The Concept of Practical Philosophy in Later Kant

Kant defines a philosopher as “the legislator of human reason” (Pure Reason, B867). The philosopher's legislation has two objects, nature and freedom, and therefore contains both the laws of nature (natural laws) and the laws of freedom (moral laws). The former determine a priori what is and comprise the system of nature; the latter determine a priori what should be and make up the system of freedom. Theoretical or speculative philosophy takes care of the former; practical philosophy takes care of the latter.

In Kant's later writings, practical philosophy is split into a “metaphysics of morals” and a “moral anthropology” (Doctrine of Right, 6:217). The former contains a priori the principles that dispose of “freedom in both the external and the internal use of choice” (Doctrine of Right, 6:214), and for that reason is also called “anthroponomy” (Doctrine of Virtue, 6:406). The latter, moral anthropology, comprises the study of subjective conditions, pertaining to human nature, that are either favorable or contrary to the execution of the laws of practical reason (Doctrine of Right, 6:217).

This distinction is a novelty relative to the first Critique. In the first Critique, Kant contrasts practical philosophy, especially pure morals, which deals with the principles that “determine action and omission a priori and make them necessary,” with anthropology, conceived as an empirical, scientific theory. He says, for example, that “the metaphysics of morals is really the pure morality, which is not grounded on any anthropology (no empirical condition)” (Pure Reason, B869–70).