disjunction (n.)

A term in formal logic now encountered as part of the theoretical framework of several areas in LINGUISTICS, especially SEMANTICS. It refers to the process or result of relating two PROPOSITIONS in such a way that they are in an ‘either-or’ relationship, e.g. (Either) Mary is late or John is early. With disjunction, it is usual to distinguish inclusive and exclusive interpretations: with the former, the disjunction is true if either, or both, of the propositions is true; with the latter, the disjunction is true only if one or other of the propositions is true (but not both). Under the exclusive interpretation, therefore, the above disjunction would be false, if both Mary was late and John was early; whereas, under the inclusive interpretation, the disjunction would be true.

In some GRAMMATICAL descriptions, the term is adapted to refer to a process whose primary function is to mark a relationship of contrast or comparison between STRUCTURES, using such disjunctive ITEMS as or and but. (Some approaches, such as QUIRK GRAMMAR, use the term disjunct, in a highly restricted sense, to refer to a subclass of ADVERBIALS (such as seriously, frankly, really), which contrasts with CONJUNCTS, SUBJUNCTS and ADJUNCTS on SYNTACTIC and SEMANTIC grounds.) The two disjunctions above are often referred to as the ‘exclusive or’ and the ‘inclusive or’. In GENERATIVE grammar, the notion is applied as a principle affecting the order of RULES. Disjunctive ordering is found in the use of the parenthesis NOTATION, which indicates OPTIONAL ELEMENTS. If a SEQUENCE of rules is abbreviated by using this notion (e.g. X ⇒ Y/Z(P)Q, which stands for the sequence (a) X ⇒ Y/ZPQ and (b) X ⇒ Y/ZQ), then this sequence forms a disjunctively ordered block, i.e. if (a) applies, (b) is not permitted to apply. It is distinguished from CONJUNCTIVE ordering.