propositional opacity failure of a clause to express any particular proposition (especially due to the occurrence of pronouns or demonstratives). If having a belief about an individual involves a relation to a proposition, and if a part of the proposition is a way of representing the individual, then belief characterizations that do not indicate the believer’s way of representing the individual could be called propositionally opaque. They do not show all of the propositional elements. For example, ‘My son’s clarinet teacher believes that he should try the bass drum’ would be propositionally opaque because ‘he’ does not indicate how my son John’s teacher represents John, e.g. as his student, as my son, as the boy now playing, etc. This characterization of the example is not appropriate if propositions are as Russell conceived them, sometimes containing the individuals themselves as constituents, because then the propositional constituent (John) has been referred to. Generally, a characterization of a propositional attitude is propositionally opaque if the expressions in the embedded clause do not refer to the propositional constituents. It is propositionally transparent if the expressions in the embedded clause do so refer. As a rule, referentially opaque contexts are used in propositionally transparent attributions if the referent of a term is distinct from the corresponding propositional constituent.
See also DE DICTO, KNOWLEDGE DE RE, PROPOSITION , REFERENTIALLY TRANSPAR — EN. T.M.