Overview
Some Spanish verbs have different meanings depending on whether they are perfective or imperfective.
Perfective is just a fancy way of saying that a verb describes an action that is considered complete at or by a certain time. Put another way, the perfective aspect is used in tenses that describe singular events that occur (initiate and/or terminate) at the temporal reference point in the sentence. These tenses include the preterite tense and all perfect tenses.
Imperfective is just an equally fancy way of saying that a verb describes an action that is considered incomplete or ongoing in the time referenced in the sentence. Tenses in the imperfective aspect describe events that are ongoing or habitual in relation to the temporal reference point. These tenses include the simple present tense, the imperfect tense, progressive tenses, the conditional tense, and the future tense.
When it comes down to it, the inherent meaning of the verb (from the perspective of a Spanish speaker) does not change with a change in aspect. Instead what is effected is the durative nature of the event being described. This difference comes up a lot when looking at differences between the preterite and and imperfect tenses. Let's take a look!
Change of Pace
Here is a list of verbs that change meaning according to the perfective/imperfective relationship described above.
Verbs that Change
Infinitive Imperfective Translation Perfective Translation
conocer
to know to meet
estar
to become/to get to be
poder
to be able to to manage
querer
to want to try
no querer
to not want to to refuse
saber
to know to find out
tener
to have to receive
Now, let's take a closer look at examples of a few of the above verbs in the different tenses mentioned earlier.
Saber
Aspect Tense Spanish English
Imperfective Simple Present
Sabe la verdad.
I know the truth.
Imperfective Imperfect
Sabía la verdad.
I knew the truth.
Perfective Preterite
Supe la verdad.
I found out the truth.
Perfective Present Perfect
He sabido la verdad.
I have found out the truth.
Tener
Aspect Tense Spanish English
Imperfective Simple Present
Tiene una carta.
He has a letter.
Imperfective Imperfect
Tenía una carta.
He had a letter.
Perfective Preterite
Tuvo una carta.
He received a letter.
Perfective Present Perfect
Ha tenido una carta.
He has received a letter.
Querer
Aspect Tense Spanish English
Imperfective Simple Present
No quieres la invitación.
You don't want the invitation.
Imperfective Imperfect
No querías la invitación.
You didn’t want the invitation.
Perfective Preterite
No quisiste la invitación.
You refused the invitation.
Perfective Present Perfect
No has querido la invitación.
You have refused the invitation.
Poder
Aspect Tense Spanish English
Imperfective Simple Present
Pueden hacerlo.
They are able to do it.
Imperfective Imperfect
Podían hacerlo.
They were able to do it.
Perfective Preterite
Pudieron hacerlo.
They managed to do it.
Perfective Present Perfect
Han podido hacerlo.
They have managed to do it.
Remember that the meanings of the verbs above don't really change. What's going on is that an action in the perfective aspect is viewed as a single event or completed action, wheras an action in the imperfective aspect is considered ongoing.
