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.
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. One common metric used is the Levenshtein distance.
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For individuals to achieve moderate proficiency or understanding in a language (called L2) other than their first language (L1) typically requires considerable time and effort through study and/or practical application. 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 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.
Mutually intelligible languages or varieties of one languageEdit
There is no formal distinction between two distinct languages and two varieties of a single language, but some linguists use mutual intelligibility as one of the primary factors in deciding between the two cases.
Some linguists claim that mutual intelligibility is, ideally at least, the primary criterion separating languages from dialects. On the other hand, speakers of closely related languages can often communicate with each other; thus there are varying degrees of mutual intelligibility, and often other criteria are also used. 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, but speakers at one end cannot understand the speakers at the other end, the entire chain is often considered a single language. If the central varieties then 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.
In addition, political and social conventions often override considerations of mutual intelligibility. 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. 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.
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 some speakers cannot understand each other without recourse to a standard or prestige form.
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 not vice versa. For example, Dutch speakers tend to find it easier to understand Afrikaans than vice versa as a result of Afrikaans's simplified grammar, although the large number of false friends between these languages can cause misunderstanding.
Perhaps the most common reason for apparent asymmetric intelligibility is that speakers of one variety have more exposure to the other than vice versa. For example, speakers of Scottish English have frequent exposure to standard American English through movies and TV programs, whereas speakers of American English have little exposure to Scottish English; hence, American English speakers often find it difficult to understand Scottish English or, especially, Scots (which differs significantly from standard Scottish English), whereas Scots tend to have few problems understanding standard American English.
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 (see Mutual intelligibility in North Germanic languages). While Norway was under Danish rule, the Bokmål written standard of Norwegian originates from Dano-Norwegian, a koiné 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.
Similarly, in Germany and Italy, standard German or Italian speakers may have great difficulty understanding the "dialects" from regions other than their own, but virtually all "dialect" speakers learn the standard languages in school and from the media.
List of mutually intelligible languagesEdit
Below is an incomplete list of fully and partially mutually intelligible varieties sometimes considered languages.
Written and spoken formsEdit
- Afrikaans: Dutch (partially)
- Assyrian Neo-Aramaic: Turoyo (to a limited degree, asymmetrically)
- Astur-Leonese: Spanish, Galician and Portuguese (high)
- Azerbaijani: Crimean Tatar, Gagauz, Turkish and Urum (partially and asymmetrically[verification needed])
- Belarusian: Russian (partially) and Ukrainian (partially)
- Bulgarian: Macedonian
- Catalan: Occitan (high), Italian, Spanish and Portuguese (partially)
- Cebuano: Hiligaynon (high)
- Crimean Tatar: Azerbaijani, Gagauz, Turkish and Urum (partially and asymmetrically[verification needed])
- Corsican: Italian (high) and Sardinian (partially) 
- Czech: Slovak (significantly)
- Danish: Norwegian and Swedish (both partially and asymmetrically)
- Dutch: Afrikaans (in written form; in spoken form partially), Limburgish and West Frisian (partially)
- English: Scots (significantly)
- Estonian: Finnish (partially)
- Finnish: Estonian (partially), Karelian (high) Kven language and Meänkieli (very high)
- French: Walloon (high)
- Gagauz: Azerbaijani, Crimean Tatar, Turkish and Urum (partially and asymmetrically[verification needed])
- Galician: Astur-Leonese and Spanish (high), Portuguese (very high) 
- German: Luxembourgish (partially)
- Judaeo-Spanish: Spanish (high)
- Hiligaynon: Capiznon (very high) and Cebuano (high)
- Irish: Scottish Gaelic (partially; varies greatly according to dialect. The greatest mutual intelligibility is between Ulster Irish and southern Scottish dialects.). See also: Comparison of Scottish Gaelic and Irish.
- Italian: Corsican, Sicilian and Neapolitan (high), Catalan, Spanish, Sardinian and Portuguese (partially)
- Limburgish: Dutch and Afrikaans (partially) 
- Luxembourgish: German (partially)
- Macedonian: Bulgarian, Serbo-Croatian (partially and asymmetrically)
- Maltese: Tunisian Arabic (significantly) and Sicilian (partially)
- Manchu: Xibe
- Norwegian: Danish and Swedish (partially and asymmetrically)
- Portuguese: Galician (very high), Astur-Leonese (high), Spanish (high in written form; asymmetrically in spoken form), Catalan and Italian (partially)
- Occitan: Catalan (high), Franco-Provençal, Piedmontese and Ligurian (partially) 
- Russian: Belarusian and Ukrainian (both partially)
- Slovak: Czech (significantly) Polish (partially)
- Slovenian: Serbo-Croatian (partially and asymmetrically)
- Serbo-Croatian: Slovenian (partially and asymmetrically) Macedonian (partially and asymmetrically)
- Sardinian: Corsican and Italian (both partially), Spanish (partially)
- Spanish: Astur-Leonese and Galician (high), Portuguese (high in written form; asymmetrically in spoken form), Catalan and Italian (partially)
- Swedish: Danish and Norwegian (both partially and asymmetrically)
- Tunisian Arabic: Maltese (significantly), Algerian Arabic and Libyan Arabic (both partially)
- Moroccan Arabic: Algerian Arabic (high), yet the mutual intelligibility degree may vary depending on local dialects
- Turkish: Azerbaijani, Crimean Tatar, Gagauz and Urum (partially and asymmetrically[verification needed])
- Ukrainian: Belarusian and Russian (both partially)
- Urum: Azerbaijani, Crimean Tatar, Gagauz and Turkish (partially and asymmetrically[verification needed])
- Xibe: Manchu
- Zulu: Northern Ndebele (partially), Xhosa (partially), and Swazi (partially; the first three are often considered to be dialects of a uniform Zunda language)
Spoken forms mainlyEdit
- Akha, Honi, Hani (variety of different written scripts)
- Assyrian Neo-Aramaic: Lishanid Noshan (partially) and Hulaulá (partially) (because Assyrian Neo-Aramaic is usually written in the Syriac alphabet and the latter two are usually written in the Hebrew alphabet)
- Dari: Tajik (because, currently, Tajik is usually written using Cyrillic script, while Dari is usually written in the Persian alphabet).
- Dungan: Mandarin, especially with Central Plains Mandarin (partially; Dungan is usually written in Cyrillic and Mandarin usually in Chinese characters)
- German: Yiddish (because German is usually written in Latin script and Yiddish usually in the Hebrew alphabet). However, Yiddish's 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.
- Isan: Lao (because Isan is usually written in the Thai alphabet while Lao is usually written in the Lao alphabet, although Isan is a set of Lao dialects)
- Lao: Thai, Southern Thai, Lanna, Shan and Lü (both partially and asymmetrically, with every language having its own script while Thai and Southern Thai use the same script.)
- Persian: Tajik (because, currently, Persian is usually written in the Persian alphabet, but Tajik is usually written using the Cyrillic script)
- Polish: Ukrainian and Belarusian (both partially, because Belarusian and Ukrainian are written in Cyrillic, while Polish is written in Latin)
- Tajik: Persian and Dari (because, currently, Tajik is usually written in Cyrillic, whereas Persian and Dari are usually written in the Persian alphabet)
Written forms mainlyEdit
- Icelandic: Faroese
- French: With some Romance languages.
- German: Dutch. Standard Dutch and Standard German show a limited degree of mutual intelligibility when written. One study concluded that when concerning written language, Dutch speakers could translate 50.2% of the provided German words correctly, while the German test subjects were able to translate 41.9% of the Dutch equivalents correctly. In terms of orthography, 22% of the vocabulary of Dutch and German is identical or near identical (including most commonly used vocabulary). The Levenshtein distance between written Dutch and German is 50.4% as opposed to 61.7% between English and Dutch. The spoken languages are much more difficult to understand for both, with studies showing Dutch speakers having slightly less difficulty in understanding German speakers than vice versa, though it remains unclear whether this asymmetry has to do with prior knowledge of the language (Dutch people being more exposed to German than vice versa), better knowledge of another related language (English) or any other non-linguistic reasons.
List of mutually intelligible varietiesEdit
- Dari: Persian
- Karakalpak: Kazakh and Nogai
- Kazakh: Karakalpak, Nogai, Altay and Kyrgyz
- Kinyarwanda: Kirundi
- Kirundi: Kinyarwanda
- Kyrgyz: Kazakh and Altay and Karakalpak
- Persian: Dari
- Samoan: Tokelauan and Tuvaluan (partially)
- Tokelauan: Tuvaluan and Samoan (partially)
- Tuvaluan: Tokelauan and Samoan (partially)
Dialects or registers of one language sometimes considered separate languagesEdit
- Assyrian Neo-Aramaic: Chaldean Neo-Aramaic, Lishana Deni, Hértevin, Bohtan Neo-Aramaic, and Senaya – the standard forms are structurally the same language and thus mutually intelligible to a significant degree. As such, these varieties are occasionally considered dialects of Assyrian Neo-Aramaic. They are only considered separate languages for geographical, political and religious reasons.
- Catalan: Valencian – the standard forms are structurally the same language, and hence 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 vocabulary mainly from Sanskrit and Urdu drawing it mainly from Persian and Arabic.
- Malay: Indonesian (the normative register regulated by Indonesia) and Standard Malay/Malaysian (the normative register used in Malaysia, Brunei and Singapore). Both varieties are based on the same material basis and hence are generally mutually intelligible, despite the numerous lexical differences.
- Serbo-Croatian: Bosnian, Croatian, Montenegrin, and Serbian – the national varieties are structurally the same language, all constituting normative registers 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.
- The non-standard vernacular dialects of Serbo-Croatian (Kajkavian, Chakavian and Torlakian) are considered by some linguists to be separate, albeit closely related languages to Serbo-Croatian (Shtokavian), rather than its dialects, as Shotkavian has its own set of subdialects. Their mutual intelligibility varies greatly, both between the dialects themselves as well as with other languages. Kajkavian has higher mutual intelligibility with Slovenian than the national varieties of Shtokavian, while Chakavian has a low mutual intelligibility with either, in part due to large number of loanwords from Venetian. Torlakian (considered a subdialect of Serbian Old Shtokavian by some) has a significant level of 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.
- Tagalog: Filipino – the national language of the Philippines, Filipino, is based almost entirely on the Luzon dialects of Tagalog
- 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 intelligiblity.
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, Spanish, Aragonese, Catalan;
- Occitano-Romance: Catalan, Occitan;
- Gallo-Romance: Langues d'oïl (including French), Franco-Provençal;
- Rhaeto-Romance: Romansh, Ladin, Friulian;
- Gallo-Italic: Piedmontese, Ligurian, Lombard, Emilian-Romagnol;
- Italo-Dalmatian: Corsican, Dalmatian (extinct), Italian, Neapolitan, Sicilian;
- Eastern Romance: Daco-Romanian, Istro-Romanian, Aromanian, Megleno-Romanian.
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