Quine's position is that of a moderate nominalist's, and some people have claimed that despite his skilled analysis of opposing views, he fails to give a credible account of what concepts really are. Here, I'd like to propose something, not entirely adopted from Quine but probably quite close. But we need to start from a bit further.
1. Quine says "universals do not exists", LPV p. 10: One may admit that there are red houses, roses and sunsets, but deny [..] that they have anything in common. The words 'houses', 'roses' and 'sunsets' are true of sundry individual entities which are houses and roses and sunsets [..] but there is not, in addition, any entity whatever, which is named by the word [..] 'househood', 'rosehood', 'sunsethood'.
and a bit later p 12: "The explanatory value of special an irreducible intermediary entities called 'meanings' is surely illusory.
2. In his popular article "The World of Universals" (in collection Problems of Philosophy, PP), Russell stated that it is exactly this "sameness" of individual houses that would be called a universal. Here, he uses 'whiteness' as an example, PP p. 95.
Does this mean that concepts as such do not exists? Surely not, but hopefully more about that once I manage to find a new copy of "Situations and attitudes" by Barwise and Perry. I managed to misplace my copy somewhere in Switzerland, Finland or Japan..