1. Conjugate stem changers in the preterite tense

2. Stem changing infinitives
Stem changing infinitives are named for what they do– change in the stem.
You are going to make some alteration of the stem before adding the verb endings.
You will use the preterite endings you already know.
The hardest part of stem changers is knowing which ones change and which ones don’t.

3. Two Rules for identifying Preterite Stem-Changers:
1. The infinitive must be a stem-changer in the present tense.
2. The infinitive must end in –ir.

4. Stem changers
There are 2 different ways a stem changing infinitive can change (2 categories).
-The first is ou.
-This includes present tense oue.

5. dormir = to sleep This is a stem changer in the preterite.
First separate the stem from the infinitive ending.
Dorm- is the stem.
Make the stem change ou
New stem durm-
Put into box–
In the present tense, it looks like a boot.
In the preterite tense, it looks like a sandal.
Only the 3rd and 6th box make stem changes.

6. dormir = to sleep
dormí

7. dormir = to sleep
dormí
dormiste

8. dormir = to sleep
dormí
dormiste
durmió

9. dormir = to sleep
dormí
dormimos
dormiste
durmió

10. dormir = to sleep
dormí
dormimos
dormiste
dormisteis
durmió

11. dormir = to sleep
dormí
dormimos
dormiste
dormisteis
durmió
durmieron

12. Stem changers The second category is ei.
(This includes present tense changes eie and ei).
preferir = to prefer is a stem changer.
It is the same steps as dormir.
*When there is more than one vowel that could possible make the change, choose the vowel closest to the verb ending.

13. Preferir = to prefer
First separate the stem from the infinitive ending.
prefer- is the stem.
Make the stem change ei
New stem prefir-
Put into box– remember it will look like a sandal in the preterite. It will only change in the 3rd and 6th boxes.

14. preferir = to prefer
preferí

15. preferir = to prefer
preferí
preferiste

16. preferir = to prefer
preferí
preferiste
prefirió

17. preferir = to prefer
preferí
preferimos
preferiste
prefirió

18. preferir = to prefer preferí preferimos preferiste preferisteis
prefirió

19. preferir = to prefer preferí preferimos preferiste preferisteis
prefirió
prefirieron

20. Stem changers Servir = to serve is a stem changer.
It is the same steps as preferir.

21. servir = to serve First separate the stem from the infinitive ending.
serv- is the stem.
Make the stem change ei
New stem sirv-
Put into box– remember it will look like a sandal. In the preterite, only the 3rd and 6th boxes show change.

22. servir = to serve
serví

23. servir = to serve
serví
serviste

24. servir = to serve
serví
serviste
sirvió

25. servir = to serve
serví
servimos
serviste
sirvió

26. servir = to serve
serví
servimos
serviste
servisteis
sirvió

27. servir = to serve
serví
servimos
serviste
servisteis
sirvió
sirvieron

28. Try these in your notes. Ellos pedir Ella repetir Nosotros sentir
Usted entender
Tú dormir
Ellos pidieron
Ella repitió
Nosotros sentimos
Usted entendió
Tú dormiste