A digraph or digram (from the Greek: δίς dís, "double" and γράφω gráphō, "to write") is a pair of characters used in the orthography of a language to write either a single phoneme (distinct sound), or a sequence of phonemes that does not correspond to the normal values of the two characters combined.
Some digraphs represent phonemes that cannot be represented with a single character in the writing system of a language, like the English sh in ship and fish. Other digraphs represent phonemes that can also be represented by single characters. A digraph that shares its pronunciation with a single character may be a relic from an earlier period of the language when the digraph had a different pronunciation, or may represent a distinction that is made only in certain dialects, like the English wh. Some such digraphs are used for purely etymological reasons, like rh in English. Digraphs are used in some Romanization schemes, like the zh often used to represent the Russian letter ж. As an alternative to digraphs, orthographies and Romanization schemes sometimes use letters with diacritics, like the Czech š, which has the same function as the English digraph sh.
In some languages' orthographies, digraphs (and occasionally trigraphs) are considered individual letters, which means that they have their own place in the alphabet and cannot be separated into their constituent graphemes when sorting, abbreviating or hyphenating words. Examples of this are found in Hungarian (cs, dz, dzs, gy, ly, ny, sz, ty, zs), Czech (ch), Slovak (ch, dz, dž), Albanian (dh, gj, ll, nj, rr, sh, th, xh, zh) and Gaj's Latin alphabet (lj, nj, dž). In Dutch, when the digraph ij is capitalized, both letters are capitalized (IJ).
Digraphs may consist of two different characters (heterogeneous digraphs) or two instances of the same character (homogeneous digraphs). In the latter case, they are generally called double (or doubled) letters.
Doubled vowel letters are commonly used to indicate a long vowel sound. This is the case in Finnish and Estonian, for instance, where ⟨uu⟩ represents a longer version of the vowel denoted by ⟨u⟩, ⟨ää⟩ represents a longer version of the vowel denoted by ⟨ä⟩, and so on. In Middle English, the sequences ⟨ee⟩ and ⟨oo⟩ were used in a similar way, to represent lengthened "e" and "o" sounds respectively; both spellings have been retained in modern English orthography, but the Great Vowel Shift and other historical sound changes mean that the modern pronunciations are quite different from the original ones.
Doubled consonant letters can also be used to indicate a long or geminated consonant sound. In Italian, for example, consonants written double are pronounced longer than single ones. This was the original use of doubled consonant letters in Old English, but during the Middle English and Early Modern English period, phonemic consonant length was lost and a spelling convention developed in which a doubled consonant serves to indicate that a preceding vowel is to be pronounced short. In modern English, for example, the ⟨pp⟩ of tapping differentiates the first vowel sound from that of taping. In rare cases, doubled consonant letters represent a true geminate consonant in modern English; this may occur when two instances of the same consonant come from different morphemes, for example ⟨nn⟩ in unnatural (un+natural).
In some cases, the sound represented by a doubled consonant letter is distinguished in some other way than length from the sound of the corresponding single consonant letter:
In several European writing systems, including the English one, the doubling of the letter ⟨c⟩ or ⟨k⟩ is represented as the heterogeneous digraph ⟨ck⟩ instead of ⟨cc⟩ or ⟨kk⟩ respectively. In native German words, the doubling of ⟨z⟩, which corresponds to /ts/, is replaced by the digraph ⟨tz⟩.
Some languages have a unified orthography with digraphs that represent distinct pronunciations in different dialects (diaphonemes). For example, in Breton there is a digraph ⟨zh⟩ that represents [z] in most dialects, but [h] in Vannetais. Similarly, the Saintongeais dialect of French has a digraph ⟨jh⟩ that represents [h] in words that correspond to [ʒ] in standard French. Similarly, Catalan has a digraph ⟨ix⟩ that represents [ʃ] in Eastern Catalan, but [jʃ] or [js] in Western Catalan–Valencian.
The pair of letters making up a phoneme are not always adjacent. This is the case with English silent e. For example, the sequence a...e has the sound /eɪ/ in English cake. This is the result of three historical sound changes: cake was originally /kakə/, the open syllable /ka/ came to be pronounced with a long vowel, and later the final schwa dropped off, leaving /kaːk/. Later still, the vowel /aː/ became /eɪ/. There are six such digraphs in English, ⟨a—e, e—e, i—e, o—e, u—e, y—e⟩.
However, alphabets may also be designed with discontinuous digraphs. In the Tatar Cyrillic alphabet, for example, the letter ю is used to write both /ju/ and /jy/. Usually the difference is evident from the rest of the word, but when it is not, the sequence ю...ь is used for /jy/, as in юнь /jyn/ 'cheap'.
The Indic alphabets are distinctive for their discontinuous vowels, such as Thai เ...อ /ɤː/ in เกอ /kɤː/. Technically, however, they may be considered diacritics, not full letters; whether they are digraphs is thus a matter of definition.
Some letter pairs should not be interpreted as digraphs but appear because of compounding: hogshead and cooperate. They are often not marked in any way and so must be memorized as exceptions. Some authors, however, indicate it either by breaking up the digraph with a hyphen, as in hogs-head, co-operate, or with a trema mark, as in coöperate, but the use of the diaeresis has declined in English within the last century. When it occurs in names such as Clapham, Townshend and Hartshorne, it is never marked in any way. Positional alternative glyphs may help to disambiguate in certain cases: when round, ⟨s⟩ was used as a final variant of long ⟨ſ⟩, and the English digraph resembling /ʃ/ would always be ⟨ſh⟩.
In romanization of Japanese, the constituent sounds (morae) are usually indicated by digraphs, but some are indicated by a single letter, and some with a trigraph. The case of ambiguity is the syllabic ん, which is written as n (or sometimes m), except before vowels or y where it is followed by an apostrophe as n’. For example, the given name じゅんいちろう is romanized as Jun’ichirō, so that it is parsed as "Jun-i-chi-rou", rather than as "Ju-ni-chi-rou". A similar use of the apostrophe is seen in pinyin where 嫦娥 is written Chang'e because the g belongs to the final (-ang) of the first syllable, not to the initial of the second syllable. Without the apostrophe, Change would be understood as the syllable chan (final -an) followed by the syllable ge (initial g-).
In some languages, certain digraphs and trigraphs are counted as distinct letters in themselves, and assigned to a specific place in the alphabet, separate from that of the sequence of characters that composes them, for purposes of orthography and collation. For example:
Most other languages, including English, French, German, Polish, etc., treat digraphs as combinations of separate letters for alphabetization purposes.
English has both homogeneous digraphs (doubled letters) and heterogeneous digraphs (digraphs consisting of two different letters). Those of the latter type include the following:
Note that in the Cyrillic orthography, those sounds are represented by single letters (љ, њ, џ).
In Norwegian, several sounds can be represented only by a digraph or a combination of letters. They are the most common combinations, but extreme regional differences exists, especially those of the eastern dialects. A noteworthy difference is the aspiration of rs in eastern dialects, where it corresponds to skj and sj. Among many young people, especially in the western regions of Norway and in or around the major cities, the difference between ç and ʃ has been completely wiped away and are now pronounced the same.
The digraphs listed above represent distinct phonemes and are treated as separate letters for collation purposes. On the other hand, the digraphs ⟨mh⟩, ⟨nh⟩, and the trigraph ⟨ngh⟩, which stand for voiceless consonants but occur only at the beginning of words as a result of the nasal mutation, are not treated as separate letters, and thus are not included in the alphabet.
Modern Slavic languages written in the Cyrillic alphabet make little use of digraphs apart from ⟨дж⟩ for /dʐ/, ⟨дз⟩ for /dz/ (in Ukrainian, Belarusian, and Bulgarian), and ⟨жж⟩ and ⟨зж⟩ for the uncommon Russian phoneme /ʑː/. In Russian, the sequences ⟨дж⟩ and ⟨дз⟩ do occur (mainly in loanwords) but are pronounced as combinations of an implosive (sometimes treated as an affricate) and a fricative; implosives are treated as allophones of the plosive /d̪/ and so those sequences are not considered to be digraphs. Cyrillic has few digraphs unless it is used to write non-Slavic languages, especially Caucasian languages.
Because vowels are not generally written, digraphs are rare in abjads like Arabic. For example, if sh were used for š, then the sequence sh could mean either ša or saha. However, digraphs are used for the aspirated and murmured consonants (those spelled with h-digraphs in Latin transcription) in languages of South Asia such as Urdu that are written in the Arabic script by a special form of the letter h, which is used only for aspiration digraphs, as can be seen with the following connecting (kh) and non-connecting (ḍh) consonants:
Ancient Greek also had the "diphthongs" listed above although their pronunciation in ancient times is disputed. In addition Ancient Greek also used the letter γ combined with a velar stop to produce the following digraphs:
Tsakonian has a few additional digraphs: ρζ /ʒ/ (historically perhaps a fricative trill), κχ /kʰ/, τθ /tʰ/, πφ /pʰ/, σχ /ʃ/. In addition, palatal consonants are indicated with the vowel letter ι, which is, however, largely predictable. When /n/ and /l/ are not palatalized before ι, they are written νν and λλ.
In the Hebrew alphabet, תס and תש may sometimes be found for צ /ts/. Modern Hebrew also uses digraphs made with the ׳ symbol for non-native sounds: ג׳ /dʒ/, ז׳ /ʒ/, צ׳ /tʃ/; and other digraphs of letters when it is written without vowels: וו for a consonantal letter ו in the middle of a word, and יי for /aj/ or /aji/, etc., that is, a consonantal letter י in places where it might not have been expected. Yiddish has its own tradition of transcription and so uses different digraphs for some of the same sounds: דז /dz/, זש /ʒ/, טש /tʃ/, and דזש (literally dzš) for /dʒ/, וו /v/, also available as a single Unicode character װ, וי or as a single character in Unicode ױ /oj/, יי or ײ /ej/, and ײַ /aj/. The single-character digraphs are called "ligatures" in Unicode. י may also be used following a consonant to indicate palatalization in Slavic loanwords.
Most Indic scripts have compound vowel diacritics that cannot be predicted from their individual elements. That can be illustrated with Thai in which the diacritic เ, pronounced alone /eː/, modifies the pronunciation of other vowels:
In addition, the combination รร is pronounced /a/ or /am/, there are some words in which the combinations ทร and ศร stand for /s/ and the letter ห, as a prefix to a consonant, changes its tonic class to high, modifying the tone of the syllable.
Two kana may be combined into a CV syllable by subscripting the second; the convention cancels the vowel of the first. That is commonly done for CyV syllables called yōon, as in ひょ hyo ⟨hiyo⟩. They are not digraphs since they retain the normal sequential reading of the two glyphs. However, some obsolete sequences no longer retain that reading, as in くゎ kwa, ぐゎ gwa, and むゎ mwa, now pronounced ka, ga, ma. In addition, non-sequenceable digraphs are used for foreign loans that do not follow normal Japanese assibilation patterns, such as ティ ti, トゥ tu, チェ tye / che, スェ swe, ウィ wi, ツォ tso, ズィ zi. (See katakana and transcription into Japanese for complete tables.)
Long vowels are written by adding the kana for that vowel, in effect doubling it. However, long ō may be written either oo or ou, as in とうきょう toukyou [toːkʲoː] 'Tōkyō'. For dialects that do not distinguish ē and ei, the latter spelling is used for a long e, as in へいせい heisei [heːseː] 'Heisei'. In loanwords, chōonpu, a line following the direction of the text, as in ビール bīru [bi:ru] bīru 'beer'. With the exception of syllables starting with n, doubled consonant sounds are written by prefixing a smaller version of tsu (written っ and ッ in hiragana and katakana respectively), as in きって kitte 'stamp'. Consonants beginning with n use the kana n character (written ん or ン) as a prefix instead.
There are several conventions of Okinawan kana that involve subscript digraphs or ligatures. For instance, in the University of the Ryukyu's system, ウ is /ʔu/, ヲ is /o/, but ヲゥ is /u/.
As was the case in Greek, Korean has vowels descended from diphthongs that are still written with two letters. Those digraphs, ㅐ /ɛ/ and ㅔ /e/ (also ㅒ /jɛ/, ㅖ /je/), and in some dialects ㅚ /ø/ and ㅟ /y/, all end in historical ㅣ /i/.
Hangul was designed with a digraph series to represent the "muddy" consonants: ㅃ *[b], ㄸ *[d], ㅉ *[dz], ㄲ *[ɡ], ㅆ *[z], ㆅ *[ɣ]; also ᅇ, with an uncertain value. Those values are now obsolete, but most of the doubled letters were resurrected in the 19th century to write consonants that did not exist when hangul was devised: ㅃ /p͈/, ㄸ /t͈/, ㅉ /t͈ɕ/, ㄲ /k͈/, ㅆ /s͈/.
Digraphs sometimes come to be written as a single ligature. Over time, the ligatures may evolve into new letters or letters with diacritics. For example sz became ß in German, and "nn" became ñ in Spanish.
Generally, a digraph is simply represented using two characters in Unicode. However, for various reasons, Unicode sometimes provides a separate code point for a digraph, encoded as a single character.