In this chapter, Descartes gives an account of the conclusions he reached during that winter in Germany. As he recounts, there are times in one’s life where one is unsure of the correct opinion to hold, and, when in doubt, a person goes along with the most popular. However, says Descartes, his method will be the precise opposite. Instead, Descartes will “reject as being absolutely false everything in which I could suppose the slightest reason for doubt, in order to see if there did not remain after that anything in my belief which was entirely indubitable” (53).

Thus, because Descartes has committed himself to treating as false any opinion or belief that, when put into doubt, leaves the individual no longer certain of the true value of their beliefs, Descartes proceeds by doubting (or rejecting as false): 1) any knowledge gained from his senses; 2) knowledge derived by his own capacity for reasoning; and 3) the knowledge he has gained from waking life.

What is found after subjecting everything he thinks he knows to doubt, writes Descartes, is that he immediately:

became aware that, while I decided thus to think that everything was false, it followed necessarily that I who thought thus must be something; and observing that this truth: I think, therefore I am, was so certain and so evident that all the most extravagant suppositions of the sceptics were not capable of shaking it, I judged that I could accept it without scruple as the first principle of the philosophy I was seeking (53-54).