The Mind-Body Problem

Descartes concluded that mind and body are fundamentally different substances. The body is physical, extended in space, and mechanical. The mind is non-physical, unextended, and conscious. This position, called substance dualism, created one of philosophy's most stubborn problems.

If mind and body are completely different kinds of stuff, how do they interact? When you decide to raise your arm, how does a non-physical thought cause a physical movement? The interaction problem remains unsolved to this day.