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.
How did he arrive at this conclusion?
Descartes concludes that he can be certain that he exists because he thinks.
But in what form?
He perceives his body through the use of the senses.
Does he explain how the senses connect to thought?
Descartes proceeds to construct a system of knowledge, discarding perception as unreliable and, instead, admitting only deduction as a method.

Question: Did he have any other philosophical theories?
Self-contained rewrite: Did René Descartes have any other philosophical theories, besides admitting only deduction as a method?