Verner's law, stated by Karl Verner in 1875, describes a historical sound change in the Proto-Germanic language whereby voiceless fricatives *f, *þ, *s, *h (including *hʷ ), when immediately following an unstressed syllable in the same word, underwent voicing and became respectively the fricatives *b, *d, *z, *g
Karl Verner was the first scholar to note the factor governing the distribution of the two outcomes. The original location of stress was often retained in Greek and early Sanskrit, though in Germanic stress eventually became fixed on the initial (root) syllable of all words. The crucial difference between *pātḗr and *bʱrā́tēr was therefore one of second-syllable versus first-syllable stress (cf. Sanskrit pitā́ versus bhrā́tā).
