The only right way of thoroughly understanding Chaucer's grammar is by comparing one passage with another, observing how particular expressions occur. This is best done by the proper process of reading the text; but even the usual glossarial indexes will often furnish ready examples. Thus the glossary to the Prioresses Tale gives the following examples:—
'And ther she was honoured as hir oughte'; E 1120.
—'wel more us oughte
Receyven al in gree that god us sent'; E 1150.
The glossary to the Man of Law's Tale gives:—
'Alla goth to his in, and, as him oughte,' &c.; B 1097.
'But that they weren as hem oughte be'; G 1340.
'Wel oughten we to doon al our entente'; G 6.
'Wel oughte us werche, and ydelnes withstonde'; G 14.
As to the spelling of the word, it may be remarked that oghte is the more correct form, because ō answers to A.S. ā, and gh to A.S. h in the A.S. form āhte. But a confusion between the symbols ogh, ugh, and ough soon arose, and all three were merged in the form ough; hence neither ogh nor ugh occurs in modern English. See Skeat, Eng. Etymology, § 333, p. 361.