I think, therefore I am

The guy who said "I think, therefore I am" was French philosopher Rene Descartes.

In his 1637 book Discourse on the Method, he argued that we should doubt every single thing around us until we have reached the ultimate level of doubt -- until "there is absolutely nothing in the world, no sky, no earth, no minds, no bodies." Who, or what, has survived this vicious onslaught of doubt? What about you, the person doing the doubting? Would you survive? To Descartes, the answer is yes. Because if you are wondering whether you exist, the act of merely thinking that is enough proof that you do, since there is an "I" while you're doing the thinking. Hence the phrase.

The next step is even crazier. Now we have established that you exist, but nothing else around you does. This is called solipsism, where one's own mind is all there is in the world. Now you've just screwed yourself over. How do you get everything back? You call God. But wait, He supposedly died in your Doubt Offensive. So you try to bring Him back by laying out a rational proof of His existence. It goes something like this: if you look at everything in the universe and try to determine its origins, everything goes up to God. For example, my blog exists because of my computer, my computer exists because of people like Jack Kilby, those people exist because of their parents, because of their parents, because of Adam and Eve, Adam and Eve exist because of God. You admit that the most perfect being is God.

But wait, how would you think of those things if you've destroyed everything with your doubt? You would have to acknowledge that there are other people out there. This is called the problem of other minds. But how would you interact with this person, how would you know he is a sentient being? Simple, if they can talk, they're sentient. This is what led Descartes to believe that animals are nothing but mere robots that don't feel pain. In fact, if you do find an animal talking, that would imply that animals are not machines, or that talking is just not a good criteria for determining sentience.

Seems pretty circular to me. Why even enter a solipsist state if you're going to essentially return to the way you were before? And how could you even be alone where you doubt everything but still think in language? Language is a social tool, made by men whom you have just obliterated with doubt, so wouldn't that negate your thinking and leave you there brain dead? Rene Descartes was a pretty loony philosopher (being an extreme mind/body dualist is another example of his bad and wrong philosophies), but he was a great mathematician.