Preterite and Imperfect Past Tense
What are the differences
and how do you use them?

On top of having a simple present and future tense, Spanish has two simple past tenses: preterite and imperfect. The word "simple" means that they are the basic past tenses, not that they are necessarily easy to understand. They are simple in that they don't have helping verbs to create them.

The two tenses, preterite and imperfect, have different meanings and are not interchangeable. A good way to think about them is this:

Imperfect: The background for the story. The process.
Preterite: The events of the story. The result.

Imperfect

The imperfect tense is expressed by flexible, unlimited time. It shows the transition, or development of events in the past, but not the event itself. The imperfect shows the background information that surrounds the events (the events being the preterite tense verbs).

1. Tells what was happening at a certain time.

Se inclinaba sobre el mural cuando... He was leaning over the wall when...
Reían de ti. They were laughing at you.

2. Tells what used to happen over a period of time.

Cuando vivíamos en México... When we lived in Mexico...
Cuando comían la cena... When they ate supper...*

*This is understood to mean: "when they ate supper each night as a regular course of action."

3. Describes a mental, emotional or physical state in the past.

El no sabía quien era ella. He didn't know who she was.
Todos le amaban. Everybody loved him.

4. Tells time in the past and sets the background for other events to occur.

Eran las diez. It was 10 o'clock.
No había ningún gato. There weren't any cats.

Preterite

This is the past tense that is characterized by definitive action. It is limited and expresses a completed action-an event in the past.

1. The normal form of the verb tense that would be a one-time action, or a specific occurrence of the event.

Fuimos al cine. We went to the theater.
El dormió bien. He slept well.
Comieron la cena. They ate supper.*

*This is understood to mean: "they ate supper at a specific, one-time event."

2. Depending on the mental and emotional state being conveyed the preterite expresses a different meaning than the imperfect.

Imperfect:
No quería pelear. He didn't want to fight.

Preterite:
No quiso pelear. He refused to fight.

There are many examples of this, but this is just to show that the two tenses, preterite and imperfect, do not carry the same meaning.

Working Together

The imperfect and preterite past tense verbs are often found together in the same sentence or story. This is best seen when thinking through an event.

"I rode [imperfect] a green bike to school every day in 5th grade. One day I was getting on [imperfect because it is background information, not the event] my bike when Bill ran into [preterite] me."

Conjugating Imperfect and Preterite

Imperfect

-ar verbs (hablar) -er/-ir verbs (comer/vivir)
yo -aba (hablaba) -ía (comía/vivía
tú -abas (hablabas) -ías (comías/vivías)
él -aba (hablaba) -ía (comía/vivía)
nosotros -ábamos (hablábamos) -íamos (comíamos/vivíamos)
vosotros -abais (hablabais) -íais (comíais/vivíais)
ellos -aban (hablaban) -ían (comían/vivían)

Preterite

-ar verbs (hablar) -er verbs (comer) -ir verbs (vivir)
yo -é (hablé) -í (comí) -í (viví)
tú -aste (hablaste) -iste (comiste) -iste (viviste)
él -ó (habló) -ió (comió) -ió (vivió)
nosotros -amos (hablamos) -imos (comimos) -imos (vivimos)
vosotros -asteis (hablasteis) -isteis (comisteis) -isteis (vivisteis)
ellos -aron (hablaron) -ieron (comieron) -ieron (vivieron)

While these two tenses can give the new student of Spanish some difficulty, this summary should help you see the difference and start to learn the subtle meaning of each.

Technicality: It is not technically accurate to call the imperfect a "tense." It is the past tense with an imperfect aspect. In English this is properly called a "past imperfective." However, in practice, since we conjugate the past imperfective like we do any other verb, it is easiest to think of it as a tense. Anyone who knows the difference and really cares, probably isn't reading this anyway.