Language use varies in many dimensions. Three major dimensions are the following:
The term `lect', a back-formation from `dialect', is sometimes used to cover the notion of language variant.
Language users move around in the `variety space' defined by these three dimensions, and the `territory' in variety space which is covered by a single user is kknown as his `idiolect'.
The movement of language users along the dimensions of regional and dialect variation is relatively restricted. Few speakers command more than a couple of dialoects or languages. But, in contrast, the variation of language with different functional contexts of use is startlingly varied - formal and informal, public and private, written and spoken, professional and trade languages.
The dimension of functional variation is quite dominant, though speakers are often quite unaware of it, and respond more immediately to dialectal and sociolectal variation. Speakers tend have a language, a dialect and a sociolect which is associated with the circumstances of their birth and upbringing. But switches in language and dialect or sociolect tend to correlate closely with switches in functional context, in addition to the basic indexical function of social classification.
At the level of languages, an instructive example is English in the late 20th century. English is used by a large community of native speakers in well-to-do Western societies, who accept that they fundamentally speak the same language, though different areas are associated with different dialects, and some of these dialects have become accepted as standard languages (south-eastern educated British; mid-West American; Canadian; Australian; South African. English is also used as a native language, and non-native standard language, in ex-colonies of the British empire. English is also used as a trade language by non-native speakers, in the form of a pidgin language and, in societies for which a pidgin has become a native language in the course of two or more generations, also creole languages.
Some of these characterisations of the varieties of English point to the notion of `register', the variation of language with type of use, rather than with the origin-marking features user.
Task: Find definitions of the terms `register', `functional style', `style', `Fachsprache'.