Often considered to be 'the father of modern philosophy', and the greatest French philosopher, ahead of Jean-Paul Sartre.

Descartes made important contributions to Maths and Science, as well as his groundbreaking new style of philosophy.

He is seen as a dualist, because his philosophy sees mind and body as two different kinds of 'stuff'.

He saw the body as essentially a physical machine.

This raises questions about free will: how can the mind affect the body and vice versa?

His most famous phrase was 'Cogito ergo sum' 'Je pense, donc je suis'  ("I think therefore I am")

This was a conclusion to a series of thoughts he was having, where he tried to doubt everything. He realised he could doubt all sorts of his beliefs, but that he could not doubt the existence of the 'I' which was thinking (he was able to question existance and to do this, he must exist).

His views of the 'self' have interested countless philosophers. Many think that he makes an important but understandable mistake, in treating the mind like a kind of theatre which has a mental subject (the 'I' or 'me') and mental objects ('ideas'). However, philosophers have struggled to fully explain consciousness ever since.

Descartes also developed an ontological argument for God's existence.