Natural language

In the philosophy of language, a natural language (or ordinary language) is a language that is spoken, written, or signed by humans for general-purpose communication, as distinguished from formal languages  (such as computer-programming languages or the "languages" used in the study of formal logic, especially mathematical logic) and from constructed languages.

Defining natural language
Though the exact definition is debatable, natural language is often contrasted with artificial or constructed languages such as Esperanto, Latino Sine Flexione, and Occidental.

Linguists have an incomplete understanding of all aspects of the rules underlying natural languages, and these rules 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 process language. 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.

The theory of universal grammar proposes that all natural languages have certain underlying rules which constrain the structure of the specific grammar for any given language.

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' rather than a 'prescriptive' term. Thus non-standard language varieties (such as African American Vernacular English) are as natural as standard language varieties (such as Standard American English).

Native language learning
The learning of one's own native language, typically that of one's parents, normally occurs spontaneously in early human childhood and is biologically driven. A crucial role of this process is performed by the neural activity of a portion of the human brain known as Broca's area.

There are approximately 7,000 current human languages, and many, if not most seem to share certain properties, leading to the belief in the existence of Universal Grammar, as shown by generative grammar studies pioneered by the work of Noam Chomsky. Recently, it has been demonstrated that a dedicated network in the human brain (crucially involving Broca's area, a portion of the left inferior frontal gyrus), is selectively activated by complex verbal structures (but not simple ones) of those languages that meet the Universal Grammar requirements.

Origins of natural language
There is disagreement among anthropologists on when language was first used by humans (or their ancestors). Estimates range from about two million (2,000,000) years ago, during the time of Homo habilis, to as recently as forty thousand (40,000) years ago, during the time of Cro-Magnon man. However recent evidence suggests modern human language was invented or evolved in Africa prior to the dispersal of humans from Africa around 50,000 years ago. Since all people including the most isolated indigenous groups such as the Andamanese or the Tasmanian aboriginals possess language, then it must have been present in the ancestral populations in Africa before the human population split into various groups to colonize the rest of the world.

Linguistic diversity
As of early 2007, there are 6,912 known living human languages. A "living language" is simply one which is in wide use by a specific group of living people. The exact number of known living languages will vary from 5,000 to 10,000, depending generally on the precision of one's definition of "language", and in particular on how one classifies dialects. There are also many dead or extinct languages.

There is no clear distinction between a language and a dialect, notwithstanding linguist Max Weinreich's famous aphorism that "a language is a dialect with an army and navy." In other words, the distinction may hinge on political considerations as much as on cultural differences, distinctive writing systems, or degree of mutual intelligibility.

It is probably impossible to accurately enumerate the living languages because our worldwide knowledge is incomplete, and it is a "moving target", as explained in greater detail by the Ethnologue's Introduction, p. 7 - 8. With the 15th edition, the 103 newly added languages are not new but reclassified due to refinements in the definition of language.

Although widely considered an encyclopedia, the Ethnologue actually presents itself as an incomplete catalog, including only named languages that its editors are able to document. With each edition, the number of catalogued languages has grown.

Beginning with the 14th edition (2000), an attempt was made to include all known living languages. SIL used an internal 3-letter code fashioned after airport codes to identify languages. This was the precursor to the modern ISO 639-3 standard, to which SIL contributed. The standard allows for over 14,000 languages. In turn, the 15th edition was revised to conform to the pending ISO 639-3 standard.

Of the catalogued languages, 497 have been flagged as "nearly extinct" due to trends in their usage.

Per the 15th edition, 6,912 living languages are shared by over 5.7 billion speakers. (p. 15)

Taxonomy
The classification of natural languages can be performed on the basis of different underlying principles (different closeness notions, respecting different properties and relations between languages); important directions of present classifications are:
 * paying attention to the historical evolution of languages results in a genetic classification of languages&mdash;which is based on genetic relatedness of languages,
 * paying attention to the internal structure of languages (grammar) results in a typological classification of languages&mdash;which is based on similarity of one or more components of the language's grammar across languages,
 * and respecting geographical closeness and contacts between language-speaking communities results in areal groupings of languages.

The different classifications do not match each other and are not expected to, but the correlation between them is an important point for many linguistic research works. (There is a parallel to the classification of species in biological phylogenetics here: consider monophyletic vs. polyphyletic groups of species.)

The task of genetic classification belongs to the field of historical-comparative linguistics, of typological&mdash;to linguistic typology.

See also Taxonomy, and Taxonomic classification for the general idea of classification and taxonomies.

Genetic classification
The world's languages have been grouped into families of languages that are believed to have common ancestors. Some of the major families are the Indo-European languages, the Afro-Asiatic languages, the Austronesian languages, and the Sino-Tibetan languages.

The shared features of languages from one family can be due to shared ancestry. (Compare with homology in biology.)

Typological classification
An example of a typological classification is the classification of languages on the basis of the basic order of the verb, the subject and the object in a sentence into several types: SVO, SOV, VSO, and so on, languages. (English, for instance, belongs to the SVO language type.)

The shared features of languages of one type (= from one typological class) may have arisen completely independently. (Compare with analogy in biology.) Their cooccurence might be due to the universal laws governing the structure of natural languages&mdash;language universals.

Areal classification
The following language groupings can serve as some linguistically significant examples of areal linguistic units, or sprachbunds: Balkan linguistic union, or the bigger group of European languages; Caucasian languages; East Asian languages. Although the members of each group are not closely genetically related, there is a reason for them to share similar features, namely: their speakers have been in contact for a long time within a common community and the languages converged in the course of the history. These are called "areal features".

N.B.: one should be careful about the underlying classification principle for groups of languages which have apparently a geographical name: besides areal linguistic units, the taxa of the genetic classification (language families) are often given names which themselves or parts of which refer to geographical areas.

Controlled languages
Controlled natural languages are subsets of natural languages whose grammars and dictionaries have been restricted in order to reduce or eliminate both ambiguity and complexity. The purpose behind the development and implementation of a controlled natural language typically is to aid non-native speakers of a natural language in understanding it, or to ease computer processing of a natural language. An example of a widely used controlled natural language is Simplified English, which was originally developed for aerospace industry maintenance manuals.

International auxiliary languages
It has been suggested that international auxiliary languages such as Interlingua, which have native speakers, can be considered natural languages for that reason. A more substantive basis for this designation is that the vocabulary, grammar, and orthography of Interlingua are natural; they have been standardized and presented by a linguistic research body, but they predated it and are not themselves considered a product of human invention. Most experts, however, consider Interlingua to be naturalistic rather than natural. Latino Sine Flexione, a second naturalistic auxiliary language, is also natural in content but is no longer widely spoken.

Constructed languages
Constructed languages such as Esperanto that have native speakers are by some also considered natural languages. However, constructed languages, while they are clearly languages, are not generally considered natural languages. The problem is that other languages have been used to communicate and evolve in a natural way, while Esperanto has been selectively designed by Zamenhof from natural languages- not grown from the natural fluctuations in vocabulary and syntax. Nor has Esperanto been naturally "standardized" by children's natural tendency to correct for illogical grammar structures in their parent's language, which can be seen in the development of pidgin languages into creole languages (as explained by Steven Pinker in The Language Instinct). The possible exception to this are true native speakers of such languages. Unfortunately, native speakers of Esperanto usually show little interest in becoming part of the international community of Esperanto speakers when they grow up.

Natural Language Processing
Natural language processing (NLP) is a subfield of artificial intelligence and computational linguistics. It studies the problems of automated generation and understanding of natural human languages.

Natural-language-generation systems convert information from computer databases into normal-sounding human language. Natural-language-understanding systems convert samples of human language into more formal representations that are easier for computer programs to manipulate.

Modalities
Natural language manifests itself in modalities other than speech.

Sign languages
In linguistic terms, sign languages are as rich and complex as any oral language, despite the common misconception that they are not "real languages". Professional linguists have studied many sign languages and found them to have every linguistic component required to be classed as true natural languages.

Sign languages are not pantomime — in other words, signs are largely arbitrary and have no necessary visual relationship to their referent, much as most spoken language is not onomatopoeic. Nor are they a visual rendition of an oral language. They have complex grammars of their own, and can be used to discuss any topic, from the simple and concrete to the lofty and abstract.

Written languages
In a sense, written language should be distinguished from natural language. Until recently in the developed world, it was common for many people to be fluent in spoken or signed languages and yet remain illiterate; this is still the case in poor countries today. Furthermore, natural language acquisition during childhood is largely spontaneous, while literacy must usually be intentionally acquired.