In the way Descartes uses “thought”, it is entire possible that all perceptions are merely thoughts: we could just be imagining, dreaming, hallucinating, all the things that we “perceive“. — Pfhorrest

Actually, this is precisely the way Descartes uses “thought”, to wit, from P.P., 1,9:

“....I take the word ‘thought’ to cover everything that we are aware of as happening within us, and it counts as ‘thought’ because we are aware of it. That includes not only understanding, willing and imagining, but also sensory awareness....”

Conspicuously missing from the list is experience, and while experience is certainly something that happens within us, it is always a consequence of thought, and not a necessary condition for it. Not to mention the glaring redundancy in awareness of experience.

This is just quibbling over phrasing now. When I speak of “experience” I mean something like Descartes probably means by “awareness”, including sensory, but also awareness of the goings-on in our own minds.

Perhaps. But one person’s quibbling can be another person’s dialectical precision.

But it doesn’t really matter, insofar as your “I experience something, therefore I and that something exist”, while certainly true, always and inevitably reduces to his “I think therefore I am”.

It doesn’t reduce to it, it extends it.

Yes, it might, much the same as, say, rocket engines extend the principle of cause and effect.