A diaphoneme is an abstract phonological unit that identifies a correspondence between related sounds of two or more varieties of a language or language cluster. For example, some English varieties contrast the vowel of late () with that of wait or eight (). Other English varieties contrast the vowel of late or wait () with that of eight (). This non-overlapping pair of phonemes from two different varieties can be reconciled by positing three different diaphonemes: A first diaphoneme for words like late (), a second diaphoneme for words like wait (), and a third diaphoneme for words like eight (). Diaphonology studies the realization of diaphones across dialects, and is important if an orthography is to be adequate for more than one dialect of a language. In historical linguistics, it is concerned with the reflexes of an ancestral phoneme as a language splits into dialects, such as the modern realizations of Old English . The concept goes back to the 1930s. The word diaphone was originally used with the same meaning as diaphoneme, but was later repurposed to refer to any of the particular variants, making the relationship between diaphoneme and diaphone analogous to that between phoneme and allophone. Usage The term diaphone first appeared in usage by phoneticians like Daniel Jones and Harold E. Palmer. Jones, who was more interested in transcription and coping with dialectal variation than with how cognitively real the phenomenon is, originally used diaphone to refer to the family of sounds that are realized differently depending on dialect but that speakers consider to be the same; an individual dialect or speaker's realization of this diaphone was called a diaphonic variant. Because of confusion related to usage, Jones later coined the term diaphoneme to refer to his earlier sense of diaphone (the class of sounds) and used diaphone to refer to the variants. A diaphonemic inventory is a specific diasystem (a term popularized by Uriel Weinreich) that superimposes dialectal contrasts to access all contrasts in all dialects that are included. This consists of a shared core inventory and, when accounting for contrasts not made by all dialects (whether they are historical contrasts that have been lost or innovative ones not made in all varieties ), only as many contrasts as are needed. The diaphonemic approach gets away from the assumption that linguistic communities are homogeneous, allows multiple varieties to be described in the same terms