Almost all who write on Collier note a striking similarity between a short passage in his Clavis Universalis and the famous claim that esse is percipi in Berkeley's Principles. This essay explores that similarity in more detail than has been done before. The comparison forces us to address an issue about the nature of passivity in Berkeley's theory of mind. Two interpretations consistent with the text are offered and one is favoured on the grounds that it makes some of Berkeley's arguments more plausible. The idealisms of Berkeley and Collier are shown to have a common source
