Stem-changing verbs are a distinctive class of verb, some of whose forms are irregular in a patterned, predictable way. Here's how they work:
- The stem of a verb is its infinitive minus -ar, -er, -ir.
- EG: pens|ar, entend|er, prefer|ir, dorm|ir
- The changes occur in some verbs whose final stem-vowel is e or o. (in rare cases u or i). Some verbs meeting this definition do not change.
Examples:
- defender has changes, ofender does not
- contar has changes, montar does not
- In some of the verb's forms, this stem-vowel changes to another vowel or to a pair of vowels: e changes to ie or to i, o changes to ue or to u.
- This occurs in patterns, rather than randomly.
- Not all tenses are affected, and in most cases not all forms of the affected tenses have changes.
- All stem-changing verbs have changes in the present indicative and present subjunctive, and in the imperatives (commands) derived from these.
- Stem-changing -ir verbs have them in the preterite, present participle (gerundio) and imperfect subjunctive as well.
- There are five stem-change patterns; click on links to model verbs:
- -ar and -er verbs with e→ie changes (model)
- -ar and -er verbs with o→ue changes (model)
- -ir verbs with e→ie and e→i changes (model)
- -ir verbs with e→i changes (model)
- -ir verbs with o→ue and o→u changes (model)
- Click here for a printable color document displaying all patterns, with model verbs and lists.
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