Because it is the stem of the verb that changes, these verbs are called stem‐changing verbs or stem‐changers. It is impossible to identify that a verb is a stem‐changer simply by looking at the infinitive unless you have previously learned this particular verb and remember that it is a stem‐changer.
Stem‐changing verbs could be – ar, –er, or – ir verbs. You can, at least, count on the stressed syllable in the stem being the one that changes. Stem‐changing verbs are so common that most dictionaries give the stem change up front in the entry, even before the verb's translation.
The hardest part about stem‐changers is that you have to memorize the verbs that have stem changes. Once you memorize the type of stem change a verb has, the actual patterns of the stem‐changing verbs are quite simple, and all the endings are regular, so conjugating these verbs is easy.
There are basically three ways that the stem of a verb can change in the present tense. The verbs covered in this section are grouped according to the type of stem change they have. While you learn the meanings of the verbs, learn what kind of stem change it has as well.
E to ie
The most common stem change is e to ie (represented by e>ie) . That means the stressed letter e in the stem of the verb will change to ie in certain conjugated forms of the verb. These stem‐changing verbs are listed with the stem change in parentheses after the infinitive. You should remember the verbs with the e>ie as a part of the infinitive so that you'll be able to conjugate them correctly. If a verb has two e's in the stem, it is always the second e that stem changes. In the tables in this section, the e that changes to ie is underlined.
The patterns for stem‐changing verbs are very consistent. All forms of the verb will stem change except for nosotros/nosotras and vosotros/vosotras. The best way to see the patterns is to consider a few examples.
The verb pensar (to think) is typical of an – ar verb with an e>ie stem change. Where the stem change occurs, the ie is underlined in Table 1. Notice that pensamos and pensáis do not have a stem change.
The following list contains commonly used – ar verbs that stem change e>ie exactly like pensar:
The verb p e rder (to lose) is a typical – er verb with an e>ie stem change. The forms of this verb are presented in Table 2, which serves as an model for the list of common –er verbs that follow the table.
The following list presents common ‐ er verbs that stem change e>ie:
The –ir verbs that stem change e>ie all follow the same patterns as the verb mentir (to lie [to tell an untruth]). See Table 4 for the forms of the verb.
The following are some of the most common – ir verbs that have an e>ie stem change:
Tener (to have) and venir (to come) are e>ie stem changers but also have an irregular yo form. You encountered these two verbs with the –go verbs earlier in “Irregular verbs in the yo form.” That is because the yo form of each of these verbs ends in – go, even though the rest of the forms follow the e>ie stem‐changing patterns. These verbs are very common, so be sure to learn the conjugation charts in Tables 6 and 7.
Notice how similar the forms are for both tener and venir. The only differences are in the nosotros/nosotras and vosotros/vosotras endings because venir is an – ir verb and tener is an – er verb.
O to ue
The second most common type of stem change is o to ue (o>ue). Here are some common – ar verbs that stem change o>ue:
Common – er verbs that stem change o>ue are:
Table 8 shows the conjugation forms for the verb poder (to be able). Those verb forms can be followed for the other common –er verbs as well.
Common ‐ ir verbs that stem change o>ue are:
Table 9 shows the conjugation forms for the verb promover (to move). Those verb forms can be followed for the other common – er verbs as well.
The verb jugar is usually listed with the o>ue stem‐changing verbs because it follows the same pattern. However, as you can see, there is no o to change to ue in the verb jugar. It is the only u>ue stem changer in the language. Jugar means “to play a sport,” so of course it's a popular word in both Spanish‐ and English‐speaking cultures. Table 10 shows the unusual verb forms of jugar.
E to i
Contemplate this rule: All e>i stem changing verbs are –ir verbs, but not all – ir verbs are e>i stem changers. Consider the list of e>ie stem changers, some of them are –ir verbs.
This means that when you learn an – ir verb that stem changes, you must remember whether it stem changes e>ie or e>i. Fortunately, the list of e>i stem‐changing verbs is short, and only – ir verbs can stem change e>i.
Common e>i stem changing verbs are:
Table 11 shows the forms of the verb servir (to serve). Use this table as a model for all –ir verbs that are e>i stem changers.