Do other IE languages use ablaut to indicate verb tense?
It occurs in the verbal systems and has to do with tense, aspect, and changing of parts of speech-hood.
Semitic languages also tend not to have verbal tense, but use aspect instead. Just speculating that some unnamed and unknowable "Semitic" language had an effect on Proto-Germanic seems a bit silly to me. I've seen estimates that as much as one-third of the Germanic lexicon is non-Indo-European. The usual suspect for a sub-stratum language is "Old European" (Vennemann et al.), and another theory is that Germanic started as a pidgin, thence to Creole, and finally a language. The linguist, who came up with the term laryngeal, Hermann Möller also p[ublished a comparative dictionary of Semitic-PIE roots. It's probably up on Google Books at this point.
As for strong verbs: drive and bring seem to have PIE roots.
