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 considered to be natural while standard language varieties (such as Standard American English) which are more 'prescripted' can be considered to be at least somewhat artificial or constructed.
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.
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.
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)
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:
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 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.)
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—language universals.
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 natural languages are subsets of natural languages whose grammars and dictionaries have been restricted in order to reduce or eliminate both ambiguity and complexity (for instance, by cutting down on rarely used superlative or adverbial forms or irregular verbs). 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.
Constructed international auxiliary languages such as Esperanto and Interlingua (even those that have native speakers) 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 L.L. 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 parents' 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. 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 naturalistic in content but is no longer widely spoken.
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.
Ever since humans began to speak, there has been a need for humans to continue to utilize the communication form of gestural communication after age 3, when speech is difficult or impossible. Humans with normal hearing ability from birth to age 6 and thereafter, who become deaf in both ears later in their lives can still speak understandably, and therefore do not require a substantial reliance on a signed form of communication.
However, individuals who become profoundly deaf in both ears during the critical period of formation of the "speech-sound (phonemic) filter structure," in the left posterior superior temporal gyrus of their brain cannot build that structure after age 3, and definitely not normally after age 6. There was a false premise that these persons still have "natural" language in regard to gestural communication for many years. However, with the use of the most modern neuroscientific brain scanning procedure, known as the fMRI (functional MRI), where the brain's operation can now be seen directly in real-time, this premise is now known to be completely false, since these early-deafened individuals do have a significant developmental disability and lack of normal brain development in this specific area that processes natural language phonemes. This developmental disability is now known as left posterior superior temporal gyrus hypoplasia (Lpstgh), or, more commonly, as "Speech Processing Center Hypoplasia" ("SPCH"). See: Shibata, D.K. (2007) "Differences in Brain Structure in [Early] Deaf Persons on MR Imaging Studies with Voxel-Based Morphometry." American Journal of Neuroradiology, 28:243-249, February 2007 . [NOTE: RESEARCHERS AND SCHOLARS ARE CAUTIONED NOT TO ATTEND TO ANY PREVIOUS "RESEARCH" PRIOR TO THIS DATE OF FEBRUARY, 2007 OR ANY PERSONS DESIGNATING THEMSELVES AS "EXPERTS" ON THIS TOPIC WHO DO NOT QUOTE THIS ARTICLE OR THE OTHER SUBSEQUENT RESEARCH SUPPORTING THIS ARTICLE'S CONCLUSIONS AND FINDINGS].
The SPCH-deaf (early deafened) individuals do have normal vocal functions and can learn to speak. With the advent of the modern cochlear implant technologies, and if these are utilized immediately after deafness has been diagnosed (which can now be done right after birth), and with the total immersion of the individual with the cochlear implant into a completely auditory-verbal program of education, both at home and at school, the Lpstgh developmental disability and resulting speech disability can be remediated to a large extent. Such individuals are able to build a substantially normal structure in their left brain, and thus are able to produce very clear and understandable speech. Such individuals are commonly educated in Oral Schools for deaf and hard of hearing students -- See http://www.oraldeafed.org .
Others have families that utilize the Cued Speech (one-handed gestures to visually supplement the lipreading (speechreading) of phonetic sounds of natural languages -- See http://www.cuedspeech.org .
Others utilize Signed English or "Pidgin" Signed English, which uses the "sign" gestures to back-channel code the information being lipread, but this is visual-pictorial, not phonemic, and is often utilized when the individual has been through a program of oral-aural-vibrotactile training and when the person has already learned the phonemic sounds of human speech through these alternative methods. This is known properly as "Signed (Natural) Language," since the individual is thinking in the phonemic sounds of human speech, and has made the phonocentric shift to left-brain primary thought -- which can easily be determined by asking the individual to write in phonemic language. This is quite effective, since there is no spoken or written form of the non-phonemic gestural form of communication known as "(native) sign language ."
Persons with normal hearing ability, including adults, are able to learn and use the form of non-English, non-phonetic purely gestural communication known as "American Sign Language" in the USA, and as "natural sign languages" in other areas of the world. These normally take the form of copying the standard gestures used by persons with normal hearing in various societies, groups, and the shared created gestures utilized by the SPCH-deaf who did not have the opportunity to obtain and use cochlear implant technologies between birth to age 3, with full auditory-verbal immersive education.
A more minor, but still significant, form of Lpstgh is caused to the children with normal hearing ability whose parents, particularly the mothers, are part of the "silent, signing, nonspeaking" Lpstgh community (i.e. Edward Miner Gallaudet). This problem does not usually occur to the children with normal hearing whose parents, especially the mothers, are part of the "Oral-Aural" early-deafened community who were and still are trained in Oral Schools for deaf and hard of hearing students (i.e. Alexander Graham Bell).
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 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.