opaque (adj.)
A term used in GENERATIVE PHONOLOGY to refer to the extent to which the applications of a given RULE to a given FORM cannot be seen in the PHONETIC OUTPUT at the end of the DERIVATION. The opacity of a rule is contrasted with its TRANSPARENCY.
In the context of generative SYNTAX, opaque refers to a set of CONDITIONS specifying the grammatical CONTEXTS in which an expression cannot be FREE. For example, in the construction They believe [each other are intelligent], each other is an opaque context, and cannot be CO-INDEXED with an item outside it.
The structure is ILL FORMED because the ANAPHOR each other has to be BOUND with its GOVERNING category (the EMBEDDED TENSED CLAUSE), but there is no appropriate NP present to enable this to happen. By contrast, each other is in a transparent context in They believe [each other to be intelligent]; here, it can be co-indexed with an NP outside the clause (they).
In SEMANTICS, a (referentially) opaque or intensional context is one in which the substitution of CO-REFERENTIAL terms potentially results in a change of TRUTH VALUE. For example, John believes that – is happy is an opaque context: it is possible that John believes that George Bush is happy might be true, even while John believes that the 43rd president of the USA is happy is false, even though the terms George Bush and the 43rd president of the USA refer to the same individual. Contexts in which this sort of substitution cannot result in a change of truth value are called transparent or extensional.
A term used in NON-LINEAR PHONOLOGY, as part of the characterization of the DOMAIN within which ASSIMILATION RULES apply: in long-distance assimilations (such as VOWEL HARMONY), intervening CONSONANTS are said to be either opaque or transparent. An ‘opaque’ segment is one already characterized by the NODE or FEATURE which is being SPREAD by an assimilation rule, and thus blocks the application of the rule; a segment which permits the application of a rule is said to be ‘transparent’.
