Three Dialogues between Hylas and Philonous

Three Dialogues between Hylas and Philonous is a work of metaphysics published in 1713 by George Berkeley. It takes the form of a conversation between two speakers: Philonous, who voices Berkeley's own ideas, and Hylas, who defends the positions of his opponents, especially John Locke. The name Philonous suggests a lover of mind (nous), while Hylas stands for matter (hyle).

The book was written in response to the criticism Berkeley received after publishing his Treatise Concerning the Principles of Human Knowledge in 1710, which had been poorly received. He recast his ideas as a dialogue, aiming for a more accessible style and a clearer defence against specific objections. Earlier, in 1709, he had published An Essay Towards a New Theory of Vision, arguing that the proper objects of sight are not material bodies but light and colour.

The argument unfolds in stages. First, Philonous shows that secondary qualities, such as heat or colour, depend on the perceiver. Then he extends the same reasoning to primary qualities, such as extension and shape, which also vary with the observer's perspective. Finally, he argues that matter, known to us only through its sensible qualities, cannot be conceived apart from them, so the idea of a material substance existing independently of any mind is incoherent. From this follows Berkeley's immaterialism: things are collections of perceptions whose existence consists in being perceived, with God perceiving them continuously.

The work was misread from the start. Many took it as a denial of the world's reality, whereas Berkeley meant precisely to affirm that ideas constitute what is real. Its influence reaches later empiricism, the debate over perception, and the philosophy of mind.