Editing Digraph (orthography) (section)

== Homogeneous digraph{{anchor|Homogeneous digraph}} ==
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 orthography|Finnish]] and [[Estonian orthography|Estonian]], for instance, where {{vr|uu}} represents a longer version of the vowel denoted by {{vr|u}}, {{vr|ää}} represents a longer version of the vowel denoted by {{vr|ä}}, and so on. In [[Middle English orthography|Middle English]], the sequences {{vr|ee}} and {{vr|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 [[Phonological history of English vowels|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 [[gemination|geminated]] consonant sound. In [[Italian orthography|Italian]], for example, consonants written double are pronounced longer than single ones. This was the original use of doubled consonant letters in [[Old English orthography|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 {{vr|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 [[morpheme]]s, for example {{vr|nn}} in ''unnatural'' (''un''+''natural'') or {{vr|tt}} in ''cattail'' (''cat''+''tail'').

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 [[Welsh language|Welsh]] and [[Greenlandic language|Greenlandic]], {{vr|ll}} stands for a voiceless [[lateral consonant]], while in [[Spanish language|Spanish]] and [[Catalan language|Catalan]] it stands for a [[palatal consonant]].
*In several languages of western Europe, including English, [[French language|French]], [[Portuguese language|Portuguese]] and Catalan, the digraph {{angbr|ss}} is used between vowels to represent the voiceless sibilant {{IPA|/s/}}, since an {{angbr|s}} alone between vowels normally represents the voiced sibilant {{IPA|/z/}}.
*In Spanish, Portuguese, Catalan and Basque, [[rr (digraph)|{{vr|rr}}]] is used between vowels for the [[alveolar trill]] {{IPA|/r/}}, since an {{vr|r}} alone between vowels represents an [[alveolar flap]] {{IPA|/ɾ/}} (the two are different phonemes in those languages).
*In Spanish, the digraph {{vr|nn}} formerly indicated {{IPA|/ɲ/}} (a [[palatal nasal]]); it developed into the [[ñ|letter ñ]].
*In [[Basque language|Basque]], double consonant letters generally mark [[Palatalization (phonetics)|palatalized]] versions of the single consonant letter, as in [[dd (digraph)|{{vr|dd}}]], {{vr|ll}}, [[tt (digraph)|{{vr|tt}}]]. However, {{vr|rr}} is a trill that contrasts with the single-letter flap, as in Spanish, and the palatal version of {{vr|n}} is written {{vr|ñ}}.

In several European writing systems, including the English one, the doubling of the letter {{angbr|c}} or {{angbr|k}} is represented as the heterogeneous digraph {{angbr|ck}} instead of {{angbr|cc}} or {{angbr|kk}} respectively. In native German words, the doubling of {{angbr|z}}, which corresponds to {{IPA|/ts/}}, is replaced by the digraph {{angbr|tz}}.