Ok, I don't know if anyone here will know the answer to this question, but can anyone clarify what the ablaut was in Indo-European? I know that it changes the stem of a word based on tense verbs and converting from verbs to nouns (and the vice). However, I am not sure if it is only related to tense or if it also effects case. Similarly, does it preserve this same functionality in Proto-Germanic and carry through to Old English (ie: if it does happen to indicate case in IE, does it do the same in PG/OE)?