Sometimes the difference in meanings between the two past tenses is such that native English speakers may use different verbs to translate the same Spanish verb, depending on which tense is used. This article focuses on the most common of such verbs.
First, a quick review: The preterite tense (sometimes called the preterit tense) generally is used to describe an event that happened at a specific point in time and was completed; the imperfect is used in telling of events that happened continually, habitually or over an indefinite period of time. Thus, to use the examples at the beginning of this article, fui a tu casa indicates that the speaker went to the house at a specific point in time (say, 4 p.m. last Tuesday). On the other hand iba a tu casa might be used to say "I used to go to your house, "I would go to your house" (when referring to the past) or "I went to your house" (as a matter of custom or habit).
An example of a verb that might be translated differently depending on which of the two tenses is used is conocer, which means "to meet" (that is, meeting someone for the first time) or "to know" (as in knowing a person). In some tenses, the meaning can be ambiguous; quiero conocerla can mean either "I want to meet her" or "I want to know her," depending on the context. But in the preterite and imperfect tenses, that ambiguity disappears.
If you think about how the two tenses are used, the reason for that lack of ambiguity disappears. To know somebody isn't an event that happens and ends at a specific time, but meeting someone is. Thus we use la conocí (preterite) to mean "I met her" and la conocía (imperfect) to mean "I knew her."
But the difference between the two tenses isn't always so intuitive. Here are a handful of other verbs where a distinction of meaning is made between the two tenses:
deber (to be obligated):
- Preterite: Expresses the idea that something should have occurred. Luis debió salir. (Luis should have left.) In some contexts, deber or deber de in the preterite can also indicate a very strong likelihood. Example: Juan debió de salir or Juan debió salir (John must have left).
- Imperfect: Expresses the idea that something should occur. Luis debía salir. (Luis should leave.)
- Preterite: Usually means "managed to" or "was able to." Pudo salvar el gato. (He was able to save the cat.) No pudo salvar el gato. (He couldn't save the cat.)
- Imperfect: Often used to mean "could" to refer to what might happen in the present. ¿Podías ayudarme? (Could you help me?)
querer (to want):
- Preterite: In the affirmative form, can express (but doesn't always) the idea that someone tried or wanted to do something but didn't; in negative form, it usually means "refused." Quise comer un taco. (I wanted to eat a taco, but didn't.) No quise comer un taco. (I refused to eat a taco.) The preterite of querer also can indicate the person wanted to do something and did. Thus, in some contexts, quise comer un taco could mean "I wanted to eat a taco, and I did." Generally, the imperfect form of querer is less ambiguous for indicating that someone wanted to do something.
- Imperfect: Expresses the idea that a person wanted to do something without indicating whether the person did it or not. Quería comer un taco. (I wanted to eat a taco.) No quería comer un taco. (I didn't want to eat a taco.) Note that out of context, neither sentence indicates whether the speaker actually ate a taco.
- Preterite: Found out. Supe la verdad. (I found out the truth.)
- Imperfect: Knew. Sabía la verdad. (I knew the truth.)
- Preterite: Obtained, got. Tuve el regalo. (I received the gift.)
- Imperfect: had, possessed. Tenía el regalo. (I had the gift.)