Term used by Hume in the first Enquiry for a priori knowledge: ‘All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact’ (Enquiry Concerning Human Understanding, iv). The term reflects the belief that anything that can be known a priori must be internal to the mind, and hence transparent to us. See also demonstration, Hume’s fork, matter of fact.