Preterit Tense: STEM CHANGING verbs

Do you stem-change verbs in the preterit that end in AR and ER? Yes or no. 

Can we stem-change from e-ie  and from o-ue in the preterit?

• Yes

• No

So....which subject pronouns stem-change? 

He slept and you slept. 

• El duermió y tú duermiste.

• El durmió y tú dormiste.

• El dormió y tú durmiste.

Are you going to stem-change the preterit of PREFERIR in the USTED form? Yes or no?

What THREE things can you say to summarize what he said about stem-change verbs in the preterit? Mention the THREE things. 

So how do you know if they are stem-changers or not?