"I think therefore I am" derives directly from it:
He found that the only thing he could not doubt,
was that he doubted. Doubting is just a
particular form of thought, so: I think therefore
I am.
I don't agree with the "therefore I am" bit, but
doubting being all that can't doubted seems
fairly solid, as regards logic. An experiential
take on it might be different. You cannot do
*anything* unless you experience -- or, no
input, no output, no stimulus, no response.
Robin