The difference between weak and strong verbs in English appears to date back to proto-Germanic, where the -d- inflexion arose. It does not appear to be related to weak inflexions in other Indo-European languages: e.g. Greek had a perfect using -k-, and Latin used -v-.

Proto-Indo-European probably didn't have a weak inflexion at all. I've got to admit this is more complicated than I understand and I would need to study several of my geet big thick books some more to get a handle on it. But basically, the sing-sang-sung kind of pattern was regular at the proto-Indo-European level.

It is theorized to derive from pre-Indo-European accent patterns, changing the vowels. I really should know more of this.

P.S. Hi.