Chain shift

In historical linguistics, a chain shift is a set of sound changes affecting a group of phonemes in the following way: as the pronunciation of one phoneme changes away from its original value, a second phoneme changes toward the original pronunciation of the first phoneme. The sounds involved in a chain shift can be ordered into a "chain" in such a way that, after the change is complete, each phoneme ends up sounding like what the phoneme before it in the chain sounded like before the change. The changes making up a chain shift, interpreted as rules of phonology, are in what is termed counterfeeding order.

For example, if in some language the three vowel phonemes /æ ɛ e/ undergo a change so they became respectively /ɛ e i/, those three changes would constitute a chain shift and could be summarized as

A drag chain or pull chain is a chain shift in which the phoneme at the "leading" edge of the chain changes first. In this example, the chain shift would be a pull chain if /e/ changed to /i/ first, opening up a space at the position of [e] which /ɛ/ then moved to fill. A push chain is a chain shift in which the phoneme at the "end" of the chain moves first: in this example, if /æ/ moved toward [ɛ], creating a "crowding" effect and causing /ɛ/ to move toward [e], and so forth.

A well-known chain shift in the history of English is the Great Vowel Shift of the 15th century, which can be summarized as follows:

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