Three Dialogues between Hylas and Philonous

The book’s glossary defines extension as “the property of occupying space” (95). Rene Descartes used this concept as a means of demonstrating the absolute existence of matter, and in the dialogues, Hylas likewise uses it as a counterargument against Philonous’s immaterialism.

This is Berkeley’s primary philosophical position in the text and is the view espoused by Philonous. Idealism is associated with immaterialism, which holds that matter does not have an absolute existence outside a mind that perceives it. The only things that truly exist are ideas and spirits (or minds). Idealism is one branch of empiricism, a philosophical tradition that holds that true knowledge can be gained only through direct observation. In Berkeley’s religious idealism, the bedrock of existence is the mind of God, which perceives all things.

Materialism argues that matter exists apart from sensory perception. This is the view taken by Hylas, who many scholars have noted is likely a placeholder for eminent 17th-century philosopher John Locke. Locke maintained that mind and matter are distinct entities, and that matter possessed certain primary qualities independent of sensory perception. The glossary of the book adds that materialism in modern terms takes the more radical position that only matter exists; minds (distinct from the physical brain) do not exist whatsoever.

The glossary included in the 1979 Hackett edition notes that “although Berkeley did not use many terms in a technical sense, he used quite a number of words that have become archaic, and used others in senses that have become archaic” (95). Repugnancy is an example of this. The term is frequently employed in the dialogues by both Hylas and Philonous, and some modern readers may mistake this as a term meant to suggest distaste. However, as it is used in the book, the term is synonymous with contradiction.

Secondary qualities include heat, cold, sweetness of taste, and colors. Berkeley and Locke were both in agreement that secondary qualities do not exist absolutely in objects. Primary qualities include “extension, figure, solidity, gravity, motion, and rest” (23). Berkeley disagreed with Locke that these primary qualities had an inherent existence in objects unless perceived.

This is the unobservable substance that underlies objects. The term comes from John Locke, who argued in An Essay Concerning Human Understanding:

Substance [is] nothing, but the supposed, but unknown support of those qualities, we find existing, which we imagine cannot subsist, sine re substante, without something to support them, we call that support substantia; which, according to the true import of the word, is in plain English, standing under, or upholding (Weir, Ralph. “Substance.” Internet Encyclopedia of Philosophy).

Hylas uses the term more loosely, stating, “The word substratum is used only to express in general the same thing with substance” (33). Because substratum cannot be directly observed, Philonous argues vehemently that it cannot exist.