In the beginning of this unit you learned that the imperfect is used for past actions in progress and the preterit is used for past completed actions. The same distinction can be applied to emotions, mental states and similar conditions:

1. Verbs that describe a mental or physical state are called non-action verbs. These change meaning when you use them in the preterit or imperfect. For example, the verb estar in the preterit means “became” or “got”, whereas in the imperfect it means “was”.
2. The stem-changing verb sentirse means “to feel”, and you can use the imperfect to describe an ongoing feeling, or the preterit to describe the onset or a completed feeling.
3. Reflexive verbs that portray emotions similarly use the imperfect and the preterit to distinguish between *being* in a condition in the past and *becoming* in a condition in the past. Here are a few of the ones you learned in the chapter on reflexive verbs: aburrirse (to become bored); alegrarse (to become happy); enojarse (to become angry); frustrarse (to become frustrated); sorprenderse (to be surprised)
4. Another irregular verb that expresses a change of emotion in the preterit is ponerse (to become); in the imperfect it expresses a continuous or habitual emotional state.
5. Also, as you learned in Spanish 1, don’t forget the expressions with “tener” that show physical states and emotions: tener hambre (to be hungry), tener sed (to be thirsty), tener frío (to be cold), tener calor (to be hot), tener suerte (to be lucky).

Understanding the subtle differences between these two tenses will help you understand that non-action verbs change meaning when used in the imperfect or the preterit.