Full Idea
According to Frege, a proper name in a modal context refers obliquely; its reference there is its usual sense.
Gist of Idea
Proper name in modal contexts refer obliquely, to their usual sense
Source
report of Gottlob Frege (On Sense and Reference [1892]) by Allan Gibbard - Contingent Identity V
Book Reference
-: 'Journal of Symbolic Logic' [-], p.203
A Reaction
[he cites the fourth page of Frege's 'Sense and Reference'] One can foresee problems with the word 'usual' here. Frege might be offering something better than Kripke does here.