Preterite of -IR verbs that stem change in the present tense

Before we go into what these -IR verbs that stem-change in the present tense do in the preterite, let's quickly review what happens to -AR and -ER verbs with present-tense stem changes:

• It doesn't matter if -AR and -ER verbs stem change in the present tense.
   
• They will not show a stem change in the preterite.

For -IR verbs, though, it does matter if they stem change in the present tense.

Let me give you the good news first:

• Most of the time, -IR verbs with present-tense stem changes act as you'd expect them to in the preterite.
   
• When the subject is yo, tú or nosotros, nothing happens to the stem at all. Seriously, not a thing:

However...

When the subject is 3rd-person (whether 3rd-person singular or 3rd-person plural):

• There will be a SIMPLIFIED, single-vowel preterite stem change.
• If the verb stem-changes o-ue in the present, it will make an o to u stem change in the preterite.
• If the verb stem-changes e-ie or e-i in the present, it will make an e to i stem change in the preterite.

Let's look at this all together.

Remember:

• When the subject is yo, tú or nosotros, nothing happens to the stem at all.
• We only make a simplified preterite stem change when the subject is 3rd-person singular or 3rd-person plural.

I hope this helps you to better understand this grammar concept, especially since I won't be focusing on it during Grammar Deep Dive sessions for Unidad 10 (we have bigger grammar fish to fry from Gramática I in this unit).

However, the preterite of -IR verbs that stem change in the present tense is important, and it is featured in your Unidad 10 Examen Cumulativo.