structure (n.)
In its most general sense, and especially as defined by STRUCTURALIST studies of human institutions and behavior, the term applies to the main abstract characteristic of a SEMIOTIC SYSTEM. A LANGUAGE, for example, is a structure, in the sense that it is a network of interrelated UNITS, the MEANING of the parts being specifiable only with reference to the whole. In this sense, the terms ‘structure’ and ‘system’ are often synonymous (and the phrase ‘structured system’ which is sometimes encountered – as in ‘language is a structured system’ – is a tautology). More specifically, the term is used to refer to an isolatable section of this total network, as in discussion of the structure of a particular GRAMMATICAL area (e.g. TENSES, PRONOUNS), and here ‘structure’ and ‘system’ are distinguished: one might talk of the ‘structure’ of a particular ‘system’.
However, this application of the term to PARADIGMATIC relationships is not as widespread as the SYNTAGMATIC conception of ‘structure’. Here a particular sequential pattern of linguistic ELEMENTS is referred to as ‘a structure’, definable with reference to one of the various ‘structural LEVELS’ recognized in a theory, e.g. ‘PHONOLOGICAL structure’, ‘SYNTACTIC structure’, ‘MORPHOLOGICAL structure’, ‘SEMANTIC structure’. For example, CLAUSE structure can be defined in terms of STRINGS of such elements as SUBJECT, VERB and OBJECT, or NOUN PHRASES and verb phrases; SYLLABLE structure can be defined in terms of strings of CONSONANTS and VOWELS. The set of items which CONTRAST at a particular ‘place’ in a structure is then referred to as a system. This is the way in which the term is used in HALLIDAYAN linguistics, for example, where it has a special status, as the name of one of the four major CATEGORIES recognized by the theory (the others being ‘unit’, ‘system’ and ‘class’): the category of ‘structure’ accounts for the ways in which an occurrence of one syntactic unit can be made up out of occurrences of the unit below it (e.g. which kinds of GROUP structure can constitute which kinds of clause structure). In this sense, the MORPHEME has no structure, being the minimal unit in grammar. A narrower use of the term is found in the phrase structure index, sometimes used in TRANSFORMATIONAL GRAMMAR to refer to the FORMAL description of the input string to a transformational RULE – also known as a STRUCTURAL DESCRIPTION. A structure-preserving CONSTRAINT is one which imposes the condition that a CONSTITUENT can be MOVED only into another CATEGORY of the same structural type, which has been independently generated. Transformations to which this constraint applies are known as ‘structure-preserving transformations’.
