How did Immanuel Kant connect reason with free will and moral responsibility?

Immanuel Kant connected reason, free will, and moral responsibility by proposing a dualistic view of human nature that distinguishes between the phenomenal world of causal determinism and the noumenal realm of practical reason.12

For Kant, human beings are autonomous only when their actions are directed solely by rationality rather than by external factors, desires, or inclinations. He argued that to act freely is to act according to the categorical imperative—a formal principle requiring that one act only on maxims that one could simultaneously will to become a universal law. By following these universal laws, the will escapes the contingencies of the empirical world, granting the agent moral dignity.341

Kant viewed this capacity for autonomy as the foundation of moral responsibility. Because reason (the "noumenal self") is independent of the causal order, it allows agents to choose morally. While Kant acknowledged the difficulty of reconciling this inner freedom with the outward laws of causality, he maintained that freedom is an essential postulate for the moral life, enabling individuals to recognize the intrinsic value of themselves and others as rational beings.2314