Linguistics is the study of human language: its form, variety, and social life. Human language may be studied from a variety of perspectives, whether as a complex behavior, as a medium for creating and embodying social meaning, or as the instantiation of a highly structured system of knowledge within the mind of the speaker (a mental grammar), which can be investigated empirically and modeled formally. Starting from the detailed description of the structural patterns found in the world’s languages, linguists seek to establish general principles governing the organization, emergence, and use of language. Research in linguistics encompasses theories of how languages vary—and fail to vary—across space and time, how grammar evolved in the species and develops in the individual, and how language is used to create and reinforce social relationships.