The -er verbs that change stem
CEFR A2 · part 2
edumaterial's parts within the level. The European framework does not subdivide them.
Futur proche or futur simpleChoosing between the two futures and forming the simple one, with its irregular stems…qui, que, où, dontChoosing the relative by its role, and using dont when the verb or noun takes de.meilleur or mieuxComparing with plus, moins and aussi, and choosing between meilleur, an adjective, and…Verbs with à, with de and with nothingKnowing which preposition each verb takes, including the ones that take none.Quantities: beaucoup de, trop de, assez dePutting bare de after any quantity, and knowing when the article does come back.Adverbs and where they goBuilding the adverb from the feminine adjective and placing it after the conjugated verb.The rule, in three lines
They are -er verbs, but the stem changes when the ending stops being pronounced: acheter → j'achète, appeler → j'appelle, préférer → je préfère. It changes in four persons out of six and goes back to the infinitive's in nous and vous.
The usual slip. Conjugating them as if nothing happened: «j'achete», «j'appele», «je prefere». The accent and the double consonant are not decoration.
Why it catches you out. English verbs barely change at all, so every one of these shifts is new to you. And they are not optional spellings: achete is simply a misspelling of achète.