Stem-changing verbs change a vowel in their stem when they are conjugated in certain forms, which affects their pronunciation and meaning. This feature appears mainly in the present tense, preterite tense for some verbs, and other moods like the subjunctive.
Types of Stem Changes
There are three common types of stem changes in Spanish: e to ie, o to ue, and e to i. Each change affects the vowel in the stem for all forms except for the nosotros and vosotros forms.
e to ie
Verbs that change e to ie replace the stem vowel e with ie in stressed syllables when conjugated, so forms like yo, tú, él, ella, ellos, and ellas show the change while nosotros and vosotros keep the original e.
o to ue
Verbs that change o to ue replace the stem vowel o with ue in stressed syllables for most forms, so you see the change in yo, tú, él, ella, ellos, and ellas, but not in nosotros or vosotros.
e to i
Verbs that change e to i replace the stem vowel e with i in stressed syllables for certain forms; this change commonly appears in verbs like pedir, servir and repetir and affects yo, tú, él, ella, ellos, and ellas forms but not nosotros or vosotros.
Verbs That Change in the Preterite
Some stem-changing verbs change in the preterite tense only in the third person forms (él, ella, usted, ellos, ellas, ustedes) and often undergo an e to i or o to u change; these changes occur in verbs like dormir, pedir, preferir, servir, morir and repetir.
Summary
Stem-changing verbs consistently change a vowel in the stem for certain forms to signal meaning and pronunciation differences, with typical patterns of e to ie, o to ue, and e to i that learners should practice in the present tense and note exceptions in the preterite.
Last updated: Fri Oct 24, 2025