This stem change works exactly like the e → i pattern on the previous page, but for a vowel: o becomes u in the third-person singular and third-person plural preterite forms. It only affects -ir verbs, and in practice, there are really just two common verbs to remember.
The Two Verbs
| Infinitive | Meaning |
|---|---|
| dormir | to sleep |
| morir | to die |
That is it. Other common -ir verbs with o in the stem are rare, so these two cover almost everything you will encounter. Their endings are the regular -er/-ir preterite endings; only the stem vowel changes in the third-person forms.
dormir
| Subject | dormir |
|---|---|
| yo | dormí |
| tú | dormiste |
| él / ella / usted | durmió |
| nosotros / nosotras | dormimos |
| ellos / ellas / ustedes | durmieron |
Notice that the stem vowel is o in dormí, dormiste, dormimos but u in durmió, durmieron. The endings themselves are the standard -er/-ir preterite endings.
El bebé durmió ocho horas seguidas.
The baby slept eight straight hours.
morir
| Subject | morir |
|---|---|
| yo | morí |
| tú | moriste |
| él / ella / usted | murió |
| nosotros / nosotras | morimos |
| ellos / ellas / ustedes | murieron |
Mi bisabuelo murió en 1982.
My great-grandfather died in 1982.
Same Scope as E to I
Just like the e → i pattern, the stem change is limited to two forms only:
- 3rd person singular (él / ella / usted)
- 3rd person plural (ellos / ellas / ustedes)
Everything else keeps the original o. Do not say *durmí or *murimos; those are not words.
| Form | Correct | Wrong |
|---|---|---|
| yo | dormí | *durmí |
| tú | dormiste | *durmiste |
| nosotros | dormimos | *durmimos |
| él | durmió | *dormió |
| ellos | durmieron | *dormieron |
Compound and Reflexive Uses
Dormir is often used reflexively as dormirse (to fall asleep). The reflexive pronoun sits before the verb as usual, and the stem change still only hits the third-person forms.
Me dormí en el sofá.
I fell asleep on the couch.
Ella se durmió durante la película.
She fell asleep during the movie.
Los estudiantes se durmieron en clase.
The students fell asleep in class.
Quick Comparison
Put durmió and murieron next to their e → i cousins and you can see the pattern at a glance.
| Verb | 3rd sg. | 3rd pl. |
|---|---|---|
| pedir | pidió | pidieron |
| dormir | durmió | durmieron |
| sentir | sintió | sintieron |
| morir | murió | murieron |
Common mistakes
❌ Yo durmí muy bien anoche.
Wrong: the stem change only happens in the third person.
✅ Yo dormí muy bien anoche.
Correct: the yo form keeps the original o.
❌ El bebé dormió ocho horas.
Wrong: the third-person form must change o → u.
✅ El bebé durmió ocho horas.
Correct: durmió with the stem change in the third person.
❌ Nosotros durmimos hasta tarde.
Wrong: nosotros does not stem-change in the preterite.
✅ Nosotros dormimos hasta tarde.
Correct: dormimos keeps the original o.
❌ Muchas plantas morieron por la sequía.
Wrong: the third-person plural must change o → u.
✅ Muchas plantas murieron por la sequía.
Correct: murieron with the o → u stem change.
Related Topics
- Stem Change: E to IB1 — Stem-changing -ir verbs with e in the stem shift to i in the third-person preterite forms: pidió, pidieron.
- Regular -er and -ir VerbsA2 — Regular -er and -ir verbs share one set of preterite endings: -í, -iste, -ió, -imos, -ieron.
- Irregular GerundsA2 — Stem-changing -ir verbs and verbs with a vowel before the ending form special gerunds like durmiendo, pidiendo, and leyendo.