Full Idea
If definition is of the universal rather than of the particular, ...it begins to appear that individual material substances do not have definitions and, hence, do not have essences at all.
Gist of Idea
If definition is of universals, many individuals have no definition, and hence no essence
Source
report of Aristotle (Metaphysics [c.324 BCE], partic) by Charlotte Witt - Substance and Essence in Aristotle 5.1
Book Reference
Witt,Charlotte: 'Substance and Essence in Aristotle' [Cornell 1994], p.153
A Reaction
This is a very challenging claim against my own defence (and Witt's) of individual essences. In switching to individual essences, one has to make them unstable and variable, and lacking necessity, and hence maybe not essential.