Stem Changers
o changes to ue
e changes to ie
e changes to i
All of these make the boot
o changes to ue
In this group all conjugations except nosotros and vosotros change the o in stem to ue:
volar: vuelo ...
mover: muevo ...
dormir: duermo ...
contar, costar, encontrar, recordar, volar
devolver, envolver, morder, mover, volver
dormir, morir
e changes to ie
In this group the e in stem changes to ie for all conjugations except nosotros and vosotros:
empezar: empiezo, ...
entender: entiendo, ...
mentir: miento, ...
cerrar, comenzar, empezar, fregar, negar, pensar
defender, entender, perder, querer
advertir, consentir, hervir, mentir, preferir, sentir
e changes to i
This group changes e in the stem to i, and it applies only to *IR verbs.
pedir: pido, pides, pide, pedimos, -, piden
competir, decir, elegir, gemir, pedir, reír, repetir, servir