Iotation is a linguistic phenomenon very characteristic of the Slavic languages. It should not be confused with palatalization, which is an entirely different process.
Iotation is an appearance of 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).[1] In the Greek alphabet this consonant is represented by iota (ι), hence the name. For example, the English apple is cognate to Russian яблоко (jabloko); they both come from an Indo-European root *āblu-. As a result of this 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 script has relatively complex ways for representing iotation, devoting an entire class of letters to deal with the issue; there are letters which represent iotified vowels; these 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, thus allowing combinations of both palatalized and non-palatalized consonants with [j]. Originally they were super-short vowels [i] and [u] themselves. The exact use depends on the language; see Cyrillic script as used in Slavic languages.
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 (which is used to represent iotation) is iotified.
In the Cyrillic script, some letter forms are iotified, that is, formed as a ligature of Early Cyrillic I (І) and a vowel.
| Normal | Iotified | Comment | ||||
|---|---|---|---|---|---|---|
| Name | Shape | Sound | Name | Shape | Sound | |
| A | А | /a/ | Iotified A | Ꙗ | /ja/ | Now supplanted by Ja (Я). Often substituted and confused with Ѧ in East Slavic texts. |
| E | Е | /e/ | Iotified E | Ѥ | /je/ | No longer used |
| Uk | Ѹ | /u/ | Iotified Uk | Ю | /ju/ | Uk is an archaic form of U (У) |
| Little Jus | Ѧ | /ẽ/ | Iotified Little Jus | Ѩ | /jẽ/ | No longer used |
| Big Jus | Ѫ | /õ/ | Iotified Big Jus | Ѭ | /jõ/ | No longer used |
| I | І | /i/ | Ji | И | /ji/ | Iotified distinction lost in modern pronunciation |
In old inscriptions, other iotified letters, even consonants, could be found, but these are not parts of a regular alphabet:
| Normal | Iotified | Comment | ||||
|---|---|---|---|---|---|---|
| Name | Shape | Sound | Name | Shape | Sound | |
| Jat | Ѣ | /æ/ | Iotified Jat | Ꙓ | /jæ/ | iotified form is very rare even in manuscripts |
There are more letters which serve the same function, but their glyphs are not made in the same way.
| Normal | Iotified | Comment | ||||
|---|---|---|---|---|---|---|
| Name | Shape | Sound | Name | Shape | Sound | |
| A | А | /a/ | Ja | Я | /ja/ | Used in Bulgarian, Belarusian and Russian |
| E | Э | /e/ | Je | Е | /je/ | Used in Belarusian and Russian |
| E | Е | /e/ | Je | Є | /je/ | Used in Ukrainian |
| I | І | /i/ | Ji | Ї | /ji/ | Used in Ukrainian |
| O | О | /o/ | Jo | Ё | /jo/ | Used in Bulgarian, Belarusian and Russian |