Full Idea
A standard of similarity is in some sense innate. The spacing of qualities (such as red, pink and blue) can be explored and mapped in the laboratory by experiments. They are needed for all learning.
Gist of Idea
Standards of similarity are innate, and the spacing of qualities such as colours can be mapped
Source
Willard Quine (Natural Kinds [1969], p.123)
Book Reference
Orenstein,Alex: 'W.V. Quine' [Princeton 2002], p.123
A Reaction
This reasserts Hume's original point in more scientific terms. It is one of the undeniable facts about our perceptions of qualities and properties, no matter how platonist your view of universals may be.