Berkeley's idealism consists of the following claims. Objects such as chairs, apples, mountains, and our bodies are combinations of sensible qualities. Sensible qualities and combinations of such are ideas or sensations. In the philosophical sense of ‘substance’ there is no such entity as a substance. There are minds which perceive and will: When a mind perceives it has sensations or ideas; and when a mind wills it produces or causes sensations or ideas. These claims are grounded in the ontological and (...) epistemological framework of assumptions, distinctions and arguments informing Berkeley's doctrine thatesse est percipi aut percipere.The purpose of this paper is to explore and expose the main features of that framework.What is the ontological force and import on Berkeley's claim thatesse est percipi?One influential recent suggestion1 is this: Berkeley holds that (1) material substances do not exist, (2) the analysis of sensible things yields nothing but sensible qualities, (3) minds are mental substances and (4) no sensible quality or collection of sensible qualities can exist without inhering in some substance. (shrink)