Preterite of -ir Stem Changers
By: Laurence Fairchild and Jose Mejia
Stem-changing -IR verbs
Verbs with an e-ie, e-i, or o-u in the present keep the e or o of the infinitive in preterit conjugations except for 3rd person singular and plural where they change: e-i and o-u in the 3rd person.
Reír and sonreír also fall into this category even though the ending is ír. Here are some examples.