Multiple sections talk about the phonetic development of Proto-Slavic vowels towards the modern Slavic languages, but it is only the letters that should be the subject of the article. Information on historical phonology, if not directly relevant to usage of the letters, should be moved to other articles.
Phonetically, in Old Church Slavonic little yus represented a nasalized front vowel, possibly [ɛ̃] (like the French in in cinq or Polish ę in kęs), while big yus represents a nasalized back vowel, such as IPA [ɔ̃] (like the French on in bombon or Polish ą in kąt).
Other yus letters like the closed little yus (Ꙙꙙ), iotated closed little yus (Ꙝꙝ) and blended yus (Ꙛꙛ), were also used historically. Closed little yus is found in Old Church Slavonic and Middle Bulgarian manuscripts, where it may be used contrastively with little yus. In the Codex Suprasliensis, for example, little yus represents [jɛ̃] and the closed version represents [ɛ̃].[bettersourceneeded] Blended yus is found in certain Middle Bulgarian manuscripts where it replaces (and eliminates) both little and big yus.[bettersourceneeded]
Name
Modern sources reconstruct the letters' names differently. In many cases, they're referred to as little and big yus, or simply yus: Church Slavonic: юсъ малыи, romanized:jusъ malyi and юсъ большии, jusъ bolьšii. Alternatively, they are reconstructed with the corresponding nasal in place of the ju: ѧсъ, ęsъ and ѫсъ, ǫsъ (iotated variants: ѩсъ, jęsъ; ѭсъ, jǫsъ).
In the oldest Slavic abecedarium, the 11/12th-century Glagolitic Paris Abecedarium (Abecenarium Bulgaricum), the name yus ⟨iuſz⟩ is used for letter Ⱓ (ju, Cyrillic Ю), while Ⱙ (jǫ, Cyr. Ѭ), which is the only letter for a nasal vowel in the abecedarium, is named ⟨hie⟩. It remains unclear if the name yus was originally assigned to Ю or to the nasal vowel(s); if it was the latter, the vowel ǫ would develop into u in Russian, explaining the modern form of the letter name.
Cyrillic little yus (left) and big yus (right); normal forms (above) and iotated (below)Evolution of cursive little yus into ЯHandwritten little yusA beard tax token from 1705 containing Ѧ
All modern Slavic languages that use the Cyrillic alphabet have lost the nasal vowels (at least in their standard varieties), making yus unnecessary.
In Bulgarian and Macedonian
Big yus was a part of the Bulgarian alphabet until 1945. However, by then, in the eastern dialects, the back nasal was pronounced the same way as ъ[ɤ]. Since the new Soviet-sponsored regime wanted to break with the one which it replaced at the end of WWII and closer align the official language with Russian, which was closer to the eastern dialects and had already removed its Big Yus, the western pronunciations were deemed unliterary, and the letter was gone.[citation needed]
There were some Bulgarian and Macedonian dialects spoken around Thessaloniki and Kastoria in northern Greece (Kostur dialect, Solun dialect) that still preserve a nasal pronunciation e.g. [ˈkɤ̃deˈɡrẽdeʃˈmiloˈt͡ʃẽdo] (Къде гредеш, мило чедо?; "Where are you going, dear child?"), which could be spelled pre-reform as "Кѫдѣ грѧдешъ, мило чѧдо?" with big and little yus.
On a visit to Razlog, in Bulgaria's Pirin Macedonia, in 1955, the Russian dialectologist Samuil Bernstein noticed that the nasal pronunciation of words like [ˈrɤ̃ka] (hand), [ˈt͡ʃẽdo] (child) could still be heard from some of the older women of the village. To the younger people, the pronunciation was completely alien; they would think that the old ladies were speaking Modern Greek.
In Russian
In Russia, the little yus came to be pronounced as an iotated /ja/ (я) in the middle or at the end of a word and therefore came to represent that sound also elsewhere;[citation needed] the modern letter я is an adaptation of its cursive form of the 17th century, enshrined by the typographical reform of 1708. (That is also why я in Russian often corresponds to nasalized ę in Polish; cf. Russian пять; Polish pięć.)
In Polish
In Polish, which is a Slavic language written in the Latin alphabet, the letter Ęę has the phonetic value of the little yus, and Ąą has that of the big yus. The iotated forms are written ję and ją, respectively, and softened ię and ią also exist, but both historically stem from the un-iotated little yus. The phonemes written as ę and ą are not directly descended from the original Proto-Slavic vowels that the little and big yus represented - instead they developed after the original nasals merged in Polish and then diverged again, often creating alternating pairs (e.g. ząb – zęby, from Proto-Slavic *zǫbъ – *zǫbi). The following table details the exact correspondences of the present Polish nasals to the Proto-Slavic sounds and the respective sound shifts that took place, demonstrated using same stem alternations:
Little and big yuses can also be found in the Romanian Cyrillic alphabet, used until 1862. Little yus was used for /ja/ and big yus for unknown vowels, transcribed in later Romanian as /ɨ/ and /ə/. Now Romanian uses the Latin alphabet and /ɨ/ is written Îî or Ââ. /ə/ is written as Ăă.
One of the first transcriptions of the big yus as î in Romanian is found in Acatist (1801, Sibiu) by Samuil Micu-Klein.
In Slovak
Little yus in the Slovak alphabet has been substituted by a (desať, načať), e (plesať), iotated ia (žiadať, kliatba, mesiac), ie (bdieť) and ä in several cases (pamäť, päť, svätý). Big yus is transliterated and pronounced as u, or accented ú (budeš, muž, mučeník, ruka, navyknúť, pristúpiť, púť, usnúť). Iotated, and closed iotated form of little yus occur as ja (e.g. jazyk, svoja, javiť, jasle).
In Ruthenian
In Ruthenian language, little yus was used to transcribe the sound ja (as in руска(ѧ) мова ("Ruthenian language") or ѧзыкъ ("language")). This evolved into and corresponded with the letter я in the descendant languages of Belarusian, Ukrainian, and Rusyn.
↑Хабургаев, Г. А. (1986). Старославянский язык. Москва: Просвещение. Кириллическая азбука в сопосталении с византийским уницалом и глаголицей [endpaper].
↑Дуриданов, Иван, ed. (1991). Граматика на старобълграския език. София: Издателство на Българската академия на науките. p.43.
