1) Rene Descartes sought to find an absolute certain foundation of knowledge through using methodological doubt to question all beliefs. 2) He determined that senses can be deceiving and mathematics could be an illusion created by an evil demon. 3) Descartes concluded that the only indubitable fact is "I think, therefore I am" as the act of doubting proves one's own thinking mind exists. This establishes the basis to rebuild knowledge.

1. Rationalist Epistemology – Rene Descartes Unit 2, Part 2

4. Can we trust our senses? Look at the picture on the left. Are those lines straight or sloped? If you think they look sloped – you agree with nearly all those who look at this photo. But you’d be wrong – those lines are actually straight. Your eyes have deceived you! Look at the picture on the left. Can you count the black dots? How many are there? The answer is zero! Your eyes made you see black dots where there are none. You’ve been tricked!