Phonological Change

In historical linguistics, phonological change is any sound change which alters the number or distribution of phonemes in a language.

In a typological scheme first systematized by Henry M. Hoenigswald, a historical sound law can only affect a phonological system in one of three ways:

• Conditioned merger (which Hoenigswald calls "primary split"), in which some instances of phoneme A become an existing phoneme B; the number of phonemes does not change, only their distribution.
• Phonemic split (which Hoenigswald calls "secondary split"), in which some instances of A become a new phoneme B; this is phonemic differentiation in which the number of phonemes increases.
• Unconditioned merger, in which all instances of phonemes A and B become A; this is phonemic reduction, in which the number of phonemes decreases.

This classification does not consider mere changes in pronunciation, that is, phonetic change, even chain shifts, in which neither the number nor the distribution of phonemes is affected.