Preterite vs imperfect in Spanish: which past tense

Spanish has two everyday past tenses, and they describe the same moment in different ways. The preterite views an action as completed: a finished event with a clear start or end. The imperfect views it as ongoing or habitual: background, descriptions and repeated actions, with no focus on the end.

The rule of thumb is short. A finished event takes the preterite; the setting, habit or description around it takes the imperfect. Compare Ayer comí paella (“Yesterday I ate paella”, one finished meal) with De niño comía paella los domingos (“As a child I used to eat paella on Sundays”, a repeated habit).

Preterite: completed actions

Choose the preterite when you report a single finished event, especially with a specific time marker such as ayer, anoche, el lunes or de repente.

Anoche vi una película.
Last night I watched a movie.

El lunes empezó el curso.
On Monday the course started.

The preterite is also the tense of a sequence: one completed action after another, each pushing the story forward.

Llegué, comí y me fui.
I arrived, ate and left.

Time-ago phrases work the same way: hace + time with the preterite means “ago”, as in Llegué hace una hora (“I arrived an hour ago”).

Imperfect: background, habits and descriptions

Choose the imperfect to set the scene. It describes how things looked or felt, gives age, time of day and weather in the past, and covers anything you would say in English with “used to” or “was -ing”. Markers like siempre, todos los días and mientras often point to it.

Cuando era niño, vivíamos cerca del mar.
When I was a child, we lived near the sea.

Todos los días caminaba al trabajo.
Every day I used to walk to work.

Llovía y hacía frío.
It was raining and it was cold.

None of these has a clear endpoint. They are the background of a story rather than its events.

Two tenses in one sentence

The two tenses often meet in a single sentence: the imperfect paints the ongoing background, and a preterite event interrupts it.

Mientras estudiaba, sonó el teléfono.
While I was studying, the phone rang.

Dormíamos cuando empezó la tormenta.
We were sleeping when the storm started.

The longer, scene-setting action stays in the imperfect (estudiaba, dormíamos); the sudden event that cuts in takes the preterite (sonó, empezó).

Verbs that change meaning

A handful of common verbs shift their sense depending on the aspect. In the imperfect they describe an ongoing state; in the preterite they mark the moment that state began or a completed attempt.

The pair conocer shows the pattern clearly. The imperfect is the steady state of knowing someone; the preterite is the single moment you first met them.

Ya conocía a María, pero ayer conocí a su hermano.
I already knew María, but yesterday I met her brother.

Common mistakes

Imperfect for a finished event

Ayer comía paella. → Ayer comí paella.
Yesterday I ate paella.

A single, completed action at a specific time takes the preterite, not the imperfect.

Preterite for a description

El cielo estuvo azul y hizo sol. → El cielo estaba azul y hacía sol.
The sky was blue and it was sunny.

Setting the scene — weather, mood, how things looked — is ongoing background, so it stays in the imperfect.

Preterite for “was -ing”

Mientras estudié, sonó el teléfono. → Mientras estudiaba, sonó el teléfono.
While I was studying, the phone rang.

English “was studying” describes an action in progress, which is the imperfect; only the interrupting event uses the preterite.

Telling these two past tenses apart is a meaning decision you remake in every sentence: is this a finished event, or the scene around it? Fluera drops both tenses into short past-tense sentences so you choose the aspect that fits, then read and hear the whole sentence in context. Lean on that loop to practice Spanish until the preterite-imperfect contrast stops feeling like a rule and starts feeling like a choice.

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