Être is the only irregular verb in the imperfect, because the present tense nous sommes has no -ons to drop. So it has the irregular stem ét- and uses the same endings as all other verbs.
As in many other tenses, spelling change verbs, that is, verb which end in -cer and -ger, have minor spelling changes in the imperfect.
Verbs that end in -ier have an imperfect root that ends in i, so end with double i in the nous and vous form of the imperfect. This isn't irregular, but it looks kind of weird.
French imperfect conjugations | ||||||
Here are the imperfect endings and conjugations for the regular verbs parler (to speak) and finir (to finish), the -ier verb étudier (to study), the spelling change verb manger (to eat), and the irregular verb être (to be): | ||||||
| Pronoun | Ending | parler > parl- | finir > finiss- | étudier > étudi- | manger > mange- | être > ét- |
| je (j') | -ais | parlais | finissais | étudiais | mangeais | étais |
| tu | -ais | parlais | finissais | étudiais | mangeais | étais |
| il | -ait | parlait | finissait | étudiait | mangeait | était |
| nous | -ions | parlions | finissions | étudiions | mangions | étions |
| vous | -iez | parliez | finissiez | étudiiez | mangiez | étiez |
| ils | -aient | parlaient | finissaient | étudiaient | mangeaient | étaient |
