Full Idea
Frege's Puzzle: If two sentences convey different information, they have different semantic roles, so the names 'Cicero' and 'Tully' are semantically different, in which case they are referentially different - but they are not referentially different.
Clarification
'Cicero' and 'Tully' are two names for the same person
Gist of Idea
Frege's Puzzle: from different semantics we infer different reference for two names with the same reference
Source
report of Gottlob Frege (On Sense and Reference [1892]) by Kit Fine - Semantic Relationism 2.A
Book Reference
Fine,Kit: 'Semantic Relationism' [OUP 2007], p.34
A Reaction
[this is my summary of Fine's summary] Given the paradox, the question is which of these premisses should be challenged. Fregeans reject their being referentially different. Referentialists reject the different semantic roles.