Full Idea
Locke's distinction would make the 'nominal essence' the target for conceptual analysis and the 'real essence' the target for substantive metaphysics.
Gist of Idea
Maybe analysis seeks the 'nominal essence', and metaphysics seeks the 'real essence'
Source
report of John Locke (Essay Conc Human Understanding (2nd Ed) [1694]) by Stephen Mumford - Laws in Nature 08.2
Book Reference
Mumford,Stephen: 'Laws in Nature' [Routledge 2006], p.128