Klingenheben's law

In historical linguistics, Klingenheben's law is a set of four sound changes governing the lenition (softening) of certain syllable-final consonants in earlier forms of the Hausa language. The four sound changes affect the velar stops, coronal stops, labial obstruents, and the bilabial nasal. Only the first two are universal to all dialects of the language. The affected consonants were lenited in syllable-final position when followed by a syllable-initial consonant. When other morphophonological changes affected the position of that consonant within a syllable, namely shifting it from the end of one syllable to the beginning of the following syllable, the law no longer applied, leading to phonological alternation.

Klingenheben's law has been employed as an example of geminate inalterability, a process which explains the exceptional behavior of geminate consonants in certain contexts. It is considered one of the two most important sound laws governing Hausa's consonantal inventory and syllable structure, the other being the law of codas in reduplication; these two phenomena were once considered part of the same process. The law is named for the German Africanist August Klingenheben who first described the process in the late 1920s.