-ir stem-changing verbs in the Preterite -ar and –er verbs that have a stem change in the Present tense do not have a corresponding change in the Preterite. However, -ir shoe verbs do have a stem change in the Preterite tense. Unlike in the Present tense, they do not change in the shoe, they change only in the 3 rd persons (he, she, you (Ud), they and you (Uds) forms. Present tense o>ue changes become o>u in the preterite. Present tense e>ie and e>i changes become e>i in the Preterite.
Dormir (ue, u) PresentPreterite Duermodormimosdormídormimos Duermesdormísdormistedormisteis Duermeduermendurmiódurmieron
Sentir (ie, i) PresentPreterite Sientosentimossentísentimos Sientessentíssentistesentisteis Sientesientensintiósintieron
Pedir (i, i) PresentPreterite Pidopedimospedípedimos Pidespedíspedistepedisteis Pidepidenpidiópidieron