conjugation.preterite.y-spelling
The y forms: leyó, cayó, construyó
When an unstressed i lands between vowels, it is written y: leer → leyó, leyeron; construir → construyó; gerund leyendo, construyendo.
conjugationA2, B1standardinternally_reviewedv1.0.0
Explanation
Verbs whose stem ends in a vowel (leer, caer, oír, creer) can't write i between vowels in the preterite third person: the -ió/-ieron endings become -yó/-yeron. Leer → leyó, leyeron; oír → oyó, oyeron.
Verbs in -uir do the same and extend the y into the whole present: construyo, construyes... construyó, construyeron; huir → huyó.
The y also appears in the gerund (leyendo, cayendo, construyendo) and the imperfect subjunctive (leyera, construyera). The other preterite persons take a written accent instead: leí, leíste, leímos.
Examples
She read the whole contract.
Region: global
They built the building in two years.
Region: global
I heard a strange noise.
Region: global