Full Idea
The causal theory of reference is criticised for vagueness. Causal connections are ubiquitous, and there are obviously many individuals that are causally implicated in the speaker's use of a name, but they aren't all plausible candidates for the referent.
Gist of Idea
In the use of a name, many individuals are causally involved, but they aren't all the referent
Source
Robert C. Stalnaker (Reference and Necessity [1997], 4)
Book Reference
Stalnaker,Robert C.: 'Ways a World Might Be' [OUP 2003], p.175
A Reaction
This seems to be a very good objection. Among all the causal links back to some baptised object, we have to pick out the referential link, which needs a criterion.