The verb preferir can be conjugated according to tenses in Spanish. Here we'll give conjugations in the present and in the past. So:
Conjugating this verb
The simple present tense is used to talk about habitual actions or routines. So conjugations of the verb preferir using subject pronouns are the following:
The preterite tense is used to describe actions that took place or were completed at a certain point in the past So conjugations of the verb preferir using subject pronouns are the following:
What takes place in the conjugation that makes this verb a stem-changing verb?
The verb preferir is an irregular verb, so this is what makes this verb a stem-changing verb. So, you must learn by heart conjugations of this type of verbs in Spanish because there is no any rule for this type of verbs that you may follow. This is what makes this language to be difficult, the vast conjugation of verbs.