Mutual intelligibility

In linguistics, mutual intelligibility is a relationship between languages or dialects in which speakers of different but related varieties can readily understand each other without prior familiarity or special effort. It is sometimes used as an important criterion for distinguishing languages from dialects, although sociolinguistic factors are often also used.

Intelligibility between languages can be asymmetric, with speakers of one understanding more of the other than speakers of the other understanding the first. When it is relatively symmetric, it is characterized as "mutual". It exists in differing degrees among many related or geographically proximate languages of the world, often in the context of a dialect continuum.

Factors
An individual's achievement of moderate proficiency or understanding in a language (called L2) other than their first language (L1) typically requires considerable time and effort through study and practical application if the two languages are not very closely related. Advanced speakers of a second language typically aim for intelligibility, especially in situations where they work in their second language and the necessity of being understood is high. However, many groups of languages are partly mutually intelligible, i.e. most speakers of one language find it relatively easy to achieve some degree of understanding in the related language(s). Often the two languages are genetically related, and they are likely to be similar to each other in grammar, vocabulary, pronunciation, or other features.

Intelligibility among languages can vary between individuals or groups within a language population according to their knowledge of various registers and vocabulary in their own language, their exposure to additional related languages, their interest in or familiarity with other cultures, the domain of discussion, psycho-cognitive traits, the mode of language used (written vs. oral), and other factors.

Linguistic distance is the name for the concept of calculating a measurement for how different languages are from one another. The higher the linguistic distance, the lower the mutual intelligibility.

Asymmetric intelligibility
Asymmetric intelligibility refers to two languages that are considered partially mutually intelligible, but where one group of speakers has more difficulty understanding the other language than the other way around. There can be various reasons for this. If, for example, one language is related to another but has simplified its grammar, the speakers of the original language may understand the simplified language, but less vice versa. For example, Dutch speakers tend to find it easier to understand Afrikaans than vice versa as a result of Afrikaans' simplified grammar.

Among sign languages
Sign languages are not universal and are usually not mutually intelligible, although there are also similarities among different sign languages. Sign languages are independent of spoken languages and follow their own paths of development. For example, British Sign Language (BSL) and American Sign Language (ASL) are quite different and mutually unintelligible, even though the hearing people of the United Kingdom and the United States share the same spoken language. The grammars of sign languages do not usually resemble those of spoken languages used in the same geographical area; in fact, in terms of syntax, ASL shares more with spoken Japanese than it does with English.

As a criterion for identifying separate languages
Some linguists use mutual intelligibility as a primary criterion for determining whether two speech varieties represent the same or different languages. In a similar vein, some claim that mutual intelligibility is, ideally at least, the primary criterion separating languages from dialects.

A primary challenge to these positions is that speakers of closely related languages can often communicate with each other effectively if they choose to do so. In the case of transparently cognate languages officially recognized as distinct such as Spanish and Italian, mutual intelligibility is in principle and in practice not binary (simply yes or no), but occurs in varying degrees, subject to numerous variables specific to individual speakers in the context of the communication. Classifications may also shift for reasons external to the languages themselves. As an example, in the case of a linear dialect continuum that shades gradually between varieties, where speakers near the center can understand the varieties at both ends with relative ease, but speakers at one end have difficulty understanding the speakers at the other end, the entire chain is often considered a single language. If the central varieties die out and only the varieties at both ends survive, they may then be reclassified as two languages, even though no actual language change has occurred during the time of the loss of the central varieties. In this case, too, however, while mutual intelligibility between speakers of the distant remnant languages may be greatly constrained, it is likely not at the zero level of completely unrelated languages.

In addition, political and social conventions often override considerations of mutual intelligibility in both scientific and non-scientific views. For example, the varieties of Chinese are often considered a single language even though there is usually no mutual intelligibility between geographically separated varieties. Another similar example would be varieties of Arabic, which additionally share a single prestige variety in Modern Standard Arabic. In contrast, there is often significant intelligibility between different Scandinavian languages, but as each of them has its own standard form, they are classified as separate languages.

However, others have suggested that these objections are misguided, as they collapse different concepts of what constitutes a "language".

To deal with the conflict in cases such as Arabic, Chinese and German, the term Dachsprache (a sociolinguistic "umbrella language") is sometimes seen: Chinese and German are languages in the sociolinguistic sense even though speakers of some varieties cannot understand each other without recourse to a standard or prestige form.

North Germanic
Northern Germanic languages spoken in Scandinavia form a dialect continuum where two furthermost dialects have almost no mutual intelligibility. As such, spoken Danish and Swedish normally have low mutual intelligibility, but Swedes in the Öresund region (including Malmö and Helsingborg), across a strait from the Danish capital Copenhagen, understand Danish somewhat better, largely due to the proximity of the region to Danish-speaking areas. While Norway was under Danish rule, the Bokmål written standard of Norwegian developed from Dano-Norwegian, a koiné language that evolved among the urban elite in Norwegian cities during the later years of the union. Additionally, Norwegian assimilated a considerable amount of Danish vocabulary as well as traditional Danish expressions. As a consequence, spoken mutual intelligibility is not reciprocal.

Romance
Because of the difficulty of imposing boundaries on a continuum, various counts of the Romance languages are given; in The Linguasphere register of the world's languages and speech communities David Dalby lists 23 based on mutual intelligibility:
 * Iberian Romance: Portuguese, Galician, Mirandese, Astur-Leonese, Castilian, Aragonese;
 * Occitano-Romance: Catalan, Occitan, Sardinian;
 * Gallo-Romance: Langues d'oïl (including French), Piedmontese, Franco-Provençal;
 * Rhaeto-Romance: Romansh, Ladin, Friulian;
 * Gallo-Italic: Piedmontese, Ligurian, Lombard, Emilian-Romagnol, Venetian;
 * Italo-Dalmatian (including Italian): Corsican, Neapolitan, Sicilian, Istriot, Dalmatian (extinct);
 * Eastern Romance: Daco-Romanian, Istro-Romanian, Aromanian, Megleno-Romanian.

South Slavic
Serbo-Croatian dialects in relation to Slovene, Macedonian, and Bulgarian: The non-standard vernacular dialects of Serbo-Croatian (i.e. non-Shtokavian dialects: Kajkavian, Chakavian and Torlakian) diverge more significantly from all four normative varieties. Their mutual intelligibility varies greatly, between the dialects themselves, with Shtokavian, and with other languages. For example, Torlakian which is considered a subdialect of Serbian Old Shtokavian by some, has significant mutual intelligibility with Macedonian and Bulgarian. All South Slavic languages in effect form a large dialect continuum of gradually mutually intelligible varieties depending on distance between the areas where they are spoken.

Romance

 * Italian and French (moderately)
 * Italian and Spanish (partially)
 * Portuguese and Galician (significantly)
 * Portuguese and Italian (moderately)
 * Romanian, Aromanian, Megleno-Romanian and Istro-Romanian (significantly)
 * Spanish and Portuguese (moderately)
 * Spanish and Judaeo-Spanish (spoken or written in the Latin alphabet; Judaeo-Spanish may also be written in the Hebrew alphabet). Depending on dialect and the number of non-Spanish loanwords used.

Germanic

 * Danish, Norwegian and Swedish (partially and asymmetrically)
 * Dutch and Afrikaans (in written form; in spoken form partially)
 * Dutch and West Frisian (partially)
 * English and Scots (partially)
 * German and Yiddish (only spoken, because German is usually written in Latin script and Yiddish usually in the Hebrew alphabet). However, Yiddish use of many borrowed words, chiefly from Hebrew and Slavic languages, makes it more difficult for a German speaker to understand spoken Yiddish than the reverse.

Slavic

 * Belarusian, Russian and Ukrainian (partially)
 * Bulgarian and Macedonian (significantly)
 * Czech and Slovak (significantly)
 * Czech and Polish (partially and asymmetrically)
 * Macedonian and Serbo-Croatian (moderately to significantly)
 * Polish and Slovak (reasonably to partially)
 * Polish, Ukrainian and Belarusian (both partially; moreover, Belarusian and Ukrainian are written in Cyrillic, while Polish is written in Latin)
 * Serbo-Croatian and Slovene (moderately)

Indo-Aryan

 * Bengali, Assamese as well as Odia. Please refer to the respective pages for more information.
 * Chittagonian and Rohingya (The Chittagonian and Rohingya languages have a high degree of mutual intelligibility, while Chittagonian is written with Bengali script and Rohingya is written with Hanifi script)
 * Hindi and Urdu. See the article on Hindustani language.
 * Marathi and certain dialects of Konkani (significantly)

Turkic

 * Azerbaijani, Crimean Tatar, Gagauz, Turkish and Urum  (partially and asymmetrically)
 * Uzbek and Uyghur (formerly known as Western and Eastern dialects of Turki; Uzbek uses a Latin alphabet whereas Uyghur uses an alphabet based on the Arabic script)
 * Karakalpak, Kazakh, Kyrgyz and Nogai. Many Turkic languages are mutually intelligible to a higher or lower degree, but thorough empirical research is needed to establish the exact levels and patterns of mutual intelligibility between the languages of this linguistic family. The British Academy funded research project dedicated to examining mutual intelligibility between Karakalpak, Kazakh and Uzbek languages is currently under way at the University of Surrey.

Austronesian

 * Hiligaynon, Capiznon (significantly) and Cebuano (significantly)
 * Iban and Malay, especially with Sarawakian Malay (partially)
 * Tokelauan and Tuvaluan

Niger–Congo

 * Esan and Edo (the different varieties of Edoid languages are mutually intelligible, such that successful communication between speakers is not affected).
 * Kinyarwanda and Kirundi
 * Zulu, Northern Ndebele (partially), Xhosa (partially), and Swazi (partially)
 * Luganda and Lusoga (partially)
 * Nkore and Kiga

Other

 * Akha, Honi and Hani (variety of different written scripts)
 * Dungan and Mandarin, especially with Central Plains Mandarin (partially; Dungan is usually written in Cyrillic and Mandarin usually in Chinese characters)
 * Estonian and Finnish (partially)
 * Finnish and Karelian (significantly)
 * Irish and Scottish Gaelic (partially)
 * Manchu and Xibe
 * Thai, Southern Thai, Lao (Isan), Northern Thai, Shan and Tai Lue (both partially and asymmetrically; only Central Thai and Southern Thai are significantly mutually intelligible both in written and spoken forms, while other languages have their own scripts.)
 * Tunisian Arabic and Maltese (32–33% of sentences; Maltese is written with the Latin script while Tunisian Arabic is written with the Arabic script)
 * Tunisian Arabic and Libyan Arabic (68–70% of sentences)

List of dialects or varieties sometimes considered separate languages

 * Akan: Twi and Fante.
 * Northeastern Neo-Aramaic (NENA) is a dialect continuum, with some dialects being mutually intelligible and others not. While Zakho Jewish Neo-Aramaic and Zakho Christian Neo-Aramaic are mutually intelligible, especially on the eastern edge (in Iran), Jewish and Christian NENA varieties spoken in the same town are not mutually intelligible.
 * Catalan: Valencian – the standard forms are structurally the same language and share the vast majority of their vocabulary, and hence highly mutually intelligible. They are considered separate languages only for political reasons.
 * Hindustani: Hindi and Urdu – the standard forms are separate registers of structurally the same language (called Hindustani or Hindi-Urdu), with Hindi written in Devanagari and Urdu mainly in a Perso-Arabic script, and with Hindi drawing its literary and formal vocabulary mainly from Sanskrit and Urdu drawing it mainly from Persian and Arabic.
 * Malay: Indonesian (the standard regulated by Indonesia), Brunei and Malaysian (the standard used in Malaysia and Singapore). Both varieties are based on the same material basis and hence are generally mutually intelligible, despite the numerous lexical differences. Certain linguistic sources also treat the two standards on equal standing as varieties of the same Malay language. Malaysians tend to assert that Malaysian and Indonesian are merely different normative varieties of the same language, while Indonesians tend to treat them as separate, albeit closely related, languages. However, vernacular or less formal varieties spoken between these two countries share limited intelligibility, evidenced by Malaysians having difficulties understanding Indonesian sinetron (soap opera) aired on their TV stations (which actually uses a colloquial offshoot heavily influenced by Betawi vernacular of Jakarta rather than the formal standard acquired in academical contexts) and vice versa.
 * Persian: Iranian Persian (natively simply known as Persian), Dari and Tajik – Persian and Dari are written in Perso-Arabic script, while Tajik is written in Cyrillic script.
 * Serbo-Croatian: Bosnian, Croatian, Montenegrin, and Serbian – the national varieties are structurally the same language, all constituting normative varieties of the Shtokavian dialect, and hence mutually intelligible, spoken and written (if the Latin alphabet is used). For political reasons, they are sometimes considered distinct languages. Shtokavian has its own set of subdialects, leading some linguists to consider the other dialects (Kajkavian, Chakavian, and Torlakian) as separate languages, closely related to Shtokavian Serbo-Croatian (rather than being Serbo-Croatian dialects).
 * Romanian: Moldovan – the standard forms are structurally the same language, and hence mutually intelligible. They are considered separate languages only for political reasons. Moldovan does, however, have more foreign loanwords from Russian and Ukrainian due to historical East Slavic influence on the region but not to the extent where those would affect mutual intelligibility. A law declaring Romanian as the official language of Moldova was passed by the Moldovan parliament in 2023, after that only pro-Russian separatist region of Transnistria still describes its language as Moldovan rather than Romanian (and cyrillic alphabet is used there instead of the Latin one).
 * Tagalog: Filipino – the national language of the Philippines, Filipino, is based almost entirely on the Luzon dialects of Tagalog.