Digraphae

Digraphae is a term used in linguistics and orthography to refer to a sequence of two letters that represent a single sound or phoneme. This contrasts with a trigraph, which is a sequence of three letters representing one sound. Digraphs are common in many writing systems, including the Latin alphabet. They exist to represent sounds that cannot be adequately represented by a single letter in the alphabet.

Examples of digraphs in English include 'sh' as in 'ship', 'ch' as in 'chair', 'th' as in 'thin' and 'this', 'ph' as in 'phone', and 'ck' as in 'back'. Some digraphs are considered "silent" or "diagraphic pairs" where the combination of letters alters the pronunciation of the preceding vowel, such as the 'ea' in 'read' (pronounced differently depending on tense) or the 'ai' in 'rain'. Other digraphs are simply the most common way to represent a particular sound. The use and specific digraphs found vary significantly between languages. For instance, while 'ch' is a digraph in English, in some other languages it might be treated as two separate sounds or a different letter altogether. The study of digraphs is part of phonetics and orthography, contributing to understanding the relationship between written language and spoken sounds.