Some -er and -ir verbs have a vowel right before the ending: leer, creer, oír, caer, traer, huir, construir, incluir. In the preterite, their third-person endings -ió and -ieron would crash into that vowel, creating awkward clusters like *leió. Spanish solves this by writing y instead of i in those two forms.
The Change
In the third-person singular and third-person plural:
- -ió becomes -yó
- -ieron becomes -yeron
The rest of the forms keep the regular spelling — but they need written accents on the i to show that it is a separate syllable, not part of a diphthong with the previous vowel.
leer
| Subject | leer |
|---|---|
| yo | leí |
| tú | leíste |
| él / ella / usted | leyó |
| nosotros / nosotras | leímos |
| ellos / ellas / ustedes | leyeron |
Notice the accent on the í in leí, leíste, leímos. Without it, you would end up pronouncing lei as a single syllable (diphthong). The accent tells the reader that the i carries its own syllable.
Ella leyó el artículo ayer.
She read the article yesterday.
Leyeron el informe con atención.
They read the report carefully.
oír
| Subject | oír |
|---|---|
| yo | oí |
| tú | oíste |
| él / ella / usted | oyó |
| nosotros / nosotras | oímos |
| ellos / ellas / ustedes | oyeron |
¿Oyeron el ruido anoche?
Did you (all) hear the noise last night?
Él no oyó la alarma.
He did not hear the alarm.
More Verbs in This Group
| Infinitive | Meaning | 3rd sg. | 3rd pl. |
|---|---|---|---|
| leer | to read | leyó | leyeron |
| creer | to believe | creyó | creyeron |
| oír | to hear | oyó | oyeron |
| caer | to fall | cayó | cayeron |
| huir | to flee | huyó | huyeron |
| construir | to build | construyó | construyeron |
| incluir | to include | incluyó | incluyeron |
| destruir | to destroy | destruyó | destruyeron |
El arquitecto construyó una casa moderna.
The architect built a modern house.
El informe incluyó muchos detalles.
The report included many details.
Verbs in -uir
Verbs ending in -uir (huir, construir, incluir, destruir, contribuir) do the same thing, even though their spelling looks a bit different. The i between u and the ending becomes y. Importantly, these verbs do not take the accent on huí, huiste, huimos, because the combination ui is naturally treated as a diphthong in Spanish spelling.
| Subject | construir |
|---|---|
| yo | construí |
| tú | construiste |
| él / ella / usted | construyó |
| nosotros / nosotras | construimos |
| ellos / ellas / ustedes | construyeron |
Why the Accents Matter
The accents in leí, leíste, leímos are not decorative. In Spanish, ei and ai normally form diphthongs (one syllable, as in rey). Writing leí with an accent tells readers that here the i breaks away from the e and forms its own syllable: le-í, two syllables.
Common mistakes
❌ Ella leió el libro ayer.
Wrong: the unstressed i between two vowels must become y.
✅ Ella leyó el libro ayer.
Correct: leyó — i becomes y between vowels.
❌ Ellos caieron en la nieve.
Wrong: same rule — the i becomes y in the third person.
✅ Ellos cayeron en la nieve.
Correct: cayeron with y.
❌ Yo lei una novela la semana pasada.
Wrong: missing the accent on the í to break the diphthong.
✅ Yo leí una novela la semana pasada.
Correct: leí with an accent separates the two syllables.
❌ Él construió una casa moderna.
Wrong: -uir verbs also change i to y in the third person.
✅ Él construyó una casa moderna.
Correct: construyó with y.
Related Topics
- Regular -er and -ir VerbsA2 — Regular -er and -ir verbs share one set of preterite endings: -í, -iste, -ió, -imos, -ieron.
- Spelling: -car, -gar, -zarA2 — Verbs ending in -car, -gar, and -zar change spelling in the yo form of the preterite to preserve their sound.
- Irregular GerundsA2 — Stem-changing -ir verbs and verbs with a vowel before the ending form special gerunds like durmiendo, pidiendo, and leyendo.