Ever since I learned the phrase "I think therefore I am" I have liked Descartes.
Without knowing anything else about him, I am grateful for knowing that there's someone else out there who's wondered about the certainty of their senses--because I've gone down that pathway and was scared and bewildered when I couldn't think of a good answer to the problem. I've since found a solution that satisfies me and I may go into it some other time.
And, like Xeno said, Descartes' strongest argument is the one he is most famous for, and the one I like him for.
Yet I will admit that up until I posted the Descartes link, I hadn't actually read anything by him (except for some on that page), and up to the present I have read nothing more by him. I also have to agree that, when he goes into his spiel about the conception of the thing being the proof of its existence, I get a little lost. After all, just because I can conceive of a ten-legged purple polka-dotted lizard doesn't mean one exists. So if he means it in that sense, I can't agree.
It's possible there are other explanations that can hold up Descartes' claim, but I'm not real sure about them, and, frankly, I'd rather deal with the other issue of his that Xeno dealt with.
"To which I added that, since I knew some perfections which I did not possess, I was not the only being who existed, but that there must of necessity be some other being, more perfect, on whom I depended, and from whom I had acquired all that I possessed; for if I had existed alone and independent of all other, so that I had of myself all this little whereby I participated in the Perfect Being, I should have been able to have in myself all those other qualities which I knew myself to lack, and so to be infinite, eternal, immutable, omniscient, almighty--in fine, to possess all the perfections which I could observe in God."
As Xeno put it,
"In other words, God taught him everything he knows, and if he had NOT learned all this good stuff from God, then he himself must in fact be God, because he would somehow have attained perfection merely by being able to conceive of it without help. Since he's clearly not God, God exists."
I have a different take on this paragraph. I would restate Descartes this way: I must exist because I'm sitting here thinking; whether physical body or spirit or mere figment of someone's imagination, I've got a consciousness floating around and that exists. Since I exist, yet find myself questioning, ignorant, and looking for answers, I must not be omniscient. I can't do just anything so I'm not all-powerful, and my memory doesn't go on forever so it would seem I have a definite beginning, therefore, not eternal--finite rather than infinite. If this is all true, I'm not independent, self-sustaining, or whatever word you want to use. The only alternative to being independent is dependent. But on what? On something, somewhere, or someone who is, in fact, independent. That's God. Since something (me) can't come from nothing, God must exist.
I can't say for sure this is what Descartes is saying; I don't claim to understand everything I read (especially with the murderous way he writes--if you can make him out better, I commend you) but it sounds like it's approximately what he's saying to me. If it isn't what he's saying and it's not what he believes then I guess I think differently from him because the previous paragraph is not just what I think he's saying, but also my own personal belief. Also, when he says that God is "from whom I had acquired all that I possessed," I don't think he necessarily means every thought in his head was put there directly by God, but more along the lines that God put in him the ability to think. At least--again--it is what I would argue; whether or not it is what he actually means I can't be sure. But I think it fits.
Well, this is long, and I apologize for taking so long to get it up; there is no real excuse, except my difficulty with Descartes' writing style and my unfortunate tendency to procrastinate (something I am trying to improve upon).
I look forward to seeing what else you write, Xeno. I've tended to fancy myself of a philosophical mind, but after dealing with just a little of what some of these philosopher-types can come up with, I tend to want to rethink that assumption. :) But I still like the subject--at least a venture into the basics, because I think it can be important, or at least very useful.