Berkeley's master argument conflates the content of a proposition with the act of entertaining that proposition.

From these stipulations he derives his most fundamental and famous claim (1) that “the existence of an idea consists in being perceived” (1710: Part I, §2) or that “their esse is percipi” (1710: Part I, §3) by the perceiving, active mind. Already here Berkeley has the means in place to cast into doubt the meaningfulness of the assumption that there might exist unperceived objects or things. This is due to his restriction of existence to what is perceivable or, even narrower, to what is perceived