e → ie
pensar → piensa (él) · pensamos (nosotros)
Spanish 101 · Grammar
Stem-changing verbs
The vowel in the stressed syllable “breaks” in some forms but not others — nosotros is often the giveaway.
The rule
In many e→ie verbs (pensar, entender, querer), the change appears in stressed syllables of the singular persons and third-person plural: piensa, piensan; nosotros pensamos (no stem change).
e→i verbs like pedir, servir, repetir use pido but pedimos — the i appears in the “short” third-person slots in present.
o→ue verbs (dormir, poder, volver) follow the same stress logic: duermo, duermen; dormimos.
Stem change is about the syllable that carries stress in those forms — not about meaning by itself.
¿Puedes ayudarme con la tarea?Can you help me with the homework?
Pedimos la cuenta; ellos piden más tiempo.We ask for the bill; they ask for more time.
Examples in context
Estudio español todos los días.I study Spanish every day.present habit
¿Puedes ayudarme con la tarea?Can you help me with the homework?request
Voy a la biblioteca después de clase.I go to the library after class.movement
No entiendo esta palabra.I do not understand this word.negation
Me gusta la música latina.I like Latin music.gustar
Tenemos clase mañana a las nueve.We have class tomorrow at nine.tener + noun
¿Dónde está el aula?Where is the classroom?estar — location
Es un examen difícil.It is a difficult exam.ser — description
Quick reference
e → i
pedir → pide · pedimos
o → ue
poder → puede · podemos
Common mistakes
Wrong agreement
❌ Wrong: La problema es fácil.
✅ Correct: El problema es fácil.
Problema is masculine despite ending in -a.
Double subjects
❌ Wrong: Yo soy yo estudiante.
✅ Correct: Soy estudiante.
Drop redundant subject pronouns when the verb ending is clear.
Negation placement
❌ Wrong: Entiendo no.
✅ Correct: No entiendo.
Place no immediately before the conjugated verb.
Literal word order
❌ Wrong: ¿Qué hora es qué?
✅ Correct: ¿Qué hora es?
Keep standard question frames; do not copy English order.
Practice questions
Test what you just learned. Select an answer to see instant feedback.
Yo _____ (pensar) en el examen todo el día.
Ella _____ (querer) café, no té.
Nosotros _____ (entender) la explicación.
¿Tú _____ (poder) ayudarme?
Ellos _____ (dormir) ocho horas.
You got 0/5 correct.
Want more practice on Stem-changing verbs?
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Start practicing free →FAQ
How do I know if a verb is stem-changing?
Your vocabulary list or textbook marks e→ie, o→ue, e→i, etc. Changes usually appear in the boot shape of present indicative (not nosotros/nosotras in many -ar/-er verbs). There is no single rule from the infinitive alone—you learn per verb or family.
Why is the yo form sometimes irregular while tú looks regular?
Verbs like hacer (hago) or salir (salgo) add supporting letters or change stems only for yo in the present. The rest of the singular/plural pattern may follow the regular endings. Drill yo alongside ellos because those forms are the most exam-visible.
What is ir a + infinitive?
It is a common periphrasis for near future: Voy a estudiar = I am going to study. Conjugate ir, keep a, and add the unchanged infinitive. It is not the same as the simple future tense learned later.
When can I use the present progressive?
Estar + gerund stresses that an action is in progress right now: Estoy leyendo. Spanish does not use it for stative verbs the way English might (*Estoy queriendo is odd). Follow your book’s list of verbs that prefer simple present.
How do reflexive pronouns line up?
They match the subject: me, te, se, nos, os, se. They usually come before a conjugated verb or attach to an infinitive/command: Me lavo las manos; Voy a lavarme. Placement rules parallel other object pronouns.