 Aristotle begins Ζ.10 by endorsing the following principle about definitions and their parts: “a definition is an account, and every account has parts, and as the account is to the thing, so the part of the account is to the part of the thing” (1034b20–22). That is, if y is a part of a definable thing x, then the definition of x will include as a part something z that corresponds to y. Indeed, z must stand to y in the same relation that the definition of x stands in to x; that is, z is the definition of y. So, according to this principle, the definition of a thing will include the definitions of its parts.