Kluge's law

Kluge's law is a controversial Proto-Germanic sound law formulated by Friedrich Kluge. It purports to explain the origin of the Proto-Germanic long consonants *kk, *tt, and *pp (Proto-Indo-European lacked a phonemic length distinction for consonants) as originating in the assimilation of *n to a preceding voiced plosive consonant, under the condition that the *n was part of a suffix which was stressed in the ancestral Proto-Indo-European (PIE). The name "Kluge's law" was coined by Kauffmann (1887) and revived by Frederik Kortlandt (1991). As of 2006, this law has not been generally accepted by historical linguists.

The resulting long consonants would subsequently have been shortened, except when they followed a short vowel; this is uncontroversial for *ss (which has a different origin). Proponents of Kluge's law use this to explain why so many Proto-Germanic roots (especially of strong verbs) end in short *p, *t or *k even though their likely cognates in other Indo-European languages point to final Proto-Indo-European (PIE) consonants other than the expected *b, *d, *g or *ǵ. (Indeed, non-Germanic evidence for PIE *b is so rare that *b may not have been a phoneme at all; yet, in Proto-Germanic, *p was only rare at the beginnings of words.)

Much like Verner's law, Kluge's law would have created many consonant alternations in the grammatical paradigm of a word that were soon only partially predictable anymore. Analogical simplifications of these complexities are proposed as an explanation for the many cases where closely related (often otherwise identical) words point to short, long, plosive, fricative, voiceless or voiced Proto-Germanic consonants in closely related Germanic languages or dialects, even sometimes the same dialect.

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