Full Idea
Referential Opacity says you cannot preserve truth if you substitute one referring term for another ('Oedipus desires Jocasta', 'Oedipus desires his mother').
Gist of Idea
Referential Opacity says truth is lost when you substitute one referring term ('mother') for another ('Jocasta')
Source
Georges Rey (Contemporary Philosophy of Mind [1997], 2.5.6)
Book Reference
Rey,Georges: 'Contemporary Philosophy of Mind' [Blackwell 1997], p.58
A Reaction
….That is, in the context of expressing a propositional attitude. 'Oedipus desired his mother' was true. This idea requires some ignorance on the part of the person expressing the thought.