Study of the nature and structure of language. It traditionally encompasses semantics, syntax, and phonology. Synchronic linguistic studies aim to describe a language as it exists at a given time; diachronic studies trace a language's historical development. Greek philosophers in the 5th century BC who debated the origins of human language were the first in the West to be concerned with linguistic theory. The first complete Greek grammar, written by Dionysus Thrax in the 1st century BC, was a model for Roman grammarians, whose work led to the medieval and Renaissance vernacular grammars.
With the rise of historical linguistics in the 19th century, linguistics became a science. In the late 19th and early 20th centuries Ferdinand de Saussure established the structuralist school of linguistics (see structuralism), which analyzed actual speech to learn about the underlying structure of language. In the 1950s Noam Chomsky challenged the structuralist program, arguing that linguistics should study native speakers' unconscious knowledge of their language (competence), not the language they actually produce (performance). His general approach, known as transformational generative grammar, was extensively revised in subsequent decades as the extended standard theory, the principles-and-parameters (government-binding) approach, and the minimalist program. Other grammatical theories developed from the 1960s were generalized phrase structure grammar, lexical-functional grammar, relational grammar, and cognitive grammar. Chomsky's emphasis on linguistic competence greatly stimulated the development of the related disciplines of psycholinguistics and neurolinguistics. Other related fields are anthropological linguistics, computational linguistics, mathematical linguistics, sociolinguistics, and the philosophy of language.