George Berkeley , also known as Bishop Berkeley, was an Irish philosopher. His primary philosophical achievement was the advancement of a theory he called "immaterialism" . This theory, summed up in his dictum, "Esse est percipi" , contends that individuals can only directly know sensations and ideas of objects, not abstractions such as "matter." His most widely-read works are A Treatise Concerning the Principles of Human Knowledge and Three Dialogues between Hylas and Philonous , in which the characters Philonous and Hylas represent Berkeley himself and his contemporary John Locke. In 1734, he published The Analyst, a critique of the foundations of calculus, which was influential in the development of mathematics.