The proposition Esseest percipi plays an instructively ambiguous role in Berkeley's philosophy—as well as in the history of the theory of knowledge in general. It has, for instance, been construed as a false synthetic proposition by G. E. Moore and as a convention regarding sense-data by A. J. Ayer. And it is of course incompatible with the admission of material objects existing unperceived. I cannot myself see that Berkeley's account of the formula allows us to say that he regards it exc lusively as a proposition or as a convention, and I think that to grasp the mixed way in which Berkeley employs the formula is to under-stand much about the strategy of disputes regarding perception. I base my remarks entirely on the Dialogues.