René Descartes is often called the "father of modern philosophy." Born into the French aristocracy in 1596, Descartes was fascinated by mathematics, and founded the field of analytical geometry. He wanted to build a system of philosophy that was as clear and certain as mathematics. To do this, he decided that he would need to question all of his presuppositions about the world. One of the presuppositions that he doubted was whether or not he could believe that what he observed through his senses was true. Consider this passage from Descartes' Meditations (Melchart, 2007):

Part 1: Think of a time when your senses deceived you. Describe what you thought you saw, heard, or felt.