The field of linguistics both borrows from and lends its own theories and methods to other disciplines. Linguistic theories and methods are also used in other fields of study. These overlapping interests have led to the creation of several cross-disciplinary fields.
Sociolinguistics is the study of patterns and variations in language within a society or community. In other words, it is the study of language in relation to social factors (e.g., social class, region, age, sex, national identity, rank). We can distinguish the speaker from his speaking (e.g., the Scottish pronounce the phoneme /r/ in words like car). Other sociolinguists focus on what happens when speakers of different languages interact. The goal of sociolinguistics is to understand communicative competence--what people need to know to use the appropriate language for a given social setting.
II. Psycholinguistics :
Psycholinguistics merges the fields of psychology and linguistics to study how people process language and how language use is related to underlying mental processes.
Put differently, it is the study of the cognitive processes that support the acquisition and use of language. The scope of psycholinguistics includes language performance at normal circumstances and when it breaks down. Historically, the focus of most psycholinguistic studies has been on L1 acquisition, comprehension and production. But recently, the focus is on second-language acquisition. Psycholinguists also study language disorders such as aphasia (impairment of the ability to use or comprehend words) and dyslexia (impairment of the ability to make out written language).
III. Computational Linguistics :
Computational linguistics involves the use of computers to compile linguistic data, analyze languages, translate from one language to another, and develop and test models of language processing. Computers also aid in the construction of dictionaries and concordances.
IV. Applied Linguistics :
Applied linguistics employs linguistic theory and methods in teaching...