One of the deepest and most lasting legacies of Descartes’ philosophy is his thesis that mind and body are really distinct—a thesis now called “mind-body dualism.”

Philosophical theory about the nature of human beings has far reaching consequences on our understanding of various issues faced by them. Once taken as self-evident, it becomes the foundation on which knowledge gets built.

In essence, by saying that mind and matter are very different, and
dividing “the aspects of single experience into separate entities – the
fatal doctrine of Descartes…spoke of mind and body, thought and its
object, matter and mind, as though they were independent existents.”
[Berlin, 381] Unfortunately, since that time, science has proceeded in the
blind belief that he thought mind is entirely reducible to matter; he did
not. They are blatantly different things.