Lessons

Imperfect tense - uses (II)

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The imperfect past (pretérito imperfecto) is used for past actions in progress or simultaneous actions.

What this structure is for (two actions in the past)

  • Action A was in progress when Action B happened (and interrupted it)imperfecto + cuando + indefinido
  • Two actions were happening at the same time (no interruption) → mientras + imperfecto + imperfecto

Think in images: “background” vs “event”

Imperfecto

Background / ongoing process

What was going on? Not finished yet.

English clue: often was/were + -ing

Indefinido (preterite)

Event / finished action

What happened? A “point” on the timeline.

English clue: often simple past (rang, arrived, started)

Pattern 1: Imperfecto + cuando + indefinido (interruption)

  • Imperfecto = what was in progress
  • cuando = the moment it changes
  • Indefinido = the interrupting event
Correct

Revisaba el examen cuando terminó el tiempo.

I was reviewing the exam when time ran out.

Common mistake

Revisé el examen cuando terminaba el tiempo.

Problem: the ongoing action should be imperfecto, and the interrupting event should be indefinido.

Pattern 2: Mientras + imperfecto + imperfecto (simultaneous actions)

  • mientras = “during the time that…”
  • Usually, both verbs are in imperfecto because both actions are “in progress”.
Correct

Mientras corregía el examen, revisaba las notas.

While I was grading the exam, I was checking the notes.

Correct (same idea, different order)

Pensaba en la prueba mientras esperaba los resultados.

I was thinking about the test while I was waiting for the results.

Common mistake

Mientras esperaba las notas, revisé los errores.

Problem: with simultaneous actions, you normally keep both in imperfecto: revisaba.

Quick self-check: choose the tense in 3 steps

  1. Do I have one ongoing action and one “sudden” event?

    Yes → ongoing = imperfecto, event = indefinido (often with cuando).

  2. Are both actions happening in parallel?

    Yes → imperfecto + imperfecto (often with mientras).

  3. What is the “headline” of the story?

    The headline event is typically indefinido; the background details are imperfecto.

What to pay attention to (typical learner doubts)

  • “cuando” does not automatically mean indefinido.

    It depends on meaning: interruption → indefinido for the interrupting action.

  • With “mientras”, preterite sounds like “I finished it”.

    So Mientras esperaba, revisé… suggests you completed the review during that waiting time, not that it was simply ongoing.

  • English can hide the difference.

    In English, both “While I waited, I reviewed…” and “While I was waiting, I was reviewing…” can be acceptable. In Spanish, the tense choice is more explicit.

Mini model sentences you can reuse in conversation

  • Estaba trabajando en un informe cuando el cliente llamó.

  • Mientras el equipo analizaba los datos, yo preparaba la presentación.

  • Leía el contrato cuando me di cuenta de un error.

  1. An action was in progress when another happened ⇒ imperfect + preterite (indefinido).
  2. Two actions were happening at the same time in the past ⇒ imperfect + imperfect.
EstructuraEjemplo
Imperfecto + cuando + indefinidoRevisaba el examen cuando terminó el tiempo. (I was checking/reviewing the exam when time ran out.)

Mientras + imperfecto + imperfecto

Imperfecto + mientras + imperfecto

Mientras corregía el examen, revisaba las notas. (While I was grading the exam, I was checking the notes.)

Pensaba en la prueba mientras esperaba los resultados. (I was thinking about the test while I was waiting for the results.)

Exercise 1: Multiple choice

Instruction: Choose the correct answer

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1. Revisaba la parte teórica cuando ______ el timbre y se acabó el tiempo. Revisaba la parte teórica cuando sonó el timbre y se acabó el tiempo.

I was reviewing the theory part when ______ the bell rang and time ran out.

2. Mientras ______ los exámenes, comparaba las respuestas con la plantilla. Mientras corregía los exámenes, comparaba las respuestas con la plantilla.

While I ______ the exams, I was comparing the answers with the answer key.

3. Pensaba en la convocatoria mientras ______ la nota final. Pensaba en la convocatoria mientras esperaba la nota final.

I was thinking about the exam session while ______ the final grade.

4. Buscábamos diferencias entre nuestras redacciones cuando el profesor ______ la revisión. Buscábamos diferencias entre nuestras redacciones cuando el profesor anunció la revisión.

We were looking for differences between our essays when the teacher ______ the review.

Exercise 2: Rewrite the phrases

Instruction: Combine the two sentences into one using the indicated structure: imperfect + cuando + preterite (ongoing action interrupted) or mientras + imperfect + imperfect (simultaneous actions).

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  1. (cuando) Preparaba la presentación. Sonó el teléfono.
    ⇒ ____________________________________________________________________________________________________ Example
    Preparaba la presentación cuando sonó el teléfono.
    (I was preparing the presentation when the phone rang.)
  2. (cuando) Revisaba los correos. Llegó un mensaje urgente del jefe.
    ⇒ ____________________________________________________________________________________________________ Example
    Revisaba los correos cuando llegó un mensaje urgente del jefe.
    (I was checking emails when an urgent message from the boss arrived.)
  3. (cuando) Esperaba el autobús. Empezó a llover.
    ⇒ ____________________________________________________________________________________________________ Example
    Esperaba el autobús cuando empezó a llover.
    (I was waiting for the bus when it started to rain.)
  4. (Mientras) Hablaba con un cliente. Mi compañero buscaba los datos en el ordenador.
    ⇒ ____________________________________________________________________________________________________ Example
    Mientras hablaba con un cliente, mi compañero buscaba los datos en el ordenador.
    (While I was talking with a client, my coworker was looking for the data on the computer.)

Exercise 3: Multiple Choice

Instruction: Choose the correct sentence.

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1.
Incorrect: the action in progress should be in the imperfect (was studying) and the punctual interruption in the preterite (rang); here they are reversed.
2.
Incorrect: since they are simultaneous actions, both must be in the imperfect (was reviewing), not in the preterite (reviewed).

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Alessia Amoroso

Master of Languages, Cultures, Communication

Università degli Studi di Modena e Reggio Emilia

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Last Updated:

Monday, 07/09/2026 13:40