Full Idea
An individual essence of an object x is a set of properties I which satisfies the following conditions: i. every property P in I is an essential property of x; ii. it is not possible that some object y distinct from x has every member of I.
Gist of Idea
An individual essence is a set of essential properties which only that object can have
Source
Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
Book Reference
Forbes,Graeme: 'The Metaphysics of Modality' [OUP 1985], p.99
A Reaction
I am coming to the view that stable natural kinds (like electrons or gold) do not have individual essences, but complex kinds (like tigers or tables) do. The view is based on the idea that explanatory power is what individuates an essence.