Natural language

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. A natural language is any system of signs, in any form of communication, that is or was communicated and can or could be understood by human beings.

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 signed languages 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.

Defining Natural Language
Though the exact definition is debatable, natural language is often contrasted with constructed languages. Linguists as of yet have an incomplete understanding of all aspects of the rules underlying natural languages, and they are therefore objects of study. The understanding of natural languages reveals much about not only how language works (in terms of syntax, semantics, phonetics, phonology, etc), but also about how the human mind and the human brain function. In linguistic terms, 'natural language' only applies to a language that has evolved naturally, and the study of natural language primarily involves native (first language) speakers.

While grammarians, writers of dictionaries, and language policy-makers all have a certain influence on the evolution of language, their ability to influence what people think they 'ought' to say is distinct from what people actually say. Natural language applies to the latter, and is thus a 'descriptive' term. Thus non-standard language varieties (such as African American Vernacular English) are as natural as standard language varieties (such as Standard American English).

Constructed languages
Besides ethnic languages, constructed languages such as Esperanto that have evolved to the point of having native speakers are by some also considered natural languages. However, for linguistic purposes, Esperanto and other constructed languages, while they are clearly languages, are not considered natural languages. The possible exception to this are true native speakers of such languages. (There are estimated to be 200-2000 native speakers of Esperanto.)

Written languages
Written language should be distinguished from natural language. Until very recently, it was not uncommon for many people to be fluent in spoken or signed languages and yet remain illiterate. Furthermore, natural language acquisition during childhood is largely spontaneous, while literacy has to be taught.

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 and French, 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. Also, any natural language is by its very nature able to express any and all meaning (though it may take a lot of words in some situations), whereas computer languages operate within a much more limited scope.