The present tense of may, can, shall, is an old strong past. Hence the first and third persons singular are alike:—I may, he may. The actual past tenses of these verbs are weak forms:—might, could, should. Must is the weak past tense of an obsolete mōt, and is almost always used as a present tense.
Dare and owe originally belonged to this class. Owe has become
a regular weak verb, except for the peculiar past tense ought, which
is used in a present sense; dare has in the third person
dare or dares, and in the past dared, more rarely durst.
The archaic wot “know,” past wist, also belongs to this class. Will is inflected like shall, having will in the first and third singular, wilt in the second singular, and would in the past.