Dozens of dialects are spoken in Japan. The profusion is due to many factors, including the length of time the archipelago has been inhabited, its mountainous island terrain, and Japan's long history of both external and internal isolation. Dialects typically differ in terms of pitch accent, inflectional morphology, vocabulary, and particle usage. Some even differ in vowel and consonant inventories, although this is uncommon.
The main distinction in Japanese dialects is between Tokyo-type (東京式, Tōkyō-shiki?) and Western-type (京阪式, Keihan-shiki?), though Kyūshū-type dialects form a smaller third group. Within each type are several subdivisions. The Western-type dialects are actually in the central region, with borders roughly formed by Toyama, Kyōto, Hyōgo, and Mie Prefectures; most Shikoku dialects are also Western-type. Dialects further west are actually of the Tokyo type. The final category of dialects are those that are descended from the Eastern dialect of Old Japanese; these dialects are spoken in Hachijojima, Tosa, and very few other locations.
Dialects from peripheral regions, such as Tōhoku or Tsushima, may be unintelligible to speakers from other parts of the country. The several dialects used in Kagoshima in southern Kyūshū are famous for being unintelligible not only to speakers of standard Japanese but to speakers of nearby dialects elsewhere in Kyūshū as well, probably due in part to the Kagoshima dialects' peculiarities of pronunciation, which include the existence of closed syllables (i.e., syllables that end in a consonant, such as /kob/ or /koʔ/ for Standard Japanese /kumo/ "spider"). The vocabulary of Kagoshima dialect is 84% cognate with standard Tokyo dialect. Kansai-ben, a group of dialects from west-central Japan, is spoken by many Japanese; the Osaka dialect in particular is associated with comedy.
The Ryūkyūan languages, while closely related to Japanese, are distinct enough to be considered a separate branch of the Japonic family, and are not dialects of Japanese. They are spoken in the Ryūkyū Islands and in some islands that are politically part of Kagoshima Prefecture. Not only is each language unintelligible to Japanese speakers, but most are unintelligible to those who speak other Ryūkyūan languages.
Recently, Standard Japanese has become prevalent nationwide (including portions of the Ryūkyūan islands like Okinawa) due not only to television and radio, but also to increased mobility within Japan due to its system of roads, railways, and airports. Young people usually speak their local dialect and the standard language, though in most cases, the local dialect is influenced by the standard, and regional versions of "standard" Japanese have local-dialect influence.
