Full Idea
All objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact.
Gist of Idea
All objects of enquiry are Relations of Ideas, or Matters of Fact
Source
David Hume (Enquiry Conc Human Understanding [1748], IV.I.20)
Book Reference
Hume,David: 'Enquiries Conc. Human Understanding, Morals', ed/tr. Selby-Bigge/Nidditch [OUP 1975], p.25