Theoretical (or general) linguistics encompasses a number of sub-fields, such as the study of language structure (grammar) and meaning (semantics). The study of grammar encompasses morphology (formation and alteration) of words and syntax (the rules that determine the way words combine into phrases and sentences). Also a part of this field are phonology, the study of sound systems and abstract sound units, and phonetics, which is concerned with the actual properties of speech sounds (phones), non-speech sounds, and how they are produced and perceived.

Linguistics compares languages (comparative linguistics) and explores their histories, in order to find universal properties of language and to account for its development and origins (historical linguistics).

Applied linguistics puts linguistic theories into practice in areas such as foreign language teaching, speech therapy, translation and speech pathology.

Linguistic inquiry is pursued by a wide variety of specialists, who may not all be in harmonious agreement.

Contextual linguistics

Contextual linguistics may include the study of linguistics in interaction with other academic disciplines. While in core theoretical linguistics language is studied independently, the interdisciplinary areas of linguistics consider how language interacts with the rest of the world.

Sociolinguistics, anthropological linguistics, and linguistic anthropology are social sciences that consider the interactions between linguistics and society as a whole.

Psycholinguistics and neurolinguistics combine medical science and linguistics.

Other cross-disciplinary areas of linguistics include language acquisition, evolutionary linguistics, computational linguistics and cognitive science.

[edit] Applied linguistics

Theoretical linguistics is concerned with finding and describing generalities both within particular languages and among all languages. Applied linguistics takes the results of those findings and applies them to other areas. Often applied linguistics refers to the use of linguistic research in language teaching, but results of linguistic research are used in many other areas, as well.

Many areas of applied linguistics today involve the explicit use of computers. Speech synthesis and speech recognition use phonetic and phonemic knowledge to provide voice interfaces to computers. Applications of computational linguistics in machine translation, computer-assisted translation, and natural language processing are extremely fruitful areas of applied linguistics which have come to the forefront in recent years with increasing computing power. Their influence has had a great effect on theories of syntax and semantics, as modelling syntactic and semantic theories on computers constrains the theories to computable operations and provides a more rigorous mathematical basis.

Diachronic linguistics

Whereas the core of theoretical linguistics is concerned with studying languages at a particular point in time (usually the present), diachronic linguistics examines how language changes through time, sometimes over centuries. Historical linguistics enjoys both a rich history (the study of linguistics grew out of historical linguistics) and a strong theoretical foundation for the study of language change.

In universities in the United States, the non-historic perspective seems to have the upper hand. Many introductory linguistics classes, for example, cover historical linguistics only cursorily. The shift in focus to a non-historic perspective started with Saussure and became predominant with Noam Chomsky.

Explicitly historical perspectives include historical-comparative linguistics and etymology