Why some letter pairs are treated as single letters in the alphabet

Ideas & Philosophy · Published 3 October 2026 Swipe more like this →

In short: A digraph is a pair of characters that function as a single unit, representing one sound or a unique sequence. While often just a spelling convention, some languages elevate these pairs to official status, assigning them their own distinct place in the alphabet, separate from their individual constituent parts.

At its core, a digraph is a writing tool used to represent a single phoneme or a specific sound sequence that the individual characters cannot convey alone. These pairs can be homogeneous, such as the doubled letters in 'tapping' or 'cattail', or heterogeneous, like the 'ch' in Spanish or the 'ng' in English. While visual ligatures like 'œ' fuse characters into one, a digraph remains a distinct pairing where the essential feature is the sound produced rather than the visual fusion.

The treatment of these pairs varies wildly across orthographies. In many languages, digraphs are simply combinations of letters. However, in others, they are considered fundamental letters. For instance, in Hungarian, digraphs like 'cs' and 'gy' have dedicated positions in the alphabet, appearing immediately after their primary components. Similarly, Czech and Slovak treat 'ch' as a unique letter following 'h'. This classification is not static; Spanish, for example, formerly treated 'ch' and 'll' as distinct letters but has since moved to split them into their constituent parts for sorting purposes.

Complexity arises when digraphs are not adjacent. English employs 'silent e' to create discontinuous digraphs like 'a_e' in 'cake', a result of historical sound shifts where a final schwa dropped off, leaving the preceding vowel lengthened. Other languages use even more intricate systems, such as the Tatar Cyrillic 'ю...ь' or the Indic alphabets, where vowels may be placed around consonants. These structures challenge our standard definition of a letter, forcing readers to deduce meaning from context or rely on archaic markers like the diaeresis to prevent misinterpretation of adjacent vowels.

Why this matters becomes clear when considering romanization or collation. When a language treats a digraph as a single letter, it fundamentally changes how words are sorted, abbreviated, and hyphenated. Without clear rules, ambiguity is inevitable, leading to systems like the apostrophe in Pinyin or the hyphen in Romansh to distinguish between intended digraphs and accidental letter clusters. Ultimately, the digraph is a testament to the evolution of language, where spelling often lags behind the shifting sounds of human speech.

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