'Three Dialogues between Hylas and Philonous ' Summary

In The First Dialogue, Hylas expresses his disdain for skepticism, adding that he has heard Philonous to have "maintained the most extravagant opinion that ever entered into the mind of man, to wit, that there is no such thing as material substance in the world." Philonous argues that it is actually Hylas who is the skeptic and that he can prove it. Thus, a philosophical battle of wit begins.

Philonous questions Hylas systematically regarding what humans know of the world, first examining secondary qualities, such as heat, to show that such qualities do not exist outside the individual mind. He then moves on to primary qualities such as extension and shape, and likewise argues that they, too, are dependent entirely on one's perception and perspective (e.g., From a distance, a great mountain appears to be small, and the shape of a thing may change dramatically under a microscope: "You may at any time make the experiment, by looking with one eye bare, and with the other through a microscope").

Hylas's view of matter (which has its origin in the Platonic theory of forms , or abstract entities that exist outside of the sensible world) is systematically destroyed by Philonous (Berkeley). The basic argument is that because matter is only known to us by its sensible qualities, it is impossible to describe or even imagine matter without these qualities. For in the absence of sensible qualities, matter, by definition, loses its essential qualities.

Berkeley's argument goes further: sensible qualities are not inherent in matter. Rather, they are ascribed and understood by the mind. Color, sound, temperature and even shape are qualities entirely dependent on a mind. Indeed, without a "mind," it becomes impossible to imagine "matter." The answer to the question, "If a tree falls in the forest and no mind is present, does it make a noise?" is answered by Berkeley's immaterialism: There is no tree, other than either the sense-data or the bundle of perceptions of which it is made up. However, God is always perceiving everything. In other words, there is always a mind present. A human (and thus a human mind) need not be present for the tree to make a sound, for the mind of God is always present, or so Berkeley argues. It is this mind of God that gives sensible qualities to matter, not matter itself.