It was noticed that in some words we find consonants which do not fit into
Grimm’s Law. In some cases it is voiced stops rather than voiceless fricatives, that correspond to IE voiceless stops.
e.g. Lat. pater – Goth. fadar
Greek dekas – Goth. tigus
Explanation of these exceptions was given in 1877 by the Danish scholar Karl Verner. If an IE voiceless stop was preceded by an unstressed vowel, the voiceless fricative which developed from it in accordance with Grimm’s Law, became voiced and later turned into a voiced stop.
So pater > paþer > paðer > fadar
Greek dekás(десяток) – Goth. tigus.
But if the preceding vowel was stressed then changes by Grimm’s Law took place.
Greek décas(десять) – Goth. taihun.
A great number of similar examples can be found in strong verbes.
OE cweðan – cwæð – cwædon; wesan – wæs – wæron
These are not exceptions from Grimm’s Law but results of a further development of consonants resulting from this law.
