InSlavic languages,iotation (/joʊˈteɪ.ʃən/,/ˌaɪ.oʊˈteɪ.ʃən/) is a form ofpalatalization that occurs when a consonant comes into contact with thepalatal approximant/j/ from the succeeding phoneme. The/j/ is represented byiota (ι) in theearly Cyrillic alphabet and theGreek alphabet on which it is based. For example,ni inEnglishonion has the sound of iotatedn. Iotation is a phenomenon distinct fromSlavic 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 aniotated vowel, i.e. one preceded by a palatal glide/j/. As a result, the consonant becomes partially or completely palatalized.^[1] In many Slavic languages, iotated consonants are called "soft" and the process of iotation is called "softening".

Iotation can result in a partialpalatalization so the centre of the tongue is raised during, and sometimes after, the articulation of the consonant. There can also be a complete sound change to apalatal oralveolo-palatal consonant. This table summarizes the typical outcomes in the modern Slavic languages:

According to most scholars, the period of iotation started approximately in the 5th century, in the era ofProto-Slavic, and it lasted for several centuries, probably into the late Common Slavic dialect differentiation. Here is an example from the early stage:^[1]

• Proto-Slavic *kĭasĭa/kьасьа > Russian, Ukrainian, Macedonian, Bulgarian, Serbianчаша(čaša), Czechčíše, Croatiančaša

In Slavic languages, iotated vowels are preceded by apalatal approximant/j/ before avowel, at the beginning of a word, or between two vowels in the middle of a word, creating a diphthongoid, a partialdiphthong.^[2] In theGreek alphabet, the consonant is represented byiota (ι). For example, theEnglishapple iscognate toRussianяблоко (jabloko), both come fromProto-Indo-European: *h₂ébōl. 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. An exception to this is Bulgarian, which has lost iotation for all front vowels (compared to Russian or Polish, who lost it only before[i]).

As it was invented for the writing of Slavic languages, the originalCyrillic 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 iotated 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 signЬ andhard signЪ) that also induce iotation; in addition,Ь palatalizes precedingconsonant, 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 isiotated. The adjective for aletter formed as aligature of theEarly Cyrillic I (І) and another letter, used to represent iotation, isiotated.^{[citation needed]}. The use of an iotated letter does not necessarily denote iotation. Even an iotated letter following a consonant letter is not iotated in most orthographies, but iotated letters imply iotated pronunciation after vowels andsoft andhard signs as well as in isolation.

In the Cyrillic alphabet, some letter forms are iotated, formed as aligature ofEarly Cyrillic I (І) and a vowel.

In old inscriptions, other iotated letters, even consonants, could be found, but they are not in the regular alphabet.

There are more letters that serve the same function, but theirglyphs are not made in the same way.

Iotated consonants occur as result of iotation. They are represented inIPA with superscriptj after it and inX-SAMPA with apostrophe after it so the pronunciation of iotatedn could be represented as[nʲ] or [n'].

WhenVuk Karadžić reformed theSerbian language, he created new letters to represent iotated consonants.Macedonian uses two of them, but has its own versions for iotatedt andd (resembling the lettersГ andК instead ofТ andД):

• Cyrillic alphabet
• Cyrillic ligatures
• Iotacism
• Palatalization, the historical-linguistic sound change
• Soft sign

• Assimilation (linguistics)
• Cyrillic script

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