Only the present indicative and subjunctive are at all irregular:

Indicative.
Present.
Sing. 1.Ic eom (bēom)willedōgā
2.ðū eart (bist)wiltdēstgǣst
3.hē is (bið)willedēðgǣð
Plur. 1.wēsind(on)
2.gēwillaðdōðgāð
3.hīe
Subjunctive.
Present.
Sing. 1.Icsīe
2.ðūwilledōgā
3.hē
Plur. 1.wēsīen
2.gēwillendōngān
3.hīe

Note.—The preterit subjunctive of bēon is formed, of course, not from wæs, but from wǣron. See [§ 103, (3)].

Preterit-Present Verbs. (See [§ 19].)

[136.]

These verbs are called Preterit-Present because the present tense (indicative and subjunctive) of each of them is, in form, a strong preterit, the old present having been displaced by the new. They all have weak preterits. Most of the Mn.E. Auxiliary Verbs belong to this class.

witan,wiste,
wisse,		wiston,gewiten,to know [to wit, wot].
āgan,āhte,āhton,āgen (adj.),to possess [owe].
cunnan,cūðe,cūðon,gecunnen,
cūð (adj.),		to know, can [uncouth, cunning].
durran,dorste,dorston,——to dare.
sculan,sceolde,sceoldon,——shall.
magan,meahte,
mihte,		meahton,
mihton,		——to be able, may.
mōtan,mōste,mōston,——may, must.

Note.—The change in meaning from preterit to present, with retention of the preterit form, is not uncommon in other languages. Several examples are found in Latin and Greek (cf. nōvi and οἶδα, I know). Mn.E. has gone further still: āhte and mōste, which had already suffered the loss of their old preterits (āh, mōt), have been forced back again into the present (ought, must). Having exhausted, therefore, the only means of preterit formation known to Germanic, the strong and the weak, it is not likely that either ought or must will ever develop distinct preterit forms.

Conjugation of Preterit-Present Verbs.

[137.]