Spanish Grammar (See webpage for complete content) Libro digital Herramientas de español Spanish Tools Online Grammar Book 18. Stem-Changing Verbs / Verbos que cambian de raíz All Spanish verbs have a stem (la raíz ) and an ending ( -ar, -er, -ir ): pen sar, volv er, ped ir . There is a large group of verbs that change their stem in the present tense when the stem vowel is stressed. There are three types: those that change -e to -ie- , those that change -o- to -ue- and those that change -e- to -i- : 0 1 2 to think: to come back: to ask (for): pensar (ie) pienso piensas piensa pensamos pensáis piensan volver (ue) vuelvo vuelves vuelve volvemos volvéis vuelven pedir (i) pido pides pide pedimos pedís piden Common verbs following these patterns in the present tense: e > ie: cerrar, comenzar, empezar, entender, pensar, perder, preferir, querer, sentir e > i: elegir, (im)pedir, seguir, servir, (son)reír o > ue: contar, dormir, encontrar, morir, mostrar, poder, resolver, volar, volver Jugar has a different stem change, from u to ue in the same places: juego, juegas, juega, jugamos, jugáis, juegan . Note : All -ir stem-changing verbs change their stems in other tenses (see appendix A ). CC licensed content, Shared previously Provided by : Bowdoin. Located at : http://www.bowdoin.edu/hispanic-studies/tools/newgr/ats/18.htm . License : CC BY-NC-ND: Attribution-NonCommercial-NoDerivatives