If a sound changes with reference to a following segment, it is traditionally called "regressive assimilation". Changes with reference to a preceding segment are traditionally called "progressive". ManyFor examples, see: Slis, Iman Hans. 1985. The voiced-voiceless distinction and assimilation of voice in Dutch. Helmond: Wibro. 2-3. find those terms confusing, as they seem to mean the opposite of the intended meaning. Accordingly, a variety of alternative terms have arisen, not all of which avoid the problem of the traditional terms. Regressive assimilation is also known as right-to-left, leading, or anticipatory assimilation. Progressive assimilation is also known as left-to-right, perseveratory, preservative, lagging, or lag assimilation. The terms anticipatory and lag are used here.
