Conversation so far:
What was one of Descartes' philosophical writings?
Descartes arrives at only a single principle: thought exists.
Thought cannot be separated from me, therefore, I exist.
Did this theory become popular?
CANNOTANSWER.

Question: How did he arrive at this conclusion?
Self-contained rewrite: How did René Descartes arrive at the conclusion that Thought cannot be separated from me, therefore, I exist??