Kant’s political philosophy is a branch of practical philosophy, one-half of one of the broadest divisions in Kant’s thought between practical and theoretical philosophy. Political philosophy is also to be distinguished within practical philosophy from both empirical elements and from virtue proper. The separation from virtue is treated in the next paragraph. Regarding the empirical elements, it is worth mentioning that practical philosophy, as a set of rules governing free behavior of rational beings, covers all human action in both its pure and applied (empirical, or “impure”) aspects. Pure practical philosophy, the rational elements of practical philosophy in abstraction from anything empirical, is called by Kant “metaphysics of morals” (4:388). Kant so emphasized the priority of the pure aspect of political philosophy that he wrote part of his essay “On the Common Saying: That May be Correct in Theory, but it is of No Use in Practice” in opposition to the view he associates with Hobbes that the politician need not be concerned with abstract right but only with pragmatic governance (8:289–306). Yet Kant also included the more pragmatic, impure, empirical study of human behavior as part of practical philosophy. For ethics in general, Kant called the empirical study of human beings as agents within particular cultures and with particular natural capacities “anthropology”. Some of Kant’s social philosophy fits into this rubric (See section 10).
Political philosophy is not only a branch of Kant’s practical philosophy, it strongly depends upon Kant’s core practical philosophy for its basis. Kant’s practical philosophy and the categorical imperative that governs it were intended to form the ground not only for what is thought today to be ethics proper but also for everything that broadly speaking had to do with deliberative human behavior. He defined practical philosophy as that concerned with “rules of behavior in regard to free choice”, as opposed to theoretical philosophy that concerned “the rule of knowledge” (Kant 27: 243). Practical philosophy provided rules to govern human deliberative action. The Groundwork for the Metaphysics of Morals provided Kant’s main arguments that the categorical imperative is the supreme rule for human deliberative action. In its Preface, he notes that the Groundwork is to be a preparatory book for a future Metaphysics of Morals. Twelve years later he published that Metaphysics of Morals in two parts, the “Doctrine of Right” and the “Doctrine of Virtue”. Both are equally parts of Kant’s practical philosophy, and both thus have the categorical imperative as their highest principle.
The book Metaphysics of Morals has two distinct parts: the “Doctrine of Right” and the “Doctrine of Virtue”. Kant sought to separate political rights and duties from what we might call morals in the narrow sense. He limits right by stating three conditions (6:230) that have to be met for something to be enforceable as right: first, right concerns only actions that have influence on other persons, directly or indirectly, meaning duties to the self are excluded, second right does not concern the wish but only the choice of others, meaning that not mere desires but only decisions which bring about actions are at stake, and third right does not concern the matter of the other’s act but only the form, meaning no particular desires or ends are assumed on the part of the agents. As an example of the latter he considers trade, which for right must have the form of being freely agreed by both parties but can have any matter or purpose the agents want. These criteria appear to be less rigid than Kant ultimately intends, for the term “influence” is vague enough that it might include far-reaching minor effects. They would also include under right actions even those imperfect duties that “influence” others by improving their lot, such as beneficent acts of charity. John Stuart Mill’s “harm principle” does not face this problem since it specifies that the influence to be subject to law is always negative. While Kant must include consideration of beneficent action as part of right, he does not conclude that beneficent actions are required by right but only that most are permitted by right and others violate right. His focus on free individual choice entails that any beneficent action that interferes with or usurps the recipient’s free choice is wrong (for example, improving the recipient’s property without permission as opposed to merely donating money to a fund made available to the recipient at the recipient’s discretion). In addition to these three conditions for right, Kant also offers direct contrasts between right and virtue. He thinks both relate to freedom but in different ways: right concerns outer freedom and virtue concerns inner freedom (being master of one’s own passions) (6:406–07). Right concerns acts themselves independent of the motive an agent may have for performing them, virtue concerns the proper motive for dutiful actions (6:218–221). In another formulation (6:380–81) he says that right concerns universality as a formal condition of freedom while virtue concerns a necessary end beyond the mere formality of universality, thus appearing to tie the distinction to the first two formulas of the categorical imperative in the Groundwork. In yet another he says that right concerns narrow duties and virtue wide duties (6:390). In the Feyerabend lectures, Kant notes that right is the subset of morally correct actions that are also coercible (27:1327). These various alternative formulations of the distinction would exclude imperfect duties not because imperfect duties do not “influence” others (they do) but because, as imperfect, they cannot be coerced in particular instances, since imperfect duties always allow for the moderating role of an individual’s inclinations. While these various formulations of the distinction appear to be quite different, they can in general be summarized by saying that right concerns outer action corresponding to perfect duty that affects others regardless of the individual’s internal motivations or goals.