onset syllable onset of voicing glottalization opacity constraint specified subject condition opaque context opaque vs transparent context opaque vs transparent context [Lat. opacus ‘shady, dark’]

Contexts whose truth values are influenced by the free substitutability of expressions with the same extension are ‘referentially opaque’ (or ‘oblique’) (Quine 1960:141) in contrast to ‘transparent’ contexts. In the following example from Quine (1953:143), an opaque context is created by the use of the modal adverb necessarily. The statement It is necessarily the case that 9 is greater than 7 is true, while the statement It is necessarily the case that the number of planets is greater than 7 is false, although both expressions 9 and the number of planets have the same extension, namely the number 9. Other opaque contexts in which two expressions with an identical extension or meaning (i.e. denotation, see Frege 1892) and a different sense ( intension) cannot be freely substituted are contexts of knowledge and belief, that is, contexts of ‘propositional attitudes’ which are set by verbs such as know, believe, fear ( intensional context). The context it is true that S is an example of a transparent context.