Full Idea
Individual essences are essential properties that are unique to them alone. ...If a set of properties is an individual essence of A, then A has the properties essentially, and no other actual or possible object actually or possibly has them.
Gist of Idea
No other object can possibly have the same individual essence as some object
Source
Penelope Mackie (How Things Might Have Been [2006], 2.1/2)
Book Reference
Mackie,Penelope: 'How Things Might Have Been' [OUP 2006], p.19
A Reaction
I'm unconvinced about this. Tigers have an essence, but individual tigers have individual essences over and above their tigerish qualities, yet the perfect identity of two tigers still seems to be possible.