whats the difference between stem changing in the present tense and the preterite
I'll send this to our Spanish expert, SraJMcGin.
-ar and -er verbs that change their stem in the present tense do not change in the preterite. They are conjugated just like other regular preterite verbs, using the regular endings.
cerrar
cerré
cerraste
cerró
cerramos
cerrasteis
cerraron
entender
entendí
entendiste
entendió
entendimos
entendisteis
entendieron
-ir verbs that change their stem in the present tense do change in the preterite, but in a different way. They change e:i and o:u in the third person, singular and plural.
preferir
preferí
preferiste
prefirió
preferimos
preferisteis
prefirieron
dormir
dormí
dormiste
durmió
dormimos
dormisteis
durmieron
Note that stem-changing verbs in the Present Tense can be -ar, -er, or -ir but in the Preterit, only -ir verbs. There ARE, however, irregular verbs in the Preterit, but that's not the same as "stem-changing" verbs.
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Sra
The difference between stem-changing verbs in the present tense and the preterite tense lies in the way the verb stems change.
In the present tense, stem-changing verbs (also known as shoe verbs) exhibit a vowel change in the stem of the verb for certain pronouns. These changes occur in all forms of the present tense except for nosotros and vosotros. For example, the verb "pensar" (to think) changes its stem from "e" to "ie" for all pronouns except nosotros/vosotros, resulting in conjugations like "pienso" (I think), "piensas" (you think), and so on.
On the other hand, in the preterite tense, stem-changing verbs (also known as radical-changing verbs or boot verbs) undergo a vowel change in the stem for certain pronouns, but this change only occurs in the third person singular and plural forms. These changes typically involve an "e" to "i" or "o" to "u" switch in the stem of the verb. For example, the verb "pedir" (to ask, to order) changes its stem from "e" to "i" in the third person singular and plural, resulting in conjugations like "pidió" (he/she/it asked) and "pidieron" (they asked).
To determine whether a verb is stem-changing in the present tense or the preterite tense, you would need to consult a list of stem-changing verbs or identify the specific pattern of vowel changes associated with each tense.
To get a complete understanding of stem-changing verbs and their conjugations, it's helpful to study verb charts and practice conjugating them in both the present and preterite tenses. You can find comprehensive lists of stem-changing verbs and their conjugations in Spanish language textbooks, online resources, or language learning apps.