The philosopher René Descartes made the mind-body problem a central puzzle in the 1600s by arguing that mind and body are completely separate.

Descartes argued that the physical body is made of matter and takes up space, but the mind is immaterial and has no physical form. He suggested they connect at a tiny spot in the brain called the pineal gland. This sparked a massive debate that still puzzles scientists and philosophers today. How can a completely non-physical thought, like 'I want water,' physically cause your hand to reach out and grab a glass?