A grapheme (from Greek: γράφω, gráphō, "write") is a fundamental unit in a written language. Examples of graphemes include alphabetic letters, Chinese characters, numerical digits, punctuation marks, and the individual symbols of any of the world's writing systems.
In a fully phonemic orthography, a grapheme corresponds to one phoneme. In English, a grapheme can be composed of more than one letter, for instance digraphs (two letters for a single grapheme) and trigraphs (three letters). For example, the word ship contains three graphemes (sh, i, and p) and three phonemes, because sh is a grapheme that is composed of two letters. Conversely, a single grapheme can represent multiple phonemes, or no phonemes at all in the case of 'silent' letters: the English word "box" has three graphemes, but four phonemes: /ˈbɒks/.
Furthermore, a particular grapheme can represent different phonemes on different occasions, and vice versa. For instance in English the sound /f/ can be represented by 'f', 'ff', 'ph', 'gh' and in some place names of Welsh origin by 'Ff'; while the grapheme 'f' can also represent the phoneme /v/ (as in the word of).
In a script such as Japanese katakana one grapheme corresponds to a syllable (or more technically a mora).
In some languages, a grapheme composed of more than one letter may be treated as a single unit for the purposes of collation, for example in an Hungarian dictionary, words starting in cs come after all other words starting c, while in a Welsh dictionary, words starting ll come after all other words starting in l.
In addition, a single grapheme in print may not correspond to a single grapheme in handwriting, for example in German handwriting the combination ch is usually written quite differently from c + h: given that it also has its own sound value, there is a strong argument for treating this as a single distinct grapheme.
In English and other languages, the choice of grapheme(s) is available to convey morphological relationships, for instance the link between sign and signature is closer in writing than in speech.
Different glyphs can represent the same grapheme, meaning that they are allographs. For example, the lowercase letter a can be seen in two variants: one with a hook at the top and one without (appearing similar to ɑ, the lowercase letter Latin alpha).
In some English personal names and place names, the relationship between the spelling of the name and the pronunciation is so distant that it cannot be identified which phonemes represent which graphemes. Examples are Marjoribanks (pronounced Marshbanks) and Featherstonehaugh (pronounced Fanshaw). Not only that, but in many other words the pronunciation has evolved subsequently to the fixing of the spelling, so that it has to be said that the phoneme(s) represent the grapheme(s), not the other way round. And for many technical jargons, the primary medium of communication is the written language and not the spoken language, so again it is clear that the phoneme(s) represent the grapheme(s).
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