Full Idea
In his 'shade of blue' example, Hume is (sensibly) endorsing a type of reasoning - interpolation - that is widely used by rational thinkers. Too bad that interpolation and extrapolation are incurably invalid.
Clarification
Hume admits he might know a shade of blue he had never experienced
Gist of Idea
Hume allows interpolation, even though it and extrapolation are not actually valid
Source
George Molnar (Powers [1998], 7.2.3)
Book Reference
Molnar,George: 'Powers: a study in metaphysics', ed/tr. Mumford,Stephen [OUP 2003], p.123
A Reaction
Interpolation and extrapolation are two aspects of inductive reasoning which contribute to our notion of best explanation. Empiricism has to allow at least some knowledge which goes beyond strict direct experience.
Related Ideas
Idea 23421 If a person had a gap in their experience of blue shades, they could imaginatively fill it in [Hume]
Idea 5572 Reason has logical and transcendental faculties [Kant]