on empirical reason is more dangerous than relying too heavily on speculative reason. The latter can lead to “mysticism,” but Kant believes one can hold mistaken ideas like mysticism and still follow the moral law. Too much empiricism, on the other hand, can lead one to replace one’s feeling of duty toward the moral law with an “empirical interest,” valuing specific, concrete goals above the universal laws that give those goals their meaning. Also, looking at the world through the lens of pure empiricism can lead into an “abyss of pure skepticism” (3), endlessly questioning not only every metaphysical topic, but every aspect of reality and lived experience.

At the heart of Kant’s thesis in Critique of Practical Reason is his certainty that free will exists and can be proven through a priori or intuitive reasoning. Kant views all beings capable of reason as possessing autonomy (total freedom) rather than heteronomy, which he defines as the state of being controlled by external forces and circumstances. Free will cannot be empirically proven, but Kant asserts that it is self-evident (that is, safely asserted through abstract, a priori reasoning). Further, through that free will, rational beings can effect causality (change the objects around them). Kant believes that the existence of this freedom proves the objective existence of God and immortality.

The claim that all human beings possess free will does not mean that people are bound to some extent by circumstances or conditions, like social pressures, illness, poverty, and so on. In fact, Kant would view such subjective, external influences on the will as further evidence that free will exists and can effect changes. The way free will determines an individual’s course of action or desire is what Kant generally calls the “determining ground” (19). The fact such a determining ground exists and that people can use their own reason to respond to a variety of internal and external—or subjective and objective—factors is itself proof of freedom.

Nor does the existence of a universal, objective moral law contradict the existence of such freedom. In fact, Kant argues that “freedom and unconditional practical law reciprocally imply each other” (26). There are certain moral standards that Kant views as unconditional and universal, yet people can still decide whether and how to obey them. Despite the existence of free will, Kant describes the moral law in terms of “necessity” and “imperative” (18), which we are compelled to obey through a sense of “duty” (29). Everyone is conscious of this duty, but individuals remain free to choose to whether to obey. Further, even with practical reason, there can be uncertainty on how to obey the moral law. This state of uncertainty is better than an alternative existence without such freedom. Kant addresses why: “As long as human nature remains as it is, human conduct would thus be changed into mere mechanism in which, as in a puppet show, everything would gesticulate well but there would be no life in the figures” (118).

The core difference between desires and duties is that desires are subjective and conditional while moral duties are objective and unconditional. How we approach the “imperative” (18) to fulfill the moral law can be subjective and determined by an individual’s practical reason. However, desires and emotions themselves are always determined by our own conditions and the circumstances surrounding us. Kant agrees with the mainstream Enlightenment view that happiness is the universal goal of all rational beings. Happiness is therefore constantly a factor in how individuals use practical reason toward fulfilling the moral law in their own lives: “To be happy is necessarily the demand of every rational but finite being and therefore an unavoidable determining ground of its faculty of desire” (23). However, happiness cannot be a universal practical law because the ability to achieve happiness is always conditioned on empirical causes, like a person’s resources and circumstances, or on abstract reasons such as what gives them happiness. One person may be happy living the rest of their life in their hometown, for example, while someone else would only be happy with a life of travel.

The feeling of duty toward the moral law differs from the pursuit of pleasure or the avoidance of displeasure in an important way. The feeling of duty and respect for moral law that Kant argues is the true motivation behind ethical action is neither pleasurable nor displeasurable in itself. Instead, Kant remarks that “all the morality of actions is placed in their necessity from duty and from respect for the law, not from love and liking for what the actions are to produce” (67). This sense of duty is what leads people to the unconditional and universal moral law. Kant describes it:

In our times, when one hopes to have more influence on the mind through melting, tender feelings or high-flown, puffed-up pretensions, which make the heart languid instead of strengthening it, than by a dry and earnest representation of duty, which is more suited to human imperfection and to progress in goodness, it is more necessary than ever to direct attention to this method (125).

Here, Kant distances himself from the Enlightenment concept of sentimentalism, which held that emotions and emotional bonds are the basis of morality. Instead, he argues that feelings of respect and duty form a more durable basis for moral behavior.