The OED defines “grapheme” (dating to 1935) as:
The class of letters and other visual symbols that represent a phoneme or cluster of phonemes, as e.g. the grapheme f consists of the ALLOGRAPHS f, ff, F, Ff, gh, ph, and Ph which represent the phoneme /f/ in fun, huffy, Fingal, Ffoulkes, cough, graph, and Philip respectively; so, in a given writing system of a given language, a feature of written expression that cannot be analysed into smaller meaningful units.
This is basically the same as today’s definition from Merriam-Webster, which reads:
1 : a unit (as a letter or digraph) of a writing system
2 : the set of units of a writing system (as letters and letter combinations) that represent a phoneme
Derrida states that “only hidden letters can thus get Socrates moving” (71). Although he is referring to “the text” as Socrates’ pharmakon here, I found it interesting that he later mentioned graphemes. Though a text is actual letters/words on a page, a digraph (which is a kind of grapheme)is in a sense a set of “hidden letters.” Combined letters (\\t\\ + \\sh\\ = “ch”, as M-W.com puts it) that aren’t actually there create the sound of the ones that are.
1 year ago