Descartes who said, "I think, therefore I am" (4)
I believe the answer is:
rene
'descartes who said i think therefore i am' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rene that I've seen before include "-- Magritte, artist" , "- Descartes, French mathematician" , "- Lalique, glass artist" .)