In which discipline/field was René Descartes famous?

Descartes walks into a bar and orders a drink. When he is finished the bartender asks, "Will you have another?" Descartes says, "I think not," and POOF! he disappears.

I'm pink, therefore I'm spam 😄.

Kat, did he leave a tip?

Had to study him in uni. Definitely not want to repeat that course