The first conjugation (-ar) and the second conjugation (-er) stem-changing verbs do not have stem changes in the preterit tense. On the other hand, the third conjugation stem-changing verbs do have stem changes that occur in the third person singular and plural.
There are two patterns: o — u, and e — i.
I will illustrate these patterns below. I will indicate where the stem changes with underlined italic type. The endings for m-changing verbs are regular.
When you look up these verbs in a dictionary, you will find in parentheses the following standard notations.
dormir (ue, u) / to sleep
mentir (ie, i) / to lie
servir (i, i) / to serve
Remember that the first vowel(s) mean(s) that there is a stem change in present tense in the form of a shoe The second vowel means that there is also a stem change in the preterit tense in the third person singular and plural, as well as the present participle . We will see examples of all three of these verbs.
Therefore let’s look have do this verbs change in the third conjugation