Full Idea
Let there be a man who has sometimes seen the fundamental colours, and never the intermediate and mixed colours; it may be that by a sort of deduction he will represent those he has not seen, by their resemblance to the others.
Gist of Idea
If someone had only seen the basic colours, they could deduce the others from resemblance
Source
René Descartes (Rules for the Direction of the Mind [1628], 14)
Book Reference
Descartes,René: 'Rules for the Direction of the Mind' [Newcomb Library 2023], p.49
A Reaction
Thus Descartes solved Hume's shade of blue problem, by means of 'a sort of deduction' from resemblance, where Hume was paralysed by his need to actually experience it. Dogmatic empiricism is a false doctrine!
Related Idea
Idea 23421 If a person had a gap in their experience of blue shades, they could imaginatively fill it in [Hume]