|This article does not cite any references or sources. (December 2009)|
|Sound change and alternation|
Progressive metaphony, in which a vowel early in the word influences a subsequent vowel, can be distinguished from regressive metaphony, in which a vowel towards the end of the word influences a preceding vowel. (Progressive metaphony is sometimes called "left-to-right" metaphony, and regressive metaphony may be called "right-to-left" metaphony.)
Progressive metaphony is also called vowel harmony, and is discussed fully in the article under that heading. However, some linguists use the term "vowel harmony" for regressive metaphony too.