The term natural language is used to distinguish Languages spoken and signed (by hand signals and facial expressions) by humans for general-purpose communication from constructs such as writing, computer-programming languages or the languages used in the study of formal logic, especially mathematical logic. In the philosophy of language, the term ordinary language is sometimes used as synonymous with natural (as opposed to mathematical or logical) language. Natural language is also considered a field of weak artificial intelligence. The term has been adopted to describe computer input terms and language modeled after or based on natural human languages rather than the artificial syntax and terms of computer languages, particularly in the areas of search engines or search functions.

Additionally, the indigenous Sign language of the world merit inclusion as natural languages owing to extensive linguistic analysis in the latter 20th century confirming their unique and consistent grammar, syntax, rules and visual logic dramatically unlike the spoken languages of the nations or geographic regions in which they arose. American, French, and British Sign Languages are the best documented examples in the literature.

=Constructed languages=

Beside ethnic languages constructed languages such as Esperanto that have evolved to the point of having native speakers may also be considered natural languages. (There are estimated to be 200-2000 Native Esperanto speakers; the number of persons fluent in Esperanto is much larger.)

=Written languages=

Written languages are not considered natural languages because until very recently, most people could neither read nor write but were nonetheless fluent speakers of at least some spoken or signed language. Also, people pick up natural languages spontaneously as children, but have to be taught to read and write.

=Computer science=

Natural languages are deemed to be unsuitable for programming languages simply because they have a vast vocabulary that can be deemed infinite, complex grammatical rules and a sense of ambiguity surrounding them. Take English language and French language, for example. It takes many years to completely master a language, and this would have been a waste of time when dealing with computing - learning a simple yet efficient embedded language is deemed much easier.

= See also =