If this ghost can walk through walls, how can it hold something in its hand? Because the ghost is a nonphysical entity—that’s why it can float through walls—shouldn’t any object fall through its hands? This drawing illustrates the mind–body problem exhibited in dualistic theories of consciousness. In dualism, the mind is like a ghost: a nonphysical spirit. There is thus no way to explain how the mind can influence the body, which is a physical object.