Gramática 25: Preterite of -IR verbs that stem change in the present tense

Your textbook is frustrating at times (and this is one of them). Instead of just focusing on the preterite of -IR verbs with present-tense stem changes, it instead insists on talking about the preterite of all families of verbs that stem change in the present tense.

• This is a waste of time.
• As we have already seen, -AR verbs that stem change in the present tense and -ER verbs that stem change in the present tense do not ever show stem changes in the preterite.
• Period.
• No more needs to be said.

But let's repeat it one more time:

• 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.
 

Here's the good news:

• 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 only (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.