Preterite or imperfect
To emphasize the start or completion of a past action, even, or state (physical or mental)
Preterite
To narrate past actions that occurred within a delimited time period or that were repeated a number of times
Preterite
one time
una vez
every day
cada dia
"I visited my family in Monterrey many times"
Preterite
To provide background information, such as weather and time, in which events or actions evolved or occurred in the past
Imperfect
To summarize opinions, attitudes, and beliefs about past physical and mental states, actions, and events
Preterite
yesterday morning
ayer por la manana
a lot
mucho
"We were all waiting patiently to board the plane"
Imperfect
To describe actions in progress in the past without emphasis on when they started or ended
Imperfect
To describe actions in progress in the past without emphasis on when they started or ended
Imperfect
last week
la semana pasada
never
nunca
"It was ten o'clock in the morning. It was very hot that day. There wasn't anybody in the airport."
Imperfect
To express repetitive or habitual actions in the past (what one used to do)
Imperfect
To describe one's age
Imperfect
last month
el mes pasado
at that time
en aquella epoca
"The trip seemed very long to me"
Preterite
To narrate a sequence of completed past actions (implying that one action or even finishes before the next begins)
Preterite
To anticipate what was going to happen with "ir a + infinitive"
Imperfect
then
entonces
several times
varias veces
"I stopped looking for work after accepting the job"
Preterite