Summary

Hylas and Philonous meet again. Hylas admits that since the last time they met he has not thought of anything else except their conversation. Despite the fact that he agrees with Philonous’s reasoning, he has not been able to shake his belief in the existence of matter. He claims that there is something deeply intuitive about the mechanistic explanation for our perceptions, where nerves in the body use motion to communicate signals to the brain, which gives rise to ideas in the soul.

Philonous asks Hylas to account for what this brain is. If it is a thing we can perceive, it must be an idea. If it is a thing which we cannot perceive but merely imagine, it must also be an idea, since all our imaginations are ideas too. More important, Hylas’s hypothesis does not explain...