Grimm's law
Against the theories regarding substrata, a profound sound change in the Germanic languages, Grimm's law, has been put forward as evidence for the Germanic languages being "non-substratic" and having changed, by their own accord, away from other branches of Indo-European. Grimm's law affected all of the stops that were inherited from Proto-Indo-European. The Germanic languages also share common innovations in grammar as well as in phonology: the Germanic verb has been extensively remodelled and shows fewer grammatical moods and markedly fewer inflections for the passive voice.