Kant's solution to the free-will problem relies on

A the fact that anything can happen at any time.

B the idea that causation is a scientific concept, not an ethical one, and ethics is required for freedom.

C the distinction between appearance and reality: while the observable effects of events are part of the determined order, the intelligible causes and their causal power are outside the series of empirical conditions.

D the observable reality of things in themselves: if we use advanced powers of observation, we can know reality in itself and thus be free.

E we are free from the standpoint of the realm of appearance; we are free merely by believing so.