Full Idea
For Aristotle, the essential properties of an object are those which are retained by it during any change through which the object remains identifiable; and they are the properties which are most important in our scientific knowledge of it.
Gist of Idea
Aristotelian essence is retained with identity through change, and bases our scientific knowledge
Source
report of Aristotle (Metaphysics [c.324 BCE]) by Irving M. Copi - Essence and Accident p.712
Book Reference
-: 'Journal of Philosophy' [-], p.712
A Reaction
This pioneering thought of Copi's (at least, he was a pioneer in that he read Aristotle properly) strikes me as the key to understanding the concept of essence.