Soft sign

The soft sign is normally written after a consonant and indicates its softening (palatalization) (for example Ukrainian батько 'father'). Less commonly, the soft sign just has a grammatically determined usage with no phonetic meaning (like Russian: туш 'fanfare' and тушь 'India ink', both pronounced /tuʂ/ but different in grammatical gender and declension). In East Slavic languages and some other Slavic languages (such as Bulgarian), there are some consonants that do not have phonetically different palatalized forms but corresponding letters still admit the affixing soft sign.

The Serbian Cyrillic alphabet has had no soft sign as a distinct letter since the mid-19th century: palatalization is represented by special consonant letters instead of the sign (some of these letters, such as ⟨Љ⟩ or ⟨Њ⟩, were designed as ligatures with the grapheme of the soft sign). The modern Macedonian alphabet, based on the Serbian Cyrillic variant, has had no soft sign since its creation, in 1944.

Between a consonant and a vowel, the soft sign bears also a function of "iotation sign": in Russian, vowels after the soft sign are iotated (compare Russian льют /lʲjut/ '(they) pour/cast' and лют /lʲut/ '(he is) fierce'). The feature, quite consistent with Russian orthography, promulgated a confusion between palatalization and iotation, especially because ⟨ь⟩ usually precedes so-called soft vowels. Combinations ⟨ья⟩ (ya), ⟨ье⟩ (ye), ⟨ьё⟩ (yo) and ⟨ью⟩ (yu) give iotated vowels, like corresponding vowel letters in isolation (and word-initially), and unlike its use immediately after a consonant letter in which palatalization can occur but not iotation. In those cases, ⟨ь⟩ may be considered as a sign indicating that a vowel after it is pronounced separately from the previous consonant, but that is the case neither for ⟨ьи⟩ (yi) nor for ⟨ьо⟩ (yo), because these vowels are not iotated in isolation. The latter case, though, is rarely used in Russian (only in loanwords such as ⟨бульон⟩) and can be seen as a replacement of phonetically identical ⟨ьё⟩, which gets rid of an "inconvenient" letter ⟨ё⟩. In Ukrainian and Bulgarian, the spelling ⟨ьо⟩ indicates palatalization, not iotation.

⟨ъ⟩, an "unpalatalization sign", also denotes iotation, as in the case of ⟨ъя⟩, ⟨ъе⟩, ⟨ъё⟩ and ⟨ъю⟩ in Russian. It differs from the soft sign in that it doesn't necessarily soften the preceding consonant like the soft sign does (although consonants preceding the hard sign are still sometimes softened).

Similarly, the soft sign may denote iotation in Belarusian and Ukrainian, but it is not used so extensively as in Russian. Ukrainian uses a quite different repertoire of vowel letters from those of Russian and Belarusian, and iotation is usually expressed by an apostrophe in Ukrainian. Still the soft sign is used in Ukrainian if the sound preceded by an iotated vowel is palatalized.

Among Slavic languages using the Cyrillic script, the soft sign has the most limited use in Bulgarian: while phonemic palatalization does occur, it is very limited, even more than in other hard languages like Serbian (compare Bulgarian кон to Russian конь or Serbian коњ). The only possible position is one between consonants and ⟨о⟩ (such as in names Жельо, Кръстьо, and Гьончо, or the word синьо). Rather, the letter is mostly used in foreign words of French or German origin, such as шофьор (driver, chauffeur).

In Slavistic transcription, which is a system used to represent Proto-Slavic language, the Cyrillic letters Ь and Ъ are employed to denote extra-short vowel sounds. Ь represents the extra-short /ĭ/ sound, while Ъ represents the extra-short /ŭ/ sound.

Proto-Slavic refers to the common ancestor of the Slavic languages, which was spoken around the 5th to 9th centuries AD. During this period, the Slavic languages were still in the process of diverging from a shared linguistic ancestor. Slavistic transcription aims to reconstruct the phonological features of Proto-Slavic based on historical and comparative linguistics.

In Old Slavonic orthography, which is closely related to Proto-Slavic, the soft sign (Ь) and the hard sign (Ъ) were originally used to represent the extra-short vowel sounds. These extra-short vowels were distinct from regular short vowels in terms of their duration or length.

The extra-short /ĭ/ sound represented by Ь was a front vowel, similar to the sound of "i" in the English word "bit." On the other hand, the extra-short /ŭ/ sound represented by Ъ was a back vowel, similar to the sound of "u" in the English word "put."

By utilizing Ь and Ъ in Slavistic transcription, linguists and researchers can indicate the presence of these extra-short vowel sounds in reconstructed Proto-Slavic words. This transcription system allows for a more accurate representation of the phonetic and phonological characteristics of the ancestral Slavic language.

In certain non-Slavic Cyrillic-based alphabets, such as Chechen, Ingush, and various Dagestanian languages like Tabasaran, the digraph ⟨аь⟩ is introduced to represent the sounds /æ/ or /a/. This combination of the letter "а" and the soft sign "ь" denotes a specific vowel sound. Similarly, the digraph ⟨оь⟩ is used for /œ/ or /ø/, and ⟨уь⟩ for /y/. Additional iotated forms like ⟨юь⟩ and ⟨яь⟩ are used as needed. This usage of the soft sign is similar to the trailing "e" in German when umlauts are unavailable.

This approach allows for the representation of specific vowel sounds in these non-Slavic languages using the available Cyrillic characters. The soft sign ⟨ь⟩, combined with other letters, creates digraphs to represent distinct phonemes that cannot be expressed by the bare letters alone.

There have also been proposals to use the ⟨аь⟩ digraph in Turkic languages as a replacement for Cyrillic Schwa (Ә), which represents the sound /ə/ or /æ/. Unlike Schwa, which may not be present in all Cyrillic character repertoires, both ⟨а⟩ and ⟨ь⟩ are commonly available letters in the basic modern Russian alphabet.

In addition to its use with vowels, the soft sign, like the hard sign and the palochka, is employed in many languages as digraphs to represent consonant sounds that are phonetically similar but distinct from the bare letter. For example, while the letter "г" represents the sound /g/, the combination "гь" represents /ɣ/ in Crimean Tatar, /ɦ/ in Archi, and /h/ in Avar and Tabasaran.