Three Dialogues between Hylas and Philonous

Three Dialogues between Hylas and Philonous is a book written by George Berkeley in 1713.

Three important concepts discussed in the Three Dialogues are perceptual relativity, the conceivability/master argument ("master argument" was coined by André Gallois ), and Berkeley's phenomenalism.

Perceptual relativity argues that the same object can appear to have different characteristics (e.g. shape) depending on the observer's perspective. Since objective features of objects cannot change without an inherent change in the object itself, shape must not be an objective feature.

Hylas and Philonous
Berkeley uses Hylas as his primary contemporary philosophical adversary. A Hylas is featured in Greek mythology and is understood to represent John Locke. In the Dialogues, the name Hylas is derived from an ancient Greek word for "matter," which Hylas argues for in the dialogue.

Using Philonous, Berkeley argues his own metaphysical views, which were first developed in his earlier book A Treatise Concerning the Principles of Human Knowledge. Philonous translates as "lover of mind."

In The First Dialogue, Hylas expresses his disdain for skepticism, adding that he has heard Philonous to have "maintained the most extravagant opinion... namely, 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 (e.g., From a distance, a great mountain appears to be small, and the shape of a thing may change dramatically under 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. Yet that was precisely Plato's argument; "actual matter" did not exist here on earth but rather in another plane or dimension, and furthermore this matter had no sensible qualities. This was the prevailing view of philosophers in Berkeley's day. His argument would prove to be a devastating attack on the nearly 2000 year old platonic view.

Berkeley's argument goes further however. Sensible qualities are not inherent in matter, rather they are ascribed and understood by the mind. Color, sound, temperature, even shape, are relative 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 one is present, does it make a noise?" is answered by Berkeley's immaterialism. 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.

In his own time Berkeley faced opposition from many philosophers who held to the Platonic view. The philosophers thought Berkeley vulgar because his own view seemed to confirm the views held by the lower classes. Roughly speaking the "common view" was that God created everything and that the things on earth were the real things. Many philosophers did not believe in God and believed matter on earth but a mere imitation of actual matter that existed in another dimension. Berkeley sided with the common view.

The philosophy presented is often misinterpreted. The criticism is that Berkeley claims that we live in an illusory world, when in fact, Berkeley advocates for the acceptance of ideas as real "things." When we refer to an object, we don't refer to a material form, but to the idea of the object that informs our senses. Berkeley doesn't propose that nothing is real, he proposes that ideas themselves comprise reality.