In Slavic languages, iotation (//, //) is a form of palatalization that occurs when a consonant comes into contact with a palatal approximant /j/ from the succeeding phoneme. The /j/ is represented by iota (ι) in the Cyrillic alphabet and the Greek alphabet on which it is based. For example, ni in English onion has the sound of iotated n. Iotation is a distinct phenomenon from Slavic first palatalization in which only the front vowels are involved, but the final result is similar.
Iotation occurs when a labial (/m/, /b/), dental (/n/, /s/, /l/) or velar (/k/, /ɡ/, /x/) consonant comes into contact with a iotified vowel, i.e. one preceded by a palatal glide /j/. As result, the consonant becomes partially or completely palatalized. In many Slavic languages, iotated consonants are called "soft" and the process of iotation is called "softening".
Iotation can result in a partial palatalization so the centre of the tongue is raised during and after the articulation of the consonant. There can also be a complete sound change to a palatal or alveolo-palatal consonant. This table summarizes the typical outcomes in the modern Slavic languages:
|m||mʲ||mj, mʎ||n||nʲ||ɲ||k||kʲ||c, t͡ɕ, t͡ʃ|
|p||pʲ||pj, pʎ||t||tʲ||c, t͡ɕ, t͡ʃ||ɡ||ɡʲ||ɟ, d͡ʑ, d͡ʒ|
|b||bʲ||bj, bʎ||d||dʲ||ɟ, d͡ʑ, d͡ʒ||x||xʲ||ç, ɕ, ʃ|
|f||fʲ||fj, fʎ||s||sʲ||ɕ, ʃ||ɣ||ɣʲ||ʝ, ʑ, ʒ|
|v||vʲ||vj, vʎ||z||zʲ||ʑ, ʒ||h||hʲ||ç, ɕ|
According to most scholars, the period of iotation started approximately in the 5th century, in the era of Proto-Slavic, and it lasted for several centuries, probably into the late Common Slavic dialect differentiation. Here are examples from the early stage:
In Slavic languages, iotified vowels are preceded by a palatal approximant /j/ before a vowel, at the beginning of a word, or between two vowels in the middle of a word, creating a diphthongoid, a partial diphthong. In the Greek alphabet, the consonant is represented by iota (ι). For example, the English apple is cognate to Russian яблоко (jabloko): both come from Proto-Indo-European stem *ābol-. As a result of the phenomenon, no native Slavic root starts with an [e] or an [a] but only with a [je] and [ja]; although other vowels are possible.
As it was invented for the writing of Slavic languages, the original Cyrillic alphabet has relatively complex ways for representing iotation by devoting an entire class of letters to deal with the issue. There are letters which represent iotified vowels; the same letters also palatalize preceding consonants (with or without self-iotation), which is why iotation and palatalization are often mixed up. There are also two special letters (soft sign Ь and hard sign Ъ) that also induce iotation; in addition, Ь palatalizes preceding consonant, allowing combinations of both palatalized (soft) and plain (hard) consonants with [j]. Originally, these letters produced short vowels [i] and [u]. The exact use depends on the language.
The adjective for a phone which undergoes iotation is iotated. The adjective for a letter formed as a ligature of the Early Cyrillic I (І) and another letter, used to represent iotation, is iotified.. The use of a iotified letter does not necessarily denote iotation. Even a iotified letter following a consonant letter is not iotated in most orthographies, but iotified letters imply iotated pronunciation after vowels, soft and hard signs as well as in isolation
|A||А||/a/||Iotified A||Ꙗ||/ja/||Now supplanted by Ya (Я)|
|E||Е||/e/||Iotified E||Ѥ||/je/||No longer used|
|Uk||ОУ||/u/||Iotified Uk||Ю||/ju/||Uk is an archaic form of U (У)|
|Little Yus||Ѧ||/ẽ/||Iotified Little Yus||Ѩ||/jẽ/||No longer used|
|Big Yus||Ѫ||/õ/||Iotified Big Yus||Ѭ||/jõ/||No longer used|
In old inscriptions, other iotified letters, even consonants, could be found, but they are not in the regular alphabet.
There are more letters that serve the same function, but their glyphs are not made in the same way.
|A||Аа||/a/||Ya||Яя||/ja/||Common for East Slavic alphabets|
|E||Ээ||/e/||Ye||Ее||/je/||Used in Belarusian and Russian|
|E||Ее||Ye||Єє||Used in Ukrainian|
|I||Іi||/i/||Yi||Її||/ji/||Used in Ukrainian|
|O||Оо||/o/||Yo||Ёё||/jo/||The latter is used in Belarusian and Russian, in Ukrainian the digraph "Йо" is used instead|
|U||Уу||/u/||Yu||Юю||/ju/||Common for East Slavic alphabets|
Iotated consonants occur as result of iotation. They are represented in IPA with superscript j after it and in X-SAMPA with apostrophe after it so the pronunciation of iotated n could be represented as [nʲ] or [n'].