Yes, dormir is an irregular verb in Spanish. It belongs to a category called stem-changing verbs, meaning the “o” in the stem shifts to “ue” or “u” depending on the tense and subject. The good news is that these changes follow a predictable pattern, so once you learn the rules, dormir becomes straightforward to conjugate.
How Dormir Changes in Present Tense
In the present indicative, dormir undergoes an o-to-ue stem change in four of its six forms. The two exceptions are nosotros and vosotros, which keep the original “o” and follow regular -ir endings.
- Yo: duermo
- Tú: duermes
- Él/ella/usted: duerme
- Nosotros: dormimos
- Vosotros: dormís
- Ellos/ellas/ustedes: duermen
This “boot pattern” (so named because the four changed forms create a boot shape on a conjugation chart) is the most common irregularity you’ll encounter with dormir. If you’ve learned other o-to-ue verbs like poder or volver, the logic is identical.
The Preterite Has a Different Stem Change
In the preterite (simple past), dormir changes its stem from “o” to “u,” but only in the third person singular and plural. Every other form uses the regular stem.
- Yo: dormí
- Tú: dormiste
- Él/ella/usted: durmió
- Nosotros: dormimos
- Vosotros: dormisteis
- Ellos/ellas/ustedes: durmieron
This o-to-u shift is easy to overlook because it only affects two forms. But it’s a common test question and a frequent mistake in writing, so it’s worth memorizing separately.
Present Subjunctive: Both Changes Appear
The present subjunctive is where dormir gets slightly more complex, because both stem changes show up in the same tense. The four “boot” forms use the o-to-ue change (just like the present indicative), while nosotros and vosotros use the o-to-u change instead.
- Yo: duerma
- Tú: duermas
- Él/ella/usted: duerma
- Nosotros: durmamos
- Vosotros: durmáis
- Ellos/ellas/ustedes: duerman
This is the only tense where nosotros and vosotros actually change their stem. In every other tense, those two forms stay regular.
The Gerund Also Changes
The present participle (gerund) of dormir is durmiendo, not “dormiendo.” It uses the same o-to-u change you see in the preterite third person. You’ll use this form with estar to express ongoing actions: estoy durmiendo (“I am sleeping”), estás durmiendo (“you are sleeping”), and so on. Since the gerund stays the same regardless of subject, you only need to remember the one form.
Where Dormir Is Actually Regular
Not every tense has irregularities. The future and conditional tenses use the regular dormir stem with standard endings: dormiré, dormirás, dormirá for the future, and dormiría, dormirías, dormiría for the conditional. No stem change at all. The imperfect indicative is also completely regular: dormía, dormías, dormía, and so on. The past participle is dormido, which follows the standard -ir pattern with no surprises.
So while dormir is technically irregular, its irregularities are concentrated in a few specific places: present tense, preterite third person, subjunctive, and the gerund. Outside of those, it behaves like any other -ir verb.
Dormir vs. Dormirse
One thing that trips up learners isn’t the conjugation itself but choosing between dormir and dormirse. Plain dormir means “to sleep” and refers to the ongoing state: dormí ocho horas (“I slept eight hours”). Dormirse means “to fall asleep” and emphasizes the moment of transition: me dormí en el sofá (“I fell asleep on the couch”). The conjugation pattern is identical for both. The reflexive version just adds the pronoun (me, te, se, nos, os, se) in front of or attached to the verb form.
Quick Reference for All the Stem Changes
Here’s a summary of when each change kicks in:
- O → UE: Present indicative (all forms except nosotros/vosotros), present subjunctive (all forms except nosotros/vosotros), affirmative tú command (duerme)
- O → U: Preterite third person (durmió, durmieron), present subjunctive nosotros/vosotros (durmamos, durmáis), gerund (durmiendo), imperfect subjunctive (all forms)
- No change: Future, conditional, imperfect indicative, past participle
Other common verbs that follow this exact same dual stem-change pattern include morir (to die). If you master the pattern with dormir, morir comes free.