In linguistics, a grapheme is the smallest unit of a writing system of any given language. An individual grapheme may or may not carry meaning by itself, and may or may not correspond to a single phoneme of the spoken language. In other words, a grapheme is a letter or a number (set) of letters that represent a sound (more correctly, phoneme) in a word.
Graphemes include alphabetic letters, typographic ligatures, Chinese characters, numerical digits, punctuation marks, and other individual symbols. A grapheme can also be construed as a graphical sign that independently represents a portion of linguistic material.
The word grapheme, coined in analogy with phoneme, is derived from Ancient Greek (gráph?), meaning 'write', and the suffix -eme by analogy with phoneme and other names of emic units. The study of graphemes is called graphemics.
The concept of graphemes is abstract and similar to the notion in computing of a character. By comparison, a specific shape that represents any particular grapheme in a specific typeface is called a glyph. For example, the grapheme corresponding to the abstract concept of "the Arabic numeral one" has a distinct glyph with identical meaning (an allograph) in each of many typefaces (such as, for example, a serif form as in Times New Roman and a sanserif form as in Helvetica).
Graphemes are often notated within angle brackets: ⟨a⟩, ⟨B⟩, etc. This is analogous to both the slash notation (/a/, /b/) used for phonemes, and the square bracket notation used for phonetic transcriptions ([a], [b]).
In the same way that the surface forms of phonemes are speech sounds or phones (and different phones representing the same phoneme are called allophones), the surface forms of graphemes are glyphs (sometimes "graphs"), namely concrete written representations of symbols, and different glyphs representing the same grapheme are called allographs.
For example, in written English (or other languages using the Latin alphabet), there are two different physical representations of the lowercase letter "a", such as a, ?, etc. Since, however, the substitution of any of them for any other cannot change the meaning of a word, they are considered to be allographs of the same grapheme, which can be written ⟨a⟩. Italic and bold face are also allographic.
There is some disagreement as to whether capital and lower case letters are allographs or distinct graphemes. Capitals are generally found in certain triggering contexts that do not change the meaning of a word: a proper name, for example, or at the beginning of a sentence, or all caps in a newspaper headline. In other contexts, capitalization can determine meaning: compare, for example Polish and polish: the former is a language, the latter is for shining shoes. Some linguists consider digraphs like the ⟨sh⟩ in ship to be distinct graphemes, but these are generally analyzed as sequences of graphemes. Non-stylistic ligatures, however, such as ⟨æ⟩, are distinct graphemes, as are various letters with distinctive diacritics, such as ⟨ç⟩.
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The principal types of phonographic graphemes are logograms, which represent words or morphemes (for example Chinese characters, the ampersand "&" representing the word and, Arabic numerals); syllabic characters, representing syllables (as in Japanese kana); and alphabetic letters, corresponding roughly to phonemes (see next section). For a full discussion of the different types, see Writing system § Functional classification.
Not all graphemes are phonographic (write sounds). There are additional graphemic components used in writing, such as punctuation marks, mathematical symbols, word dividers such as the space, and other typographic symbols. Ancient logographic scripts often used silent determinatives to disambiguate the meaning of a neighboring (non-silent) word.
As mentioned in the previous section, in languages that use alphabetic writing systems, many of the graphemes stand in principle for the phonemes (significant sounds) of the language. In practice, however, the orthographies of such languages entail at least a certain amount of deviation from the ideal of exact grapheme-phoneme correspondence. A phoneme may be represented by a multigraph (sequence of more than one grapheme), as the digraph sh represents a single sound in English (and sometimes a single grapheme may represent more than one phoneme, as with the Russian letter ? or the Spanish c). Some graphemes may not represent any sound at all (like the b in English debt or the h in all Spanish words containing the said letter), and often the rules of correspondence between graphemes and phonemes become complex or irregular, particularly as a result of historical sound changes that are not necessarily reflected in spelling. "Shallow" orthographies such as those of standard Spanish and Finnish have relatively regular (though not always one-to-one) correspondence between graphemes and phonemes, while those of French and English have much less regular correspondence, and are known as deep orthographies.
Multigraphs representing a single phoneme are normally treated as combinations of separate letters, not as graphemes in their own right. However, in some languages a multigraph may be treated as a single unit for the purposes of collation; for example, in a Czech dictionary, the section for words that start with ⟨ch⟩ comes after that for ⟨h⟩. For more examples, see Alphabetical order § Language-specific conventions.