A mind at liberty to reflect on its own observations, if it produce nothing useful to the world, seldom fails of entertainment to itself.

In 1734 he was appointed Bishop of Cloyne in Ireland a position he was to hold until his death. He takes heat as an example of a secondary quality. In 1721/2 he was made Dean of Dromore and in 1724 Dean of Derry.

In this book Berkeley's views were represented by Philonous (Greek: 'lover of mind') while Hylas (Greek: 'matter') embodies the Irish thinker’s opponents in particular John Locke. Interest in Berkeley's work increased after World War II because he tackled many of the issues of paramount interest to philosophy in the 20th century such as the problems of perception the difference between primary and secondary qualities and the importance of language.