In Slavic languages, iotation (/joʊˈteɪʃən/) is a form of palatalization that occurs when a consonant comes into contact with a palatal approximant /j/ from the succeeding morpheme. 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.
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Sound change
Iotation occurs when a labial (/m/, /b/), dental (/n/, /s/, /l/) or velar (/k/, /g/, /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:
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:
Iotified vowels
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. This process is still partially productive in some rural areas.
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, which is why iotation and palatalization are often mixed up. There are also two special letters (Ь and Ъ) that prevent that palatalization, but the first one itself palatalizes the consonant again, allowing combinations of both palatalized and nonpalatalized consonants with [j]. Originally, they were super-short vowels [i] and [u] themselves. 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.
In the Cyrillic alphabet, some letter forms are iotified, formed as a ligature of Early Cyrillic I (І) and a vowel.
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.
Iotated consonants
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'].
When Vuk Karadžić reformed the Serbian language, the system still largely influential in Macedonian, he created new letters to represent iotated consonants.