Abstract
Aristotle's essentialism is generally recognized as involving a distinction between what belongs to something _in itself (kath' hauto) and what belongs to it _accidentally (kata sumbebekos). But he distinguishes two relevant senses of "_in itself"; the first referring to what belongs to something in _what it is, the second referring to such attributes as: odd to number, male to animal, curved to line, and white to surface. I set out these distinctions, and argue that Aristotle counts the second class of _in itself attributes as being just as essential to the individual substances to which they belong as the first