Hylas meets Philonous walking in the garden. Hylas mentions to Philonous that he was thinking during the night about an issue, and claims that Philonous is developing a reputation for holding what appears to be a rather extraordinary position, namely that matter does not exist. After Hylas brings this out in the open, he and Philonous hold a debate that begins with the definition and nature of skepticism. Philonous argues that skepticism suggests doubt, a statement with which Hylas agrees, but then asserts that simply because someone holds an opposing view, this cannot be skepticism. Hylas is reluctant to accept this premise, and Philonous begins the real debate on whether or not matter exists outside of the mind that perceives it.

First, Philonous establishes definitions, beginning with what he calls “sensible things,” meaning material objects that can be perceived with the senses. Hylas accepts the definition, and Philonous asks whether sensible things must be perceived immediately (meaning directly), or if these things can be perceived mediately through the intervention of others. Hylas answers that these sensible things must be perceived immediately. Philonous seizes on this assertion and begins to illustrate how it is connected to his views on matter.