The term dialect (from Latin dialectus, dialectos, from the Ancient Greek word διάλεκτος, diálektos, "discourse", from διά, diá, "through" and λέγω, légō, "I speak") is used in two distinct ways to refer to two different types of linguistic phenomena:

A dialect is distinguished by its vocabulary, grammar, and pronunciation (phonology, including prosody). Where a distinction can be made only in terms of pronunciation (including prosody, or just prosody itself), the term accent may be preferred over dialect. Other types of speech varieties include jargons, which are characterized by differences in lexicon (vocabulary); slang; patois; pidgins; and argots. The particular speech patterns used by an individual are termed an idiolect.

A standard dialect (also known as a "standardized dialect" or "standard language") is a dialect that is supported by institutions. Such institutional support may include government recognition or designation; presentation as being the "correct" form of a language in schools; published grammars, dictionaries, and textbooks that set forth a normative spoken and written form; and an extensive formal literature that employs that variety (prose, poetry, non-fiction, etc.). There may be multiple standard dialects associated with a single language. For example, Standard American English, Standard British English, Standard Canadian English, Standard Indian English, Standard Australian English, and Standard Philippine English may all be said to be standard dialects of the English language.

A nonstandard dialect, like a standard dialect, has a complete grammar and vocabulary, but is usually not the beneficiary of institutional support. Examples of a nonstandard English dialect are Southern American English, Western Australian English, New York English, New England English, Mid-Atlantic American or Philadelphia / Baltimore English, Scouse, Brummie, Cockney, and Tyke. The Dialect Test was designed by Joseph Wright to compare different English dialects with each other.

There is no universally accepted criterion for distinguishing two different languages from two dialects (i.e. varieties) of the same language.^[21] A number of rough measures exist, sometimes leading to contradictory results.

The western in its origins distinction (dichotomy) between dialect and language is therefore subjective (arbitrary) and depends upon the user's preferred frame of reference.^[22] For example, there has been discussion about whether or not the Limón Creole English should be considered "a kind" of English or a different language. This creole is spoken in the Caribbean coast of Costa Rica (Central America) by descendants of Jamaican people. The position that Costa Rican linguists support depends upon which University they represent.

One criterion, which is often considered to be purely linguistic, is that of mutual intelligibility: two varieties are said to be dialects of the same language if being a speaker of one variety confers sufficient knowledge to understand and be understood by a speaker of the other; otherwise, they are said to be different languages.^[23] However, this definition cannot consistently delimit languages in the case of a dialect continuum (or dialect chain), containing a sequence of varieties, each mutually intelligible with the next, but where widely separated varieties may not be mutually intelligible.^[23] Further problems with this criterion are that mutual intelligibility occurs in varying degrees, and that it is difficult to distinguish from prior familiarity with the other variety.

Reported mutual intelligibility may also be affected by speakers' attitudes to the other speech community.^[24]

Another occasionally used criterion for discriminating dialects from languages is the sociolinguistic notion of linguistic authority. According to this definition, two varieties are considered dialects of the same language if (under at least some circumstances) they would defer to the same authority regarding some questions about their language. For instance, to learn the name of a new invention, or an obscure foreign species of plant, speakers of Westphalian and East Franconian German might each consult a German dictionary or ask a German-speaking expert in the subject. Thus these varieties are said to be dependent on, or heteronomous with respect to, Standard German, which is said to be autonomous.^[25] In contrast, speakers in the Netherlands of Low Saxon varieties similar to Westphalian would instead consult a dictionary of Standard Dutch. Similarly, although Yiddish is classified by linguists as a language in the Middle High German group of languages, a Yiddish speaker would consult a different dictionary in such a case.

Within this framework, W. A. Stewart defined a language as an autonomous variety together with all the varieties that are heteronomous with respect to it, noting that an essentially equivalent definition had been stated by Charles A. Ferguson and John J. Gumperz in 1960.^[26][27] Similarly, a heteronomous variety may be considered a dialect of a language defined in this way.^[26] In these terms, Danish and Norwegian, though mutually intelligible to a large degree, are considered separate languages.^[28] In the framework of Heinz Kloss, these are described as languages by ausbau (development) rather than by abstand (separation).^[29]

In other situations, a closely related group of varieties possess considerable (though incomplete) mutual intelligibility, but none dominates the others.

To describe this situation, the editors of the Handbook of African Languages introduced the term dialect cluster as a classificatory unit at the same level as a language.^[30] A similar situation, but with a greater degree of mutual unintelligibility, has been termed a language cluster.^[31]

In many societies, however, a particular dialect, often the sociolect of the elite class, comes to be identified as the "standard" or "proper" version of a language by those seeking to make a social distinction and is contrasted with other varieties. As a result of this, in some contexts, the term "dialect" refers specifically to varieties with low social status. In this secondary sense of "dialect", language varieties are often called dialects rather than languages:

The status of "language" is not solely determined by linguistic criteria, but it is also the result of a historical and political development.

Romansh came to be a written language, and therefore it is recognized as a language, even though it is very close to the Lombardic alpine dialects. An opposite example is the case of Chinese, whose variations such as Mandarin and Cantonese are often called dialects and not languages in China, despite their mutual unintelligibility.

Modern nationalism, as developed especially since the French Revolution, has made the distinction between "language" and "dialect" an issue of great political importance. A group speaking a separate "language" is often seen as having a greater claim to being a separate "people", and thus to be more deserving of its own independent state, while a group speaking a "dialect" tends to be seen not as "a people" in its own right, but as a sub-group, part of a bigger people, which must content itself with regional autonomy. The distinction between language and dialect is thus inevitably made at least as much on a political basis as on a linguistic one, and can lead to great political controversy or even armed conflict.

The Yiddish linguist Max Weinreich published the expression, A shprakh iz a dialekt mit an armey un flot ("אַ שפּראַך איז אַ דיאַלעקט מיט אַן אַרמײ און פֿלאָט"‎: "A language is a dialect with an army and navy") in YIVO Bleter 25.1, 1945, p. 13. The significance of the political factors in any attempt at answering the question "what is a language?" is great enough to cast doubt on whether any strictly linguistic definition, without a socio-cultural approach, is possible. This is illustrated by the frequency with which the army-navy aphorism is cited.

By the definition most commonly used by linguists, any linguistic variety can be considered a "dialect" of some language—"everybody speaks a dialect". According to that interpretation, the criteria above merely serve to distinguish whether two varieties are dialects of the same language or dialects of different languages.

The terms "language" and "dialect" are not necessarily mutually exclusive, although it is often perceived to be.

Thus there is nothing contradictory in the statement "the language of the Pennsylvania Dutch is a dialect of German".

There are various terms that linguists may use to avoid taking a position on whether the speech of a community is an independent language in its own right or a dialect of another language.

Perhaps the most common is "variety";^[32] "lect" is another. A more general term is "languoid", which does not distinguish between dialects, languages, and groups of languages, whether genealogically related or not.^[33]

John Lyons writes that "Many linguists [...] subsume differences of accent under differences of dialect."^[8] In general, accent refers to variations in pronunciation, while dialect also encompasses specific variations in grammar and vocabulary.^[34]

When talking about the German language, the term German dialects is only used for the traditional regional varieties. That allows them to be distinguished from the regional varieties of modern standard German.

The German dialects show a wide spectrum of variation.

Some of them are not mutually intelligible.

German dialectology traditionally names the major dialect groups after Germanic tribes from which they were assumed to have descended.^[35]

The extent to which the dialects are spoken varies according to a number of factors: In Northern Germany, dialects are less common than in the South.

In cities, dialects are less common than in the countryside.

In a public environment, dialects are less common than in a familiar environment.

The situation in Switzerland and Liechtenstein is different from the rest of the German-speaking countries. The Swiss German dialects are the default everyday language in virtually every situation, whereas standard German is only spoken in education, partially in media, and with foreigners not possessing knowledge of Swiss German. Most Swiss German speakers perceive standard German to be a foreign language.

The Low German varieties spoken in Germany are often counted among the German dialects. This reflects the modern situation where they are roofed by standard German. This is different from the situation in the Middle Ages when Low German had strong tendencies towards an ausbau language.

The Frisian languages spoken in Germany are excluded from the German dialects.

Italy is an often quoted example of a country where the second definition of the word "dialect" (dialetto) is most prevalent. Italy is in fact home to a vast array of languages, most of which are Latin-based, lack mutual intelligibility with one another, and have their own local varieties; twelve of them (Albanian, Catalan, German, Greek, Slovene, Croatian, French, Franco-Provençal, Friulian, Ladin, Occitan and Sardinian) underwent some Italianization but are officially recognized as minority languages (minoranze linguistiche storiche) nowadays, in light of their distinctive historical development. Yet, most of the regional languages spoken across the peninsula are often colloquially referred to in non-linguistic circles as Italian dialetti, since even the prestigious Neapolitan, Sicilian and Venetian have had the Tuscan-based standard Italian as their reference language since the Middle Ages. However, only a few of them are actually derived from modern standard Italian, the majority being rather evolved from Vulgar Latin separately and individually from one another and independently of standard Italian, long prior to the popular diffusion of the latter throughout what is now Italy.^[36]

The most widely spoken languages of Italy fall within a family of which even standard Italian is part, the Italo-Dalmatian group. This wide category includes:

Modern standard Italian is heavily based on the Florentine dialect of Tuscan.^[36] The Tuscan-based language that would eventually become modern standard Italian had been used in poetry and literature since at least the 12th century, and it first spread throughout Italy among the educated upper class through the works of the so-called tre corone ("three crowns"): Dante Alighieri, Petrarch, and Giovanni Boccaccio. Florentine thus gradually rose to prominence as the volgare (colloquial speech) of the literate and upper class in Italy, and it spread throughout the peninsula and Sicily as the lingua franca among the Italian educated class as well as Italian traveling merchants. The economic prowess and cultural and artistic importance of Tuscany in the Late Middle Ages and the Renaissance further encouraged the diffusion of the Florentine-Tuscan Italian throughout Italy and among the educated and powerful, though local and regional languages remained the main languages of the common people.

Aside from the Italo-Dalmatian languages, the second most widespread family in Italy is the Gallo-Italic group, spanning throghout much of Northern Italy's languages and dialects (such as Piedmontese, Emilian-Romagnol, Ligurian, Lombard, Venetian, Sicily's and Basilicata's Gallo-Italic in southern Italy, etc.).

Finally, other languages from a number of different families follow the last two major groups: the Gallo-Romance languages (French, Occitan and its Vivaro-Alpine dialect, Franco-Provençal); the Rhaeto-Romance languages (Friulian and Ladin); the Ibero-Romance languages (Sardinia's Algherese); the Germanic Cimbrian, Southern Bavarian, Walser German and the Mòcheno language; the Albanian Arbëresh language; the Hellenic Griko language and Calabrian Greek; the Serbo-Croatian Slavomolisano dialect; and the various Slovene languages, including the Gail Valley dialect and Istrian dialect. The language indigenous to Sardinia, while being Romance in nature, is considered to be a specific linguistic family of its own, separate from all the other Neo-Latin groups; it is often subdivided into the Centro-Southern and Centro-Northern dialects.

Though mostly mutually unintelligible, the exact degree to which all the Italian languages are mutually unintelligible varies, often correlating with geographical distance or geographical barriers between the languages; some regional Italian languages that are closer in geographical proximity to each other or closer to each other on the dialect continuum are more or less mutually intelligible. For instance, a speaker of purely Eastern Lombard, a language in Northern Italy's Lombardy region that includes the Bergamasque dialect, would have severely limited mutual intelligibility with a purely standard Italian speaker and would be nearly completely unintelligible to a Sicilian-speaking individual. Due to Eastern Lombard's status as a Gallo-Italic language, an Eastern Lombard speaker may, in fact, have more mutual intelligibility with an Occitan, Catalan, or French speaker than with a standard Italian or Sicilian speaker. Meanwhile, a Sicilian-speaking person would have a greater degree of mutual intelligibility with a speaker of the more closely related Neapolitan language, but far less mutual intelligibility with a person speaking Sicilian Gallo-Italic, a language that developed in isolated Lombard emigrant communities on the same island as the Sicilian language.

During the Risorgimento, proponents of Italian republicanism and Italian nationalism, like the Lombard Alessandro Manzoni, stressed the importance of establishing a uniform national language in order to better create an Italian national identity.^[37] With the unification of Italy in the 1860s, standard Italian became the official national language of the new Italian state, while the other ones became to be institutionally regarded as subordinate dialects to Italian, and negatively associated with lack of education or provincialism. However, at the time of the Italian Unification, standard Italian still existed mainly as a literary language, and only 2.5% of Italy's population could speak standard Italian.^[38]

In the early 20th century, the vast conscription of Italian men from all throughout Italy during World War I is credited with facilitating the diffusion of standard Italian among less educated Italian men, as these men from various regions with various regional languages were forced to communicate with each other in a common tongue while serving in the Italian military. With the popular spread of standard Italian out of the intellectual circles, because of the mass-media and the establishment of public education, Italians from all regions were increasingly exposed to standard Italian.^[36] While "dialect" levelling has increased the number of standard Italian speakers and decreased the number of speakers of other languages native to Italy, Italians in different regions have developed variations of standard Italian particular to their region. These variations on standard Italian, known as regional Italian, would thus more appropriately be called "dialects" in accordance with the first linguistic definition of "dialect", as they are in fact derived partially or mostly from standard Italian,^[39][16][40] with some degree of influence from the local or regional native languages and accents.^[36]

Today, the majority of Italians are able to speak standard Italian, though many Italians still speak their regional language regularly or as their primary day-to-day language, especially at home with family or when communicating with Italians from the same town or region.

The classification of speech varieties as dialects or languages and their relationship to other varieties of speech can be controversial and the verdicts inconsistent.

Serbo-Croatian illustrates this point. Serbo-Croatian has two major formal variants (Serbian and Croatian). Both are based on the Shtokavian dialect and therefore mutually intelligible with differences found mostly in their respective local vocabularies and minor grammatical differences. Certain dialects of Serbia (Torlakian) and Croatia (Kajkavian and Chakavian

Macedonian, although largely mutually intelligible with Bulgarian and certain dialects of Serbo-Croatian (Torlakian), is considered by Bulgarian linguists to be a Bulgarian dialect, in contrast with the contemporary international view and the view in North Macedonia, which regards it as a language in its own right. Nevertheless, before the establishment of a literary standard of Macedonian in 1944, in most sources in and out of Bulgaria before the Second World War, the southern Slavonic dialect continuum covering the area of today's North Macedonia were referred to as Bulgarian dialects.

In Lebanon, a part of the Christian population considers "Lebanese" to be in some sense a distinct language from Arabic and not merely a dialect. During the civil war Christians often used Lebanese Arabic officially, and sporadically used the Latin script to write Lebanese, thus further distinguishing it from Arabic. All Lebanese laws are written in the standard literary form of Arabic, though parliamentary debate may be conducted in Lebanese Arabic.

In Tunisia, Algeria, and Morocco, the Darijas (spoken North African languages) are sometimes considered more different from other Arabic dialects. Officially, North African countries prefer to give preference to the Literary Arabic and conduct much of their political and religious life in it (adherence to Islam), and refrain from declaring each country's specific variety to be a separate language, because Literary Arabic is the liturgical language of Islam and the language of the Islamic sacred book, the Qur'an. Although, especially since the 1960s, the Darijas are occupying an increasing use and influence in the cultural life of these countries. Examples of cultural elements where Darijas' use became dominant include: theatre, film, music, television, advertisement, social media, folk-tale books and companies' names.

The Modern Ukrainian language has been in common use since the late 17th century, associated with the establishment of the Cossack Hetmanate. In the 19th century, the Tsarist Government of the Russian Empire claimed that Ukrainian was merely a dialect of Russian and not a language on its own. According to these claims, the differences were few and caused by the conquest of western Ukraine by the Polish-Lithuanian Commonwealth. However, in reality the dialects in Ukraine were developing independently from the dialects in the modern Russia for several centuries, and as a result they differed substantially.

Following the signing of the Brest-Litovsk Treaty, the German Empire briefly gained control over Ukraine during World War I, but was eventually defeated by the Entente, with major involvement by the Ukrainian Bolsheviks. After Bolsheviks managed to conquer the rest of Ukraine from the Ukrainian People's Republic and the Whites, Ukraine became part of the USSR, whence a process of Ukrainization was begun, with encouragement from Moscow. However, in the late 1920s - early 1930s, the process started to reverse. Witnessing the Ukrainian cultural revival spurred by the Ukrainization in the early 1920s, and fearing that it might lead to an independence movement, Moscow started to remove from power and in some cases physically eliminate the public proponents of ukrainization. The appointment of Pavel Postyshev as the secretary of the Communist Party of Ukraine marked the end of ukrainization, and the opposite process of russification started. After World War II, citing Ukrainian collaboration with Nazi Germany in an attempt to gain independence as the reason, Moscow changed its policy towards repression of the Ukrainian language.

Today the boundaries of the Ukrainian language to the Russian language are still not drawn clearly, with an intermediate dialect between them, called Surzhyk, developing in Ukraine.

There have been cases of a variety of speech being deliberately reclassified to serve political purposes.

One example is Moldovan. In 1996, the Moldovan parliament, citing fears of "Romanian expansionism", rejected a proposal from President Mircea Snegur to change the name of the language to Romanian, and in 2003 a Moldovan–Romanian dictionary was published, purporting to show that the two countries speak different languages. Linguists of the Romanian Academy reacted by declaring that all the Moldovan words were also Romanian words; while in Moldova, the head of the Academy of Sciences of Moldova, Ion Bărbuţă, described the dictionary as a politically motivated "absurdity".

Unlike languages that use alphabets to indicate their pronunciation, Chinese characters have developed from logograms that do not always give hints to their pronunciation. Although the written characters have remained relatively consistent for the last two thousand years, the pronunciation and grammar in different regions have developed to an extent that the varieties of the spoken language are often mutually unintelligible. As a series of migration to the south throughout the history, the regional languages of the south, including Gan, Xiang, Wu, Min, Yue and Hakka often show traces of Old Chinese or Middle Chinese. From the Ming dynasty onward, Beijing has been the capital of China and the dialect spoken in Beijing has had the most prestige among other varieties. With the founding of the Republic of China, Standard Mandarin was designated as the official language, based on the spoken language of Beijing. Since then, other spoken varieties are regarded as fangyan (regional speech). Cantonese is still the most commonly-used language in Guangzhou, Hong Kong, Macau and among some overseas Chinese communities, whereas Hokkien has been accepted in Taiwan as an important local language alongside Mandarin.

One language, Interlingua, was developed so that the languages of Western civilization would act as its dialects.^[41] Drawing from such concepts as the international scientific vocabulary and Standard Average European, linguists developed a theory that the modern Western languages were actually dialects of a hidden or latent language. Researchers at the International Auxiliary Language Association extracted words and affixes that they considered to be part of Interlingua's vocabulary.^[42] In theory, speakers of the Western languages would understand written or spoken Interlingua immediately, without prior study, since their own languages were its dialects.^[41] This has often turned out to be true, especially, but not solely, for speakers of the Romance languages and educated speakers of English. Interlingua has also been found to assist in the learning of other languages. In one study, Swedish high school students learning Interlingua were able to translate passages from Spanish, Portuguese, and Italian that students of those languages found too difficult to understand.^[43]*International%20languages%3A%20A%20matter]]*International%20languages%3A%20A%20matter]]*he vocabulary of Interlingua extends beyond the Western language families.