Both the preterit and the imperfect are past tenses. They’re actually different ways of looking at the past. Let’s say you’re looking at a single moment in the past—for example, 12:00 yesterday. Mealtime. I can look at the moment and the action of eating in two ways: I ate at 12:00 yesterday. What I actually mean when I say that sentence is that I started eating at 12:00. I was eating at 12:00 yesterday. What that means is that I began at some unspecified point before 12:00 and ended at some unspecified point after 12:00. All you know is that at that moment in time, I was in the process of eating.
The preterit is used when you want to show the beginning or end of an action: Comí a las doce ayer. I ate at 12:00 yesterday. The imperfect is used when you want to show an action in progress: Comía a las doce ayer. I was eating at 12:00 yesterday.
One of these sentences would make you sadder than the other. Which? Mi abuelo se moría. Mi abuelo se murió. You’d rather hear “mi abuelo se moría” because that means “my grandfather was dying.” It doesn’t necessarily mean he died. Maybe he did, but maybe he recovered. “Mi abuelo se murió” means “my grandfather died.”
Which of the following sentences is going to make the teacher mad? Los estudiantes se reían cuando la profesora entró en la clase. Los estudiantes se rieron cuando la profesora entró en la clase. Don’t just click and scroll for the answer. Think about it. The first sentence says, “The students were laughing when the teacher entered the class.” Apparently, someone had told a funny story. The laughing was already going on (in progress) when the teacher entered (beginning/ending of action). The second sentence says, “The students laughed when the teacher entered the class.” Apparently, she was wearing something really strange that made them laugh when they saw her. You see the beginning of the laughter AND the beginning/ending of the teacher’s entrance.
The following sentence has one verb in the preterit and one in the imperfect. One of the verbs shows the beginning of an action (preterit), and the other shows an action in progress (imperfect): He was reading when the phone rang. Leía cuando el teléfono sonó. Imagine that you step up to a window to spy on someone. What you see is someone sitting on his bed reading. You don’t know when the reading started; you just know that it was in progress when you started watching. The window pane was thin, and you heard the phone ring. You saw (heard) the beginning of that action.
There are some verbs that have a special meaning in the preterit: conocer saber tener querer Think about it: what is it if you began to know someone? What is it if you began to know a piece of information? preteritimperfect conocer met knew saber found out knew tener got had querer tried wanted no querer refused didn’t want
Lo supe ayer. I found it out yesterday. Ya lo sabía. I already knew it. Lo conocí ayer. I met him yesterday. Lo conocía cuando era niño. I knew him when he was a child. Tuve la carta ayer. I got the letter yesterday. Ya tenía la carta. I already had the letter. Quise leerlo. I tried to read it. Quería leerlo. I wanted to read it. No quise leerlo. I refused to read it. No quería leerlo. I didn’t want to read it.
The imperfect has another use, besides showing an action in progress. It’s used to show habitual past action. Cuando era niño, jugaba al fútbol. What that sentence means is that when I was a child, I customarily played soccer. I don’t mean just once. It was something I did regularly as a child. You can translate the sentence three ways: When I was a child, I played soccer. When I was a child, I used to play soccer. When I was a child, I would play soccer.
All the verbs in the following paragraph are in the imperfect because all are habitual past actions: En 1955 todos los niños asistían a la escuela. Iban a la iglesia todas las semanas. Llevaban buena ropa. Jugaban con sus amigos, y viajaban a la playa con sus padres en el verano. In 1955 all the children attended school. They went to church with every week. They wore good clothes. They would play with their friends and would travel to the beach with their parents in the summer. However, the minute you put a time limit to a past action, it ceases to be habitual, and you use the preterit: In 1955 all the children attended school one day. En 1955 todos los niños asistieron un día. When I was a child, I played soccer ten times. Cuando era nino, jugué al fútbol diez veces. When you put a time limit on it, you’re showing the end of the action, and that means you need the preterit.