Language is a system of communication that enables humans to express their thoughts, feelings, and ideas through spoken or written words. It is a complex and dynamic system of symbols and rules that allows individuals to convey meaning to others and to interpret the meaning of others' communications. The vast majority of human languages have developed writing systems that allow for the recording and preservation of the sounds or signs of language.
"Language" can refer to the cognitive ability to use complex communication systems, the governing rules, or the produced utterances. All languages use semiosis to connect signs to meanings. Oral, manual, and tactile languages use phonology to form words and morphemes, and syntax to combine them into phrases and utterances.
Estimates of the number of human languages in the world vary between 5,000 and 7,000. Precise estimates depend on an arbitrary distinction established between languages and dialects. Natural languages are spoken, signed, or both; however, any language can be encoded into secondary media using auditory, visual, or tactile stimuli – for example, writing, whistling, signing, or braille. In other words, human language is modality-independent, but written or signed language is the way to inscribe or encode the natural human speech or gestures.
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 in order for the later developmental stages to occur. Language evolution and diversification involve language contact, where words, phrases, and structures are borrowed from other languages, and language change, which occurs naturally through processes such as sound changes, grammaticalization, and semantic shifts. Geographical separation and social/cultural factors such as identity formation and political division can also contribute to language diversification, resulting in the rich variety of languages and dialects we see today.