Spanish - The Preterite Tense

To form the preterite, drop the 'ar' from the infinitive and add:

• é
• aste
• ó
• amos
• asteis
• aron

For 'ir'/'er' verbs, drop the ending and add:

• í
• iste
• ió
• imos
• isteis
• ieron

http://www.studyspanish.com/lessons/pretimp1.htm

Use of the preterite tense implies that the past action had a definite beginning and definite end:

• Juan habló de la una hasta las dos. 

Juan spoke from one until two o'clock.

(clearly stated beginning and end)

It is important to realize that the beginning and the end may not always be clearly stated:

• Juan habló dos horas.

Juan spoke for two hours.

• Juan habló con la estudiante.

Juan spoke with the student.
(both have an implied beginning and end)

The preterite is used for actions that can be viewed as single events:

• Ella caminó por el parque.

She walked through the park.

• Ellos llegaron a las ocho.

They arrived at eight o'clock.

The preterite is used for actions that were repeated a specific number of times, or occurred during a specific period of time:

• Ayer escribí tres cartas.

Yesterday I wrote three letters.

• Vivimos allí por cuatro años.

We lived there for four years.

The preterite is used for actions that were part of a chain of events:

• Ella se levantó, se vistió, y salió de la casa.

She got up, dressed, and left the house.

The preterite is used to state the beginning or the end of an action:

• Empezó a nevar a las ocho de la mañana.

It began to snow at eight in the morning.

N.B:- The preterite tells us specifically when an action took place

'ar' and 'er' verbs that change their stem in the present tense do not change in the preterite. They are conjugated just like other regular preterite verbs:

Entender:

• entendí
• entendiste
• entendió
• entendimos
• entendisteis
• entendieron

Cerrar:

• cerré
• cerraste
• cerró
• cerramos
• cerristeis
• cerraron

'ir' verbs that change their stem in the present tense do change in the preterite, but in a different way. They change e:i and o:u in the third person, singular and plural:

Preferir:

• preferí
• preferiste
• prefirió
• preferimos
• preferisteis
• prefirieron

In order to preserve the sound of the infinitive, a number of verbs change orthographically (spelling) in the preterite tense. The following changes occur in the "yo" form only:

• Verbs that end in -gar change g to gu
• Verbs that end in -car change c to qu
• Verbs that end in -zar change z to c

Here are three examples:

• yo jugué (jugar) 
• yo busqué (buscar)
• yo almorcé (almorzar)

For verbs that end in 'aer', 'eer', 'oír', and 'oer', the él/ella/usted forms use the ending "yó" (rather than ió) and the third person plural uses the ending "yeron" (rather than ieron). The remaining forms gain a written accent over the letter "i."

creer:

• creí 
• creíste
• creyó 
• creímos
• creísteis
• creyeron

Exceptions to this rule include:

• traer
• atraer
• distraer

Verbs that end in 'uir' change in the same way, but the written accent over the letter "i" only occurs in the yo form:

huir:

• huí
• huiste
• huyó
• huimos
• huisteis
• huyeron

Some verbs actually change meaning, depending upon whether they are used in the preterite or the imperfect:

• Conocí a Juan hace cinco años.

I met Juan five years ago.

• En aquella época conocíamos muy bien la ciudad.

At that time we knew the city very well.

• María quiso comprar la casa.

Maria tried to buy the house.
(completed action)

• Juan quería comprar la casa.

Juan wanted to buy the house.
(no definite beginning or end)

The preterite is used in the following situations: 

• For actions that can be viewed as single events
• For actions that were repeated a specific number of times
• For actions that occurred during a specific period of time
• For actions that were part of a chain of events
• To state the beginning or the end of an action

There are a number of verbs that are irregular in the preterite that follow a particular pattern. The pattern is that while their stems change, they all take the following endings:

• -e
• iste
• o
• imos
• isteis
• ieron

Some verbs actually change meaning, depending upon whether they are used in the preterite or the imperfect. These include:

• conocer
• (no) querer
• saber
• poder
• tener

Some words and phrases indicate specific time frames, and therefore signal the use of the preterite:

• ayer (yesterday)
• anteayer (the day before yesterday)
• anoche (last night)
• desde el primer momento (from the first moment)
• durante dos siglos (for two centuries)
• el otro día (the other day)
• en ese momento (at that moment)
• entonces (then)
• esta mañana (this morning)
• esta tarde (this afternoon)
• la semana pasada (last week)
• el mes pasado (last month)
• el año pasado (last year)
• hace dos días, años (two days, years ago)
• ayer por la mañana/tarde (yesterday morning/afternoon)