There is no proper system for the identification of stem-changing verbs when seen in infinitive form. Therefore they have to be learned according to their groups which are three in number. Every Spanish verb that has –AR, -ER or –IR ending has regular ending for present tense conjugation. The difference arises when the stem vowel in all pronouns is changed except in “nosotros” and “nosotras”. In order to know the stem changing verbs the following groups should be learnt.
This group consists of the verbs in which stem vowel is changed from “e” to “ie”
Perder meaning “to lose”
Pensar meaning “to think”
Preferir meaning “to prefer”
If the verb stem has more than one “e” such as “preferir” the change takes place in the stressed “e”. Following are some examples.
Spanish Pronoun e → ie
ellos/ellas piensan pierden prefieren
nosotros/nosotras pensamos perdemos preferimos
usted piensa pierde prefiere
yo pienso pierdo prefiero
él/ella piensa pierde prefiere
tú piensas pierdes prefieres
ustedes piensan pierden prefieren
In this group the stem vowel is converted from “e” to “I”.
pedir meaning “to ask for”
repetir meaning “to repeat”
servir meaning “to serve”
The stem changing verbs of this group end at –IR and are not many.
Examples are given below.
Spanish Pronoun e → i
ellos/ellas piden repiten sirven
él/ella pide repite sirve
ustedes piden repiten sirven
yo pido repito sirvo
usted pide repite sirve
tú pides repites sirves
nosotros/nosotras pedimos repetimos servimos
In The verbs of this group the stem vowel is converted from “o” to “ue”.
Poder meaning “to be able to”
recordar “to remember”
dormir “to sleep”
Following are the examples.
Spanish Pronoun o → ue
ellos tú duermes puedes recuerdas
/ellas duermen pueden recuerdan
nosotros/nosotras dormimos podemos recordamos
yo duermo puedo recuerdo
usted duerme puede recuerda
él/ella duerme puede recuerda
ustedes duermen recuerdan
This exercise as all other requires a lot of practice and patience as well. For a new learner some concepts might be very vague in the beginning but there are certain helping materials which can help the learner.