Exceptions in the construction
For verbs that end in cer, the present form in the 1st person plural is constructed with ç (in order to preserve the soft c sound). This ç remains unchanged in the imparfait (except in the 1st and 2nd person plural).
Example:
lancer – nous lançons
je lançais, tu lançais, il lançait, nous lancions, vous lanciez, ils lançaient
For verbs that end in ger, the present form in the 1st person plural is constructed with e (in order to preserve the soft g sound). This e remains unchanged in the imparfait (except in the 1st and 2nd person plural).
Example:
manger – nous mangeons
je mangeais, tu mangeais, il mangeait, nous mangions, vous mangiez, ils mangeaient
The verbs falloir and pleuvoir, which are only used in the 3rd person singular, are conjugated like this in the imparfait:
Example:
falloir → il fallait
pleuvoir → il pleuvait