Stem changing verbs are verbs where the vowel in the stem changes in certain conjugations. Stem changing verb rules are mostly general and each verb must usually just be individually memorized as some change in differing tenses.

Types of Stem Changes

There are three main types of stem changes:

1. e > ie (e.g., Pensar, Querer)
2. e > i (e.g., Pedir, Servir)
3. o > ue (e.g., Dormir, Poder)

General Conjugation Pattern

1. Remove the verb ending (-ar, -er, or -ir) to get the stem
2. Apply the appropriate stem change for all conjugations except nosotros and vosotros
3. Add the appropriate ending