Full Idea
An essential property of an object x is a property without possessing which x could not exist.
Gist of Idea
Essential properties are those without which an object could not exist
Source
Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
Book Reference
Forbes,Graeme: 'The Metaphysics of Modality' [OUP 1985], p.97
A Reaction
This is certainly open to question. See Joan Kung's account of Aristotle on essence. I am necessarily more than eight years old (now), and couldn't exist without that property, but is the property part of my essence?