Full Idea
The original Humean suggestion was that lawlike statements must contain only purely qualitative predicates - that is, predicates which do not require in a statement of their meaning a reference to any particular object or spatio-temporal location.
Gist of Idea
Originally Humeans based lawlike statements on pure qualities, without particulars
Source
Harré,R./Madden,E.H. (Causal Powers [1975], 2.II)
Book Reference
Harré,R/Madden,E.H.: 'Causal Powers: A Theory of Natural Necessity' [Blackwell 1975], p.30
A Reaction
Harré and Madden are keen to promote particulars (with powers) as the foundation of scientific theory, and I agree with them. It strikes me as quite elementary that generalisations arise from particulars, so can't fundamentally explain them.