Linguistics, often defined as 'the scientific study of language', is a b road term covering a wide range of different disciplines. The traditional 'core' areas of the subject deal with the structure of human languages in terms of how speech sounds combine to form syllables and words (phonetics and phonology), how words combine into meaningful utterances such as sentences and phrases (syntax and morphology), and how we extract meaning from utterances we read or hear used by other people (semantics and pragmatics). But beyond this, linguists are also interested in matters such as how languages evolve and change over time, how they are learned by children and by adults, how languages are used in social settings, the historical and contemporary relationships between languages, the roles of language in nation-building and identity marking, the development of writing systems, how the brain processes speech and language, how communication is possible when speech and language are impaired, and documenting endangered languages before they disappear.