 Clearly, this line of thought is not immune to criticism. Our feeling of moral constraint might be explained in terms of a Freudian super-ego, for instance. But it enables us to see why Kant thought that moral awareness—unlike any other sort of experience—gives us a practical certainty of our freedom, being “a fact in which pure reason in us proves itself actually practical” (5:42). (“Practical certainty” because it is not knowledge of the same sort as empirical and scientific knowledge.) At the same time, if Kant is right that only the Categorical Imperative reveals those ways of acting that we can justify to others, then we can see why he claims, “freedom and unconditional practical law reciprocally imply each other” (5:29f).