David Hume investigated the problem of the origin of the concept of causality. Is the concept of causality truly independent of experience or is it learned from experience? Hume mistakenly attempted to derive the concept of causality from experience. He thought that causality was really based on seeing two objects that were always together in past experience. If causality is not dependent on experience, however, then it may be applied to metaphysical objects, such as an omnipotent God or an immortal soul. Kant claimed to have logically deduced how causality and other pure concepts originate from human understanding itself, not from experiencing the external world.