Full Idea
A blind man can form no notion of colours; a deaf man of sounds. ….A Laplander or Negro has no notion of the relish of wine. ….A man of mild manners can form no idea of inveterate revenge or cruelty.
Gist of Idea
We cannot form the idea of something we haven't experienced
Source
David Hume (Enquiry Conc Human Understanding [1748], II.15)
Book Reference
Hume,David: 'Enquiries Conc. Human Understanding, Morals', ed/tr. Selby-Bigge/Nidditch [OUP 1975], p.20