Stem-changing verbs: "e → i, e → ie, ..."

Aprender las cuatro reglas principales para entender los cambios de raíz en los verbos.

(Learn the four main rules to understand stem changes in verbs.)

Teacher explanation

Stem-changing verbs in Spanish: what is happening?

Some Spanish verbs change a vowel in the stem when you conjugate them in the present tense.
These are often called “stem-changing verbs” or “boot verbs”.
Example: preferir → prefiero, quieres, duermen, juego.

Two things change at the same time:

1) the ending (-o, -as, -a, -amos, …) like a normal -ar/-er/-ir verb
2) the vowel in the stem (e → ie, e → i, o → ue, u → ue)

Where does the stem change? (the “boot” rule)

The stem changes in these persons:
- yo
- tú
- él / ella / usted
- ellos / ellas / ustedes
The stem does not change in:
- nosotros
- vosotros

A simple way to remember:

Draw a table of the 6 persons.
Mark a boot shape around yo, tú, él/ella, ellos/ellas.
Inside the boot = stem changes.
Outside the boot (nosotros, vosotros) = no change.

The four main stem changes

Type	Infinitive	Example (yo)	Meaning
e → ie	preferir	yo prefiero	I prefer
e → ie	querer	yo quiero	I want
e → ie	entender	yo entiendo	I understand
e → i	pedir	yo pido	I ask for / I request
e → i	servir	yo sirvo	I serve
o → ue	volver	yo vuelvo	I return / I go back
o → ue	soler	yo suelo	I usually …
o → ue	dormir	yo duermo	I sleep
u → ue	jugar	yo juego	I play

How to build a stem-changing form: 3 steps

Find the stem: remove -ar, -er, -ir from the infinitive.
- preferir → stem: prefer-
- dormir → stem: dorm-
Apply the vowel change (if the person is inside the “boot”).
- prefer- → prefier- (e → ie)
- dorm- → duerm- (o → ue)
Add the normal present ending (-o, -es, -e, -emos, -imos, etc.).
- prefier- + -o → prefiero
- duerm- + -en → duermen

Important: the meaning of the verb stays the same. Only the sound and spelling of the stem change.

Compare: with and without stem change

Person	Preferir (e → ie)	Dormir (o → ue)
yo	prefiero	duermo
tú	prefieres	duermes
él / ella	prefiere	duerme
nosotros	preferimos (no change)	dormimos (no change)
vosotros	preferís (no change)	dormís (no change)
ellos / ellas	prefieren	duermen

Notice how nosotros and vosotros are the only forms that keep the original vowel.

Typical “first mistakes” to avoid

Changing the stem where you should not:
- ~~Nosotros prefirimos~~ → Nosotros preferimos
- ~~Vosotros duermís~~ → Vosotros dormís
Forgetting the stem change inside the boot:
- Yo prefero → Yo prefiero
- Ellos dormen → Ellos duermen
Inventing impossible forms:
- ~~entiendemos~~ → entendemos
- ~~pieden~~ → piden

Strategy: when you speak or write, ask yourself quickly:

Is the person inside the boot? → change the stem.
Is it nosotros / vosotros? → keep the stem.

Meaning patterns that help you remember

Many very common verbs about wants and preferences are e → ie:
- querer (to want)
- preferir (to prefer)
- entender (to understand)
Many verbs about physical actions are o → ue:
- dormir (to sleep)
- volver (to return)
- poder (can, to be able to – not in the table, but very common)
e → i is frequent for verbs about asking or serving:
- pedir (to ask for, to order)
- servir (to serve)
jugar (to play a game / sport) is special: u → ue → juego.

Mini check: can you explain this to yourself?

Test yourself with these questions. If you can answer them in your own words, you understand the topic.

For the verb querer, which forms change the stem (add ie) and which do not?
Why is nosotros preferimos correct, but nosotros prefierimos is not?
How do you form ellos duermen starting from dormir? (three steps: stem, change, ending)
What is the difference between pido and pedimos in terms of stem change?

If one answer is not clear, go back to:

the boot rule section, and
the 3 steps to build a form.

What you should be able to do now

Recognize when a verb is stem-changing in the present tense.
Know in which persons the stem changes and in which it does not.
Conjugate and use in context verbs like:
- preferir: prefiero, prefieres, preferimos…
- querer: quiero, quieres, queremos…
- entender: entiendo, entiendes, entendemos…
- pedir: pido, pides, pedimos…
- dormir: duermo, duermes, dormimos…
- jugar: juego, juegas, jugamos…
Pay attention to the difference between forms like quiere / queremos, duermo / dormimos when you speak about yourself, other people, or a group.

With this, you are ready to focus in class on speaking and using these verbs fluently in real conversations.

Some verbs change their stem when conjugated in the present tense, except in nosotros and vosotros.

Cambio de raíz (Stem change)	Verbo (Verb)	Ejemplo (Example)
e → ie	Preferir	Yo prefiero el pan. (I prefer* the bread.)*
	Querer	Yo quiero la vainilla. (I want* the vanilla.)*
	Entender	Tú entiendes la receta. (You understand* the recipe.)*
e → i	Pedir	Él pide el ajo. (He orders / asks for* the garlic.)*
e → i	Servir	Él sirve el chocolate. (He serves* the chocolate.)*
o → ue	Volver	Tú vuelves con los tomates. (You come back* with the tomatoes.)*
	Soler	Yo suelo probar la comida antes de servirla. (I usually* taste the food before serving it.)*
	Dormir	Ellos duermen después de cocinar el arroz. (They sleep* after cooking the rice.)*
u → ue	Jugar	Ellas juegan con la masa. (They play* with the dough.)*

Exercise 1: Multiple choice

Instruction: Choose the correct answer

1. Yo ______ un kilo de tomates y medio kilo de manzanas, por favor.

2. Nosotros no ______ esta lista de la compra; es muy larga.

3. Ellos siempre ______ carne de pollo en el mercado.

4. Por la noche yo ______ pronto porque mañana hago la compra temprano.

Exercise 2: Rewrite the phrases

Instruction: Complete and rewrite the sentences by correctly conjugating the stem-changing verb (in parentheses) in the present indicative.

Show/Hide translation Show/Hide hints

Yo (preferir) trabajar en casa.

⇒ _______________________________________________ Example
Yo prefiero trabajar en casa.
(Yo prefiero trabajar desde casa.)
Tú (querer) un café con leche.

⇒ _______________________________________________ Example
Tú quieres un café con leche.
(Tú quieres un café con leche.)
Él (pedir) la cuenta en el restaurante.

⇒ _______________________________________________ Example
Él pide la cuenta en el restaurante.
(Él pide la cuenta en el restaurante.)
Nosotros (entender) bien la receta de la tortilla.

⇒ _______________________________________________ Example
Nosotros entendemos bien la receta de la tortilla.
(Nosotros entendemos bien la receta de la tortilla.)
Ellos (dormir) una siesta después de comer.

⇒ _______________________________________________ Example
Ellos duermen una siesta después de comer.
(Ellos duermen una siesta después de comer.)
Vosotros (jugar) al fútbol los sábados.

⇒ _______________________________________________ Example
Vosotros jugáis al fútbol los sábados.
(Vosotros jugáis al fútbol los sábados.)

Exercise 3: Grammar in action

Instruction: Talk and decide what you will buy today and what you prefer to leave for tomorrow.

Show/Hide translation

Situation

Dos compañeros de piso organizan la compra semanal en el supermercado.

Discuss

¿Qué frutas y verduras preferís comprar hoy? ¿Por qué? (Which fruits and vegetables would you prefer to buy today? Why?)
En el supermercado, ¿qué soléis comprar primero y qué dejáis para el final? ¿Por qué? (At the supermarket, what do you usually buy first and what do you leave until last? Why?)

Useful words and phrases

Prefiero la fruta y la verdura del mercado. (I prefer fruit and vegetables from the market.)
Normalmente suelo hacer la compra grande el sábado por la mañana. (Usually I do the big shop on Saturday morning.)
Hoy quiero carne, pescado, yogur y galletas, pero no mucho zumo. (Today I want meat, fish, yogurt and biscuits, but not much juice.)

Use in conversation

preferir + comida (preferir + comida)
querer + producto del supermercado (querer + producto del supermercado)
soler + hacer la compra (soler + hacer la compra)