Summary

Descartes prepares to embark on his final task: proving that there is a material world. To do this, he first examines his faculty of imagination, which is what constantly leads him back to the belief in material things by presenting him with images of them. To be able to imagine something and conceive of them is not the same thing, Descartes thinks; we can easily conceive of a hundred-sided figure, and even logically demonstrate what properties it must have, but we cannot picture one before our mind’s eyes. As such, imagination is not essential to understanding, and therefore not essential to our nature as thinking, understanding things.

Descartes hypothesizes that while understanding is the mind turning towards itself, imagination is the mind turning towards the body, and in order to prove this hypothesis, Descartes turns to sense perception. He observes that feelings...