Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication. The scientific study of language in any of its senses is called linguistics.
The approximately 3000–6000 languages that are spoken by humans today are the most salient examples, but natural languages can also be based on visual rather than auditive stimuli, for example in sign languages and written language. Codes and other kinds of artificially constructed communication systems such as those used for computer programming can also be called languages. A language in this sense is a system of signs for encoding and decoding information. The English word derives from Latin lingua, "language, tongue." This metaphoric relation between language and the tongue exists in many languages and testifies to the historical prominence of spoken languages. When used as a general concept, "language" refers to the cognitive faculty that enables humans to learn and use systems of complex communication.
The human language faculty is thought to be fundamentally different from and of much higher complexity than those of other species. Human language is highly complex in that it is based on a set of rules relating symbols to their meanings, thereby forming an infinite number of possible utterances from a finite number of elements. Language is thought to have originated when early hominids first started cooperating, adapting earlier systems of communication based on expressive signs to include a theory of other minds and shared intentionality. This development is thought to have coincided with an increase in brain volume. Language is processed in many different locations in the human brain, but especially in Broca’s and Wernicke’s areas. Humans acquire language through social interaction in early childhood, and children generally speak fluently when they are around three years old. The use of language has become deeply entrenched in human culture and, apart from being used to communicate and share information, it also has social and cultural uses, such as signifying group identity, social stratification and for social grooming and entertainment. The word "language" can also be used to describe the set of rules that makes this possible, or the set of utterances that can be produced from those rules.
All languages rely on the process of semiosis to relate a sign with a particular meaning. Spoken and signed languages contain a phonological system that governs how sounds or visual symbols are used to form sequences known as words or morphemes, and a syntactic system that governs how words and morphemes are used to form phrases and utterances. Written languages use visual symbols to represent the sounds of the spoken languages, but they still require syntactic rules that govern the production of meaning from sequences of words. Languages evolve and diversify over time, and the history of their evolution can be reconstructed by comparing modern languages to determine which traits their ancestral languages must have had for the later stages to have occurred. A group of languages that descend from a common ancestor is known as a language family. The languages that are most spoken in the world today belong to the Indo-European family, which includes languages such as English, Spanish, Russian and Hindi; the Sino-Tibetan languages, which include Mandarin Chinese, Cantonese and many others; Semitic languages, which include Arabic and Hebrew; and the Bantu languages, which include Swahili, Zulu, Xhosa and hundreds of other languages spoken throughout Africa.
The word "language" has two meanings: language as a general concept, and "a language" (a specific linguistic system, e.g. "French"). Languages other than English often have two separate words for these distinct concepts. French for example uses the word langage for language as a concept and langue as the specific instance of language.
When speaking of language as a general concept, several different definitions can be used that stress different aspects of the phenomenon.
One definition sees language primarily as the mental faculty that allows humans to undertake linguistic behaviour: to learn languages and produce and understand utterances. This definition stresses the universality of language to all humans and the biological basis of the human capacity for language as a unique development of the human brain. This view often understands language to be largely innate, for example as in Chomsky's theory of Universal Grammar or Jerry Fodor’s extreme innatist theory. These kinds of definitions are often applied by studies of language within a cognitive science framework and in neurolinguistics.
Another definition sees language as a formal system of symbols governed by grammatical rules combining particular signs with particular meanings. This definition stresses the fact that human languages can be described as closed structural systems consisting of rules that relate particular signs to particular meanings. This structuralist view of language was first introduced by Ferdinand de Saussure. Some proponents of this view of language, such as Noam Chomsky, define language as a particular set of sentences that can be generated from a particular set of rules. The structuralist viewpoint is commonly used in formal logic, semiotics, and in formal and structural theories of grammar, the most commonly used theoretical frameworks in linguistic description. In the philosophy of language these views are associated with philosophers such as Bertrand Russell, early Wittgenstein, Alfred Tarski and Gottlob Frege.