Full Idea
The Slingshot argument (of Frege, Church and Gödel) assumes that if two sentences are logically equivalent, they correspond to the same thing, and what a sentence corresponds to is not changed if a singular term is replaced by a coreferring term.
Gist of Idea
The Slingshot assumes substitutions give logical equivalence, and thus identical correspondence
Source
Donald Davidson (Truth and Predication [2005], 6)
Book Reference
Davidson,Donald: 'Truth and Predication' [Belknap Harvard 2005], p.128
A Reaction
This obviously won't work for 'Oedipus thinks he ought to marry Jocasta'. Sentences correspond, I presume, to what they are about, which is often a matter of emphasis or phrasing. Hence the Slingshot sounds like nonsense to me.
Related Ideas
Idea 10750 Slingshot Argument: seems to prove that all sentences have the same truth-maker [Oliver]
Idea 17308 Explaining 'Adam ate the apple' depends on emphasis, and thus implies a contrast [Schaffer,J]