1. Preterite of –IR Stem Changers

2. Common –IR Stem Changers
Preferir (to prefer)
Mentir (to lie)
Sentirse (to feel)
Divertirse (to enjoy yourself) (also a reflexive)
Pedir (to ask for)
Repetir (to repeat)
Vestirse (to get dressed)
Competir (to compete)
Servir (to serve)
*Sonreír (to smile)
Dormir (to sleep)
Morir (to die)
* Sonreír has irregular forms—Sonreí, Sonreíste, Sonrió, Sonreímos, Sonreísteis, Sonrieron
-IR Endings in the Preterite
Í imos
iste isteis
ió ieron
-AR and –ER stem changers do not change in the preterite

3. To Conjugate
Conjugate the yo, tú, nosotros and vosotros forms regularly.
Preferir Dormir
preferí preferimos dormí dormimos
preferiste preferisteis dormiste dormisteis

4. To Conjugate
In the él/ella/usted and ellos/ellas/ustedes form, the E or O that usually changes STILL changes. The E will change to an I (for both e-i and e-ie) and the O will change to a U (for o-ue).
Preferir Dormir
preferí preferimos dormí dormimos
preferiste preferisteis dormiste dormisteis
prefirió prefirieron durmió durmieron