Spanish Stem-Changing Verbs o→ue

In Brief

In many common Spanish verbs, o in the stem changes to ue when that syllable is stressed: dormir becomes duermo, and volver becomes vuelves. In the present tense, the change appears in every person except nosotros/nosotras and vosotros/vosotras: dormimos, volvéis. The regular present-tense endings stay the same.

Overview

Spanish stem-changing verbs alter a vowel inside the stem (the part left after removing -ar, -er, or -ir from the infinitive, or dictionary form). For example, the stem of volver is volv-. In forms where its o is stressed, volv- becomes vuelv-: vuelvo, vuelves, vuelve. Because the change affects the stem rather than the ending, these are also sometimes called radical-changing verbs.

This pattern matters from A1 onward because it occurs in high-frequency verbs for sleeping, returning, finding, remembering, and telling or counting: dormir, volver, encontrar, recordar, and contar. English does not have one matching conjugation pattern. An English speaker may therefore be tempted either to keep the infinitive stem everywhere (yo dormo) or to change it everywhere (nosotros duermimos). Neither works.

The beginner rule is compact: in the present indicative (the ordinary present used for facts, habits, and current situations), use ue in the “boot” forms—yo, tú, él/ella/usted, and ellos/ellas/ustedes—but keep o with nosotros and vosotros. Subject pronouns are often omitted in Spanish because the ending already identifies the person.

How It Works

Keep the ending; change the stressed stem vowel

Start with the regular present-tense process:

1. Remove the infinitive ending: contar → cont-.
2. Add the normal ending for an -ar, -er, or -ir verb.
3. If the stem syllable containing o is stressed, change o to ue: cont-o → cuento.
4. Do not make the change in nosotros or vosotros, where the ending receives the stress: contamos, contáis.

The spelling ue represents one syllable here. Compare CUEN-to with con-TA-mos: the vowel change tracks the stressed stem in the present-tense pattern.

Person	contar (to count/tell)	volver (to return)	dormir (to sleep)
yo	cuento	vuelvo	duermo
tú	cuentas	vuelves	duermes
él / ella / usted	cuenta	vuelve	duerme
nosotros / nosotras	contamos	volvemos	dormimos
vosotros / vosotras	contáis	volvéis	dormís
ellos / ellas / ustedes	cuentan	vuelven	duermen

The person endings are ordinary endings for each verb class:

Verb class	yo	tú	él/ella/usted	nosotros	vosotros	ellos/ustedes
-ar (contar)	-o	-as	-a	-amos	-áis	-an
-er (volver)	-o	-es	-e	-emos	-éis	-en
-ir (dormir)	-o	-es	-e	-imos	-ís	-en

This separation is useful: the stem change does not create a new set of endings. If you already know regular present-tense verbs, you only need to learn which verbs change and remember where the change occurs.

The “boot” pattern

On a traditional six-cell conjugation chart, the four changed forms surround the two unchanged forms, making a rough boot shape:

	Singular	Plural
First person	cuento	contamos
Second person	cuentas	contáis
Third person	cuenta	cuentan

This memory aid describes the chart, not a grammatical rule of its own. In Latin America, vosotros is generally not used, but the same essential contrast remains: nosotros contamos has no change, while ustedes cuentan does.

Common verbs in this group

Infinitive	Core meaning	Useful present form
dormir	to sleep	duermo
volver	to return, come back	vuelves
encontrar	to find; encounter	encuentra
recordar	to remember; remind	recuerdo
contar	to count; tell	cuentan
poder	can, to be able to	puedo
costar	to cost; be difficult	cuesta
mostrar	to show	muestra
probar	to try, taste, test	pruebo
soñar	to dream	sueña

You cannot safely predict the pattern merely from seeing an o. Regular verbs such as comer and tomar do not become cuemer or tuemar. Learn a stem-changing verb with three anchor forms: infinitive + yo + nosotros—for example, volver, vuelvo, volvemos.

Negatives and questions

Negation and question formation do not alter the conjugation. Put no before the verb for a negative statement: No recuerdo. In writing, direct questions use both opening and closing question marks: ¿Recuerdas su nombre? The subject can follow the verb, but it does not have to: ¿Cuándo vuelve Ana?

Examples in Context

Spanish	English	Note
Duermo ocho horas.	I sleep eight hours.	Yo form of dormir
¿Cuándo vuelves?	When are you coming back?	Tú form of volver
No encuentro las llaves.	I can’t find the keys.	Encontrar often appears in everyday problems
¿Recuerdas su nombre?	Do you remember their name?	Tú form of recordar
Mi hermana vuelve a casa a las seis.	My sister comes home at six.	Third-person singular
Los niños duermen después de comer.	The children sleep after eating.	Third-person plural
Dormimos con la ventana abierta.	We sleep with the window open.	No change with nosotros
¿Volvéis mañana?	Are you all coming back tomorrow?	No change with vosotros
Encontramos una cafetería tranquila.	We find a quiet café.	Unchanged nosotros stem
Marta cuenta el dinero.	Marta counts the money.	Contar meaning “to count”
Siempre cuento la misma historia.	I always tell the same story.	Contar meaning “to tell”
Esta camisa cuesta treinta euros.	This shirt costs thirty euros.	Costar is usually used in the third person for prices
¿Puedes abrir la puerta?	Can you open the door?	Poder + infinitive expresses ability or a request
Probamos el menú del día.	We try the set menu.	No change with nosotros
Sueñan con vivir cerca del mar.	They dream of living near the sea.	Soñar con means “to dream of/about”

English present forms may have several natural Spanish equivalents depending on context. Vuelves can mean “you return,” “you come back,” or, in a suitable context, “you are coming back.” The stem change is the same regardless of the best English translation.

Common Mistakes

Keeping o in a changed form

• Wrong: Yo dormo ocho horas.
• Right: Yo duermo ocho horas.
• Why: The stem vowel is stressed in the yo form, so o changes to ue. The ending is still the regular -o ending.

Changing the nosotros or vosotros form

• Wrong: Nosotros duermimos bien.
• Right: Nosotros dormimos bien.
• Why: The present-tense stem change does not occur in nosotros. The same applies to vosotros: dormís, not duermís.

Changing every verb that contains o

• Wrong: Tuemo café por la mañana.
• Right: Tomo café por la mañana.
• Why: Stem change is a property of particular verbs, not a spelling rule for every o. Dictionaries and conjugation references normally identify changing verbs.

Using the infinitive’s ending with the changed stem

• Wrong: Ella vuelver mañana.
• Right: Ella vuelve mañana.
• Why: A conjugated verb needs a person ending. For ella, remove -er, change volv- to vuelv-, and add -e.

Copying the change into an ordinary infinitive

• Wrong: Quiero duermer.
• Right: Quiero dormir.
• Why: After a conjugated verb such as querer, the second verb remains an infinitive. Its dictionary form is dormir, not duermir.

Confusing the meanings of contar

• Misleading: translating Cuento una historia as “I count a story.”
• Right: Cuento una historia means “I tell a story.”
• Why: Contar can mean both “to count” and “to tell”; the surrounding noun determines the meaning.

Usage Notes

The pattern is standard across the Spanish-speaking world. The main regional difference in a basic present-tense chart is pronoun choice: Spain commonly uses vosotros/vosotras for informal plural “you,” while most of Latin America uses ustedes. Thus learners focused on Latin American Spanish will hear ustedes vuelven much more often than vosotros volvéis.

In areas that use voseo, singular informal vos may replace tú. The present form often has final stress and therefore lacks the o→ue change: for example, vos podés and vos volvés in widely used Rioplatense forms. Beginners do not need to produce these forms unless they are learning a variety that uses vos, but recognizing them prevents the mistaken belief that every speaker uses tú puedes and tú vuelves.

Several verbs have especially useful constructions. Volver a + infinitive means “to do something again”: Vuelvo a llamar (“I call again”). Soñar con introduces what someone dreams about: Sueño con viajar. Costar commonly agrees with the thing that costs something: El libro cuesta veinte euros but Los libros cuestan veinte euros. These are vocabulary and sentence-pattern facts in addition to the vowel change.

Beyond the Basics / Advanced Use

You do not need to master the following patterns at A1, but they explain forms you will meet later. The simple “boot” rule above is specifically a reliable starting rule for the present indicative; other tenses and moods have their own patterns.

In the present subjunctive (a verb form used in contexts such as wishes, doubt, and requests), -ar and -er verbs generally preserve the familiar distribution: cuente, cuentes, cuente, contemos, contéis, cuenten and vuelva, vuelvas, vuelva, volvamos, volváis, vuelvan. The -ir verb dormir goes one step further: it has ue in the usual changed forms but u in nosotros and vosotros: duerma, duermas, duerma, durmamos, durmáis, duerman.

That o→u pattern also appears in some later forms of -ir verbs. The gerund (the -ing form used with estar) is durmiendo, not dormiendo. In the preterite, dormir changes only in the third-person forms: durmió and durmieron. By contrast, volver and contar do not carry their present stem change into the regular preterite forms volvió and contó.

Commands can also display the changed stem: Duerme bien (“Sleep well”), Vuelve pronto (“Come back soon”), and Cuéntame la verdad (“Tell me the truth”). The written accent in cuéntame is required after attaching the pronoun me; it is not part of the basic o→ue change.

Finally, related words and prefixed verbs often preserve a base verb’s pattern: devolver follows volver (devuelvo, devolvemos), and demostrar follows mostrar (demuestro, demostramos). This is a helpful clue, but actual usage—not visual resemblance alone—determines whether a verb changes.

Practice Tips

1. Learn three forms together. Put dormir — duermo — dormimos or contar — cuento — contamos on one card. The contrast makes the unchanged nosotros form hard to forget.
2. Mark the boot before adding vocabulary. Draw a six-cell present-tense chart, highlight the four changing cells, and conjugate one -ar, one -er, and one -ir verb. Say each form aloud so you hear the contrast between VUEL-vo and vol-VE-mos.
3. Build short personal pairs. Write one sentence about yourself and one about a group: Duermo siete horas; dormimos con la ventana abierta. Meaningful contrasts are more memorable than isolated lists.

Related Concepts

• Prerequisite: Regular -AR Verbs — review how stems and present-tense person endings combine before adding a vowel change.