Full Idea
When criticising the scholastic account of the explanation of qualities, Locke typically refrains from invoking real essences, and instead talks about primary, secondary and tertiary qualities.
Gist of Idea
To explain qualities, Locke invokes primary and secondary qualities, not real essences
Source
report of John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.08.10-26) by Jan-Erik Jones - Real Essence §2
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.6
A Reaction
This is the good empiricists' response to attempts to explain by means of essences - that we must stick to what is 'nearer the surface' and more knowable, only distinguishing which bits match the reality of the object.