Conjugating the pretérito: Stem-changing verbs

Verbs which are stem-changing in the present tense may or may not be in the pretérito. Note that they use the same endings for the pretérito as regular verbs.

Stem-changing verbs that end in -AR and -ER do not stem-change in the pretérito.

Stem-changing verbs that end in -IR have a different stem change in the pretérito. Those that have an E change to an I, and those that have an O change to a U, but only in the third person conjugations.

Verbs which end in -CAR, -GAR, and -ZAR have a  stem-change in the first person singular of the pretérito, even if they are not stem-changing in the present tense.

In these verbs, the C, G, or Z changes to QU, GU, or C, respectively. (Why is this?)

Note that since -AR verbs lose their stem-change, -CAR, -GAR, and -ZAR verbs which are stem-changing in the present (e.g., comenzar) lose that stem-change but gain a new one in the pretérito: yo comienzo (present) --» yo comencé (pretérito).

©   Laura K. Lawless
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