Kant's Demonstration of Free Will, Or, How to Do Things with Concepts

Kant famously insists that free will is a condition of morality. The difficulty of providing a demonstration of freedom has left him vulnerable to devastating criticism: critics charge that Kant's post-Groundwork justification of morality amounts to a dogmatic assertion of morality's authority. My paper rebuts this objection, showing that Kant offers a cogent demonstration of freedom. My central claim is that the demonstration must be understood in practical rather than theoretical terms. A practical demonstration of x works by bringing x into existence, and what the demonstration of freedom brings into existence is a moral will, a will regulated by the moral law and capable of acting in accordance with it. Since to act morally is to act freely, bringing a moral will into existence actualizes our capacity for freedom and demonstrates that we possess it. To confirm the viability of such a demonstration, Kant must establish that agents can regulate their wills by practical principles, and that practical judgments are efficacious of themselves (i.e., that non-Humean motivational internalism is true). Kant, I argue, is successful on both counts.