Full Idea
Nominalism is consistent with belief in individual essences, but real essentialism postulates essences as universals (quiddities). Nominalists are nearly always empiricists, though the converse may not be the case.
Clarification
A quiddity is the what-it-is of a thing
Gist of Idea
Nominalism is consistent with individual but not with universal essences
Source
David S. Oderberg (Real Essentialism [2007], 2.1)
Book Reference
Oderberg,David S.: 'Real Essentialism' [Routledge 2009], p.20
A Reaction
This is where I part company with Oderberg. I want to argue that the nominalist/individualist view is more in tune with what Aristotle believed (though he spotted a dilemma here). Only individual essences explain individual behaviour.