[weikel]

Well unless your insane you accept the external world axiomatically but you can't be certain of its reality the way you can be that "you exist" it could be a big dream, elaborate simulation etc.

[discostu]

I'm way out of practice, and one must remember that most of my dealings with philosphy involved a hot chick I was trying to get to "know", pot, and Pink Floyd (never worked either... but it might have if I hadn't been such a chicken at that age). But basically that was what Descartes was doing, but he was building the axiomatic proof from the only given that exists. That's part of the fun of what he did. Most people accept the reality around them as a given, Descartes decided it was something to be proven. Which is really interesting, even if it has resulted in some of the worst sci-fi ever.

[Aquinasfan]

Well unless your insane you accept the external world axiomatically but you can't be certain of its reality the way you can be that "you exist"...

I think you just have to accept external reality period. Exactly how do you "doubt" physical sensation? I mean, I can say that I doubt the existence of my own sensations, but isn't such a statement incoherrent, contradictory and absurd since it is impossible for me not to experience my own sensations?

Some truths we know simply because they are. They are prior to logical proof because they precede ratiocination and in fact are necessary for the possibility of ratiocination.

Descartes big, fat error was to artificially and without reason to bifurcate the human person, body and mind or body and soul.

...it could be a big dream, elaborate simulation etc.

But it can't be. Our central sense tells us whether or not we are dreaming. Besides, if it were literally impossible to distinguish a dream from reality then where did the idea of "dream" come from?