Robert Paul quotes: 'The notion of “what it is to be” for a thing is so pervasive in Aristotle that it becomes formulaic: what a definition expresses is “the what-it-is-to-be” (to ti ên einai). Roman translators, vexed by this odd Greek phrase, devised a word for it, essentia, from which our “essence” descends. So, an Aristotelian definition is an account of the essence of something.' Thank you, Robert, for this. I have found a number of places where Aristotle discusses definitions in this way. But I have this, possibly mistaken, memory that somewhere Aristotle adds a reference to how a definition is necessarily about 'this' and not 'that'. It may be connected to a discussion of substance, which necessarily identifies a 'this', or I am just getting it all muddled up. Sincerely, Phil