 The "Grammar" is noted for its comprehensiveness, method and fullness of detail, with all his points illustrated by an almost exhaustive mass of material, and it has served as a model for all succeeding investigators.Diez's grammar of the Romance languages is founded entirely on Grimm's methods, which have had a profound influence on the wider study of the Indo-European languages in general.Jacob is recognized for enunciating Grimm's law, the Germanic Sound Shift, which was first observed by the Danish philologist Rasmus Christian Rask.