Full Idea
Reference via sense solves Frege's four puzzles, of the informativeness of identity statements, the failure of substitutivity in attitude contexts, of negative existentials, and the truth-value of statements using nondenoting singular terms.
Gist of Idea
Frege's 'sense' solves four tricky puzzles
Source
Nathan Salmon (Reference and Essence (1st edn) [1981], 1.1.1)
Book Reference
Salmon,Nathan: 'Reference and Essence (2nd ed)' [Prometheus 2005], p.11
A Reaction
These must then be compared with Kripke's three puzzles about referring via sense, and the whole debate is then spread before us.