We cannot prove by pure or theoretical reason (as Wolff tried to do) that the individual soul is immortal, or that the will is free, or that God exists; but neither can we by pure reason disprove these beliefs (as some skeptics thought to do). Reason and the categories are equipped to deal only with phenomena or appearances, external or internal; we cannot apply them to the thing-in-itself—the reality behind sensations or the soul behind ideas.
