In Modern English we classify verbs as regular or irregular. In Old English they were classified as strong or weak.
Nicely put, Faldage. The thing about strong and weak verbs (which runs throughout Germanic languages) is that they both started out a regular phonological processes that have been obscured by other changes. Strong verbs like sing change the quality of their vowel to differentiate between forms, e.g., sing ~ sang, but weak verbs like love simply make due with a suffix, love ~ loved (spelled -t in some verbs). This process is related to an earlier one in Proto-Indoeuropean (the hypothetically reconstructed mother language of most of the European and some of the Iranian and Indian languages) called ablaut. And that had to do with the accentuation of words (and perhaps the movement from a tone system (like Lithuanian) to a stress system (like English).
Verbs like bring ~ braught, think, thought, are sometimes called mixed, because they involve a vowel change and a suffix. But their vowel changes are due to other influences.
Dive is a weak verb that recently people have been treating like a strong one: dive ~ dived vs dive ~ dove. Wear and spit also were originally weak verbs, but are now strong. That having been said, almost any new verbs that come into the language are put in the weak category and made pretty regular.
