Although maxims are central to Kant’s ethical theory, his account of them remains obscure. We can make progress towards understanding Kantian maxims by examining not only their role as the object of moral judgement but also their connection to freedom of the will and causality. This requires understanding maxims as causal laws that explain the actions that we impute to agents. In this way, they are analogous to causal laws of nature, but they are limited in scope to the agents who are responsible for them. Understanding maxims in this way explains our limited epistemic access to them and helps to clarify Kant’s account of virtue and character as well as how they mediate the relationship between practical and theoretical reason.

According to Kant each person has an empirical character, which is ultimately grounded in one’s free choice. The popular Causal Laws interpretation of empirical character holds that it consists of the causal laws governing our psychology. I argue that this reading has difficulties explaining moral change, the ‘gradual reformation’ of our empirical character: Causal laws cannot change and hence cannot be gradually reformed. I propose an alternative Causal Powers interpretation of empirical character, where our empirical character consists of our mind’s causal powers. The resulting picture of empirical character allows for moral change and Kantian weakness of will.