Some verbs are truly irregular in the present tense because the stem form of the verb morphs into something unrecognizable. Do not think of these verbs as stem changers because they do not follow the patterns that stem‐changing verbs follow. These verbs also do not use the normal preterite endings, but there is a consistent set of endings for all of these irregular verbs.
Some of the most commonly used verbs in the language are irregular in the preterite. This should motivate you to learn these irregular forms. Table 1 is a special group of endings that are used for all of the irregular verbs in the following sections. Notice that there are no written accent marks on any of the forms.
Several of the irregular verbs have a u as part of the stem form of the verb in the preterite even though these verbs do not have a u in their infinitive form. The irregular stem that is listed next to the verbs in the following chart is used for every form of the preterite conjugation. All of the following verbs take the endings from Table 1 to form their preterite conjugation chart.
The verb tener (to have) is extremely common, so memorize the forms of tener in the preterite shown in Table 2. They'll help you remember the patterns of all of the u stem verbs just presented.
Certain verbs have an irregular stem with the letter i in it. It is extremely important to remember that these verbs are not considered stem changers in the preterite tense although some of them may have been stem changers in the present tense. Just like the u‐stem verbs, i‐stem verbs do not follow the rules of a stem‐changing verb in the preterite and do not use the normal endings a stem‐changing verb uses. The verbs in the following list have a completely different stem that is used for every form of the preterite. Because they are irregular, they use the irregular endings from Table 2.
These i‐stem verbs are all conjugated like venir, in the preterite tense, as shown in Table 3.
Even though hacer uses the same endings as venir in the preterite, there's one additional spelling change you have to make on the él, ella, and usted forms of hacer to preserve the soft c sound. As you can see in Table 4, you must change the c to a z in front of the –o ending.
The irregular verbs that end in the letter j use the same endings as the other irregular preterite verbs with one exception. Notice in Table 5 that the third person plural ending of the verb decir is – eron. Any time the irregular stem ends in j, the ellos, ellas, and ustedes endings will lose the letter i and become – jeron.
All the verbs that follow are conjugated like decir:
Very irregular preterite verbs
The really irregular verbs in the preterite follow no patterns and simply must be memorized. The verbs ser (to be) and ir (to go) happen to have identical forms in the preterite. You will be able to tell which verb is being used in the context of a sentence. Table 6 is worth learning because it has the preterite forms of two of the most common verbs in the language.
Ver (to see) and dar (to give) are two verbs that are commonly learned together in the preterite tense because their forms are similar. Ver uses the regular endings for a normal – er verb in the preterite and is only irregular because it does not have accent marks. What makes dar strange is that it is conjugated like ver even though it is an – ar verb. Notice that there are no accents on any of the forms in Table 7 (ver) or Table 8 (dar) and that the forms of dar are not the normal forms for an – ar verb.