Full Idea
Failure of substitutivity shows that the occurrence of a personal name is not purely referential.
Clarification
'Substitutivity' is swapping the names without changing the truth
Gist of Idea
Failure of substitutivity shows that a personal name is not purely referential
Source
Willard Quine (Reference and Modality [1953], §1)
Book Reference
Quine,Willard: 'From a Logical Point of View' [Harper and Row 1963], p.140
A Reaction
I don't think I understand the notion of a name being 'purely' referential, as if it somehow ceased to be a word, and was completely transparent to the named object.