Full Idea
We have an acceptable notion of class, or physical object, or attribute, or any other sort of object, only insofar as we have an acceptable principle of individuation for that sort of object. There is no entity without identity.
Gist of Idea
No entity without identity (which requires a principle of individuation)
Source
Willard Quine (On the Individuation of Attributes [1975], p.102)
Book Reference
Quine,Willard: 'Theories and Things' [Harvard 1981], p.102
A Reaction
Note that this is his criterion for an 'acceptable' notion. Presumably that is for science. It permits less acceptable notions which don't come up to the standard. And presumably true things can be said about the less acceptable entities.