• How it works
• E changes to IE
• O changes to UE
• Stem-changing verbs in the preterite (pretérito perfecto)

How it works

In the present tense, some verbs have a stem change: a letter in its root changes in some grammatical persons. There are two types of stem changes:

E changes to IE

Here is pensar (to think), in the present tense:

yo pienso

tú piensas

él / ella / usted piensa

nosotros / nosotras pensamos

(vosotros / vosotras pensáis)

ellos / ellas / ustedes piensan

This happens in many verbs; it doesn't matter if they are -ar, -er or -ir. Note that the E changes to IE in every person except nosotros and vosotros.

Here are some common “E to IE” verbs:

cerrar - to close

divertirse - to have fun

empezar* - to start / to begin

entender* - to understand

mentir - to lie

pensar - to think

perder - to lose

preferir* - to prefer

querer - to want / to love

recomendar - to recommend

sentarse - to sit down

sentirse - to feel

*The stem change always happens in the strong syllable: empiezo, entiendo, prefiero.

O changes to UE

Here is soñar (to dream), in the present tense:

yo sueño

tú sueñas

él / ella / usted sueña

nosotros / nosotras soñamos

(vosotros / vosotras soñáis)

ellos / ellas / ustedes sueñan

Again, the O changes to UE in every person except nosotros and vosotros.

Here are some common “O to UE” verbs:

acostarse - to go to bed / to lie down

almorzar - to have lunch

contar - to tell / to count

costar - to cost

devolver - to return (an item)

dormir - to sleep

dormirse - to fall asleep

encontrar - to find

mover - to move (an item)

morir - to die

poder - to be able to

recordar - to remember

sonar - to sound

soñar - to dream

volar - to fly

volver - to return

Stem-changing verbs in the preterite (pretérito perfecto)

Stem-changing verbs do not change their stem in the pretérito perfecto.

Here is pensar (to think), in the pretérito perfecto tense. As you can see, it is 100% regular.

yo pensé

tú pensaste

él / ella / usted pensó

nosotros / nosotras pensamos

(vosotros / vosotras pensasteis)

ellos / ellas / ustedes pensaron

Here is soñar (to dream), in the pretérito perfecto tense. Again, 100% regular.

yo soñé

tú soñaste

él / ella / usted soñó

nosotros / nosotras soñamos

(vosotros / vosotras soñasteis)

ellos / ellas / ustedes soñaron

Verbs divertirse, mentir, morir, preferir, querer, sentirse, dormir and poder are irregular in the pretérito perfecto tense. Try to look up their conjugations and memorize them.