Abstract: According to Kant, all events in nature are subject to the principle of causality. Nevertheless, free actions are possible, because freedom and the universal law of causality are compatible without contradiction. Quantum mechanics is indeterministic, i.e. it implies a violation of causality. It is shown that: 1) this indeterminism can be understood by means of a continuation of Kant’s transcendental philosophy, as it is, like determinism, just a special type of universal causality, occurring when objects are not completely determined, 2) quantum mechanical indeterminacy must not be identified with freedom, because it occurs only within the realm of sensible appearances existing in space and time, whereas freedom belongs to an intelligible substratum that is not part of the sensuous world.