Full Idea
Whereas 'Socrates is wise' denotes a sentence, 'that Socrates is wise' denotes a proposition.
Gist of Idea
'Socrates is wise' denotes a sentence; 'that Socrates is wise' denotes a proposition
Source
George Engelbretsen (Trees, Terms and Truth [2005], 4)
Book Reference
'The Old New Logic', ed/tr. Oderberg,David S. [MIT 2005], p.46
A Reaction
In traditional parlance, 'reported speech' refers to the underlying proposition, because it does not commit to the actual words being used. As a lover of propositions (as mental events, not mysterious abstract objects), I like this.