Épaissir is a french second group verb. So it follow the regular conjugation pattern of the second group like:
conjugation rules and endings for the second group verbs.
Épaissir is conjugated the same way that verbs that end in :
-ir. The prototypical verb for the second conjugation is
finir. The conjugation is, marked by the vowel
i and the infix
-iss- in the indicative present and imperfect.
Épaissir verb is conjugated in interrogative form. For sound reasons, an euphonious
« t » is added to the pronoun of the third person:
« il »,
« elle »,
« on »,
« ils »,
« elles » except when the verb ends with
« t » or
« d »:
« épaissira-t-il ">« aura-t-il épaissi ? ».
Finally, the interrogative form does not exist in subjunctive and imperative.