Full Idea
Locke defines real essence as the cause of the observable qualities, and then argues that this internal constitution is not what answers the 'what is it?' question, because species is only determined by outward appearance, i.e. by nominal essence.
Gist of Idea
Real essence explains observable qualities, but not what kind of thing it is
Source
report of John Locke (Essay Conc Human Understanding (2nd Ed) [1694]) by Jan-Erik Jones - Real Essence §2
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.5
A Reaction
Helpful. This explains why sortal essentialism and essentialism based on kinds is misguided.
Related Idea
Idea 16028 Lockean real essence makes a thing what it is, and produces its observable qualities [Locke, by Jones,J-E]