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Stem-Changing Verbs

Normally the conjugated forms of present-tense verbs retain the same vowels as found in the stems of the infinitives. The conjugated forms of hablar are hablo, hablas, habla, hablamos, habláis, and hablan. Notice that they suffer no stem-change. A number of verbs in Spanish, however, alter the spelling of their stem in their conjugated forms. For example, the infinitive tener, with "e" in its stem, becomes tiene, with "ie" in its stem.

Present Tense

In the present tense there are three vowel transformations with many verbs when the stem is stressed, and they are:

 e –> ie (tener, venir, empezar, comenzar, entender, perder, pensar, herir, hervir, etc.)

 o/u –> eu (dormir, almorzar, acordar, recordar, volver, jugar, etc.)

 e –> i (pedir, servir, medir, teñir, etc.)

Some examples of these changes are as follow:

e > ie

o/u > ue

e > i

*Note the absence of the stem-change in the unstressed "nosotros" and "vosotros" stems.

Preterite Tense

While -ar and -er verb stems change in the present indicative tense, they do not change in any other tense. On the other hand, -ir verbs do change in the preterite tense, but only in the third-person singular and plural forms, and the changes are as follow:

 e > i  (pedir, servir, medir, teñir, preferir, reír, sentir, etc.)

 o > u (dormir, morir, etc.)

Examples:

e > i

o > u

*Note that the only stem-change occurs in the third-person singular and plural forms.

Gerund

The e > i as well as the o > u stem-changes also occur in the gerund or present participle forms of the verbs of the previous section. That is:

pedir –> pidiendo

sentir –> sintiendo

dormir –> durmiendo

morir –> muriendo

See also

Irregular verbs in the future and conditional
Irregular verbs in the imperfect
Irregular verbs in the present
Irregular verbs in the preterite
Irregular verbs in the subjunctive
Verbs