Proto-Germanic
Outside the Uralic family, the term consonant gradation has recently been applied to Proto-Germanic, the parent language of the Germanic languages. Consonant gradation is not directly attested in any of the Germanic dialects, but must nevertheless be reconstructed on the basis of certain dialectal discrepancies in root of the n-stems and the ōn-verbs.
Diachronically, the rise of consonant gradation in Germanic is explained by Kluge's law, by which geminates arose from stops followed by a nasal in a stressed syllable. Since this sound law only operated in part of the paradigms of the n-stems and ōn-verbs, it gave rise to an alternation of geminated and non-geminated consonants.
| n-stems | PIE | PGM |
|---|---|---|
| nominative | C_́C-ōn | C_C-ō |
| genitive | C_C-n-ós | C_CC-az |
| neh2-presents | PIE | PGM |
|---|---|---|
| 3p. singular | C_C-néh2-ti | C_CC-ōþi |
| 3p. plural | C_C-nh2-énti | C_G-unanþi |
The reconstruction of grading paradigms in Proto-Germanic explains root alternations such as Old English steorra 'star' < *sterran- vs. Old Frisian stera 'id.' < *steran- and Norwegian (dial.) guva 'to swing' < *gubōn- vs. Middle High German gupfen 'id.' < *guppōn- as generalizations of the original allomorphy. In the cases concerned, this would imply reconstructing an n-stem nom. *sterō, gen. *sterraz < PIE *h2stér-ōn, *h2ster-n-ós and an ōn-verb 3sg. *guppōþi, 3pl. *gubunanþi < *ghubh-néh2-ti, *ghubh-nh2-énti.
Read more about this topic: Consonant Gradation