Verbs are traditionally classified into three groups according to the ending of their infinitive.
The verbs être and avoir are verbs that have many peculiarities in their conjugation: they do not belong to any group.
It consists of verbs ending in -er (except for aller). These verbs have a regular conjugation, and most of them follow the pattern of the verb marcher, except for a few verbs that have a particular conjugation:
It consists of verbs ending in -ir and forming their present participle in –issant. These verbs have a regular conjugation, and follow the pattern of the verb finir. Examples : finir, choisir, impartir, bénir, s'agir, rassir. Maudire is part of the 2nd group despite its ending in « -ire ».
This group includes all the verbs that cannot be classified in the first or second group. It includes verbs with irregular conjugations that end, for the most part, in -re and -oir. These verbs are characterized by variable stems (sai-, sav-, sach-, saur- are the stems used in the conjugation of savoir) Verbs ending in -ir with present participle ending in -ant belong to the 3rd group. The verb aller also belongs to this group. Examples : aller, faire, prendre, dire, croire, naître, vendre, voir, pouvoir, vouloir, devoir, courir, partir, mentir.
Each simple form consists of a stem to which an ending is added.
The stem is the part that carries the meaning of the verb. The majority of verbs have only one stem, this is the case of the regular verbs of the 1st and 2nd group.
The ending is the part of the verb that, added to the stem, bears the marks of mode, tense, number and person.
To learn more about French verbs visit the French Grammar online website.