(1956-1650) a French mathematician and philosopher famous for establishing the principle of "cogito ergo sum" (=I think, therefore I am), which means "I know that I exist because I know that I think"
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
Dictionary pictures of the day
Do you know what each of these is called?
Click on any of the pictures above to find out what it is called.