Rene Descartes (1596-1650) was not only a philosopher but also a mathematician and scientist. As a philosopher, he used skepticism as a means of finding the truth of all. His idea was to doubt everything, and in doubting everything, anything that couldn't be doubted was definite.
"I will doubt everything that can possibly be doubted, he reasons, and if anything is left, then it will be absolutely certain." (Moore/Bruder 93) This, Descartes felt was the only way to obtain truth and knowledge. This method was to take away all the confidence in everything that was taught to us, what we sense and believe, and the things we take as being obvious. To truly determine if we know anything is for certain we must doubt it all disregarding all we knew about it before. So everything we currently believe is open to discussion and can be questioned.
Descartes' 'Method of Doubt' incorporated two well-known conjectures, a dream conjecture and the evil demon conjecture.
What the dream conjecture is, is the notion that everything that is reality might just be a dream. Adding to the dream conjecture, is the evil demon conjecture. This evil demon conjecture, in essence, is the concept that if this all [reality], is just a dream, then perhaps there is an evil demon that is deceiving our minds with these false images of reality. So, we can't assume that our bodies or that anything of our experience exists
and can be trusted to be true. For everything we know could be just a dream and not real at all and controlled by a deceiver.
No, Descartes was not out of his mind. He was aware that these two conjecture he composed sounded far-fetched. However, that was the whole point. Descartes was on a quest to find certainty in...