Full Idea
With the triadic relation of comparative similarity, kinds can contain one another, as well as overlapping. Red and colored things can both count as kinds. Colored things all resemble one another, even though less than red things do.
Gist of Idea
Comparative similarity allows the kind 'colored' to contain the kind 'red'
Source
Willard Quine (Natural Kinds [1969], p.119)
Book Reference
Quine,Willard: 'Ontological Relativity and Other Essays' [Columbia 1969], p.119
A Reaction
[compressed] Quine claims that comparative similarity is necessary for kinds - that there be some 'foil' in a similarity - that A is more like C than B is.
Related Idea
Idea 16935 If similarity has no degrees, kinds cannot be contained within one another [Quine]