If you have been learning Spanish for a few months, you have hit the wall: two past tenses, both apparently meaning “I did” or “I was doing” — and no obvious rule for which one to use.

The frustrating truth is that most textbooks explain this poorly. They give you long lists of rules and exceptions that are hard to remember in the middle of a real conversation.

This guide gives you a single mental model that covers most cases — and then builds from there.

The Core Mental Model

Picture a stage with a backdrop and actors:

  • The imperfect (imperfecto) is the backdrop — the setting, the ongoing situation, the background description. It was already happening.
  • The preterite (indefinido) is the action on stage — the specific event that occurred, completed, and moved the story forward.

Llovía cuando salí de casa. It was raining (backdrop) when I left the house (action).

One verb sets the scene. The other moves the story forward. That is the key distinction.

When to Use the Preterite (Indefinido)

Use the preterite for completed actions — things that happened once, at a specific moment, and are done.

1. A single completed event

Ayer comí una paella. — Yesterday I ate a paella. Llegaron a las ocho. — They arrived at eight.

2. A sequence of events

Me levanté, me duché y salí. — I got up, showered, and left.

Each action is complete before the next begins. Preterite for all three.

3. An action that happened a specific number of times

Fui a España tres veces. — I went to Spain three times. Llamé dos veces. — I called twice.

4. An action with a clear beginning and/or end

Vivió en Madrid durante dos años. — He lived in Madrid for two years. (and then stopped) Estudié de las tres a las cinco. — I studied from three to five.

When to Use the Imperfect (Imperfecto)

Use the imperfect for ongoing, habitual, or descriptive situations in the past.

1. Habitual or repeated past actions (“used to”)

De niño, comía cereal cada mañana. — As a child, I used to eat cereal every morning. Los sábados íbamos al mercado. — On Saturdays, we would go to the market.

2. Background descriptions — setting the scene

Hacía sol y había mucha gente en la playa. It was sunny and there were a lot of people on the beach.

3. Ongoing actions that were interrupted

Dormía cuando sonó el teléfono. I was sleeping (imperfect) when the phone rang (preterite).

4. Telling the time in the past

Eran las dos de la tarde. — It was two in the afternoon.

5. Age in the past

Tenía ocho años cuando aprendí a nadar. — I was eight when I learned to swim.

6. Emotions, mental states, and descriptions in the past

Estaba cansado y no quería salir. I was tired and didn’t want to go out.

Time Markers That Signal Each Tense

Certain words typically accompany each tense. They are not absolute rules, but they are strong signals:

Preterite markers:

  • ayer (yesterday), anteayer (the day before yesterday)
  • el lunes pasado (last Monday)
  • hace dos años (two years ago)
  • de repente (suddenly)
  • una vez, dos veces (once, twice)
  • finalmente, por fin (finally)

Imperfect markers:

  • siempre (always), nunca (never)
  • a veces (sometimes), a menudo (often)
  • todos los días (every day)
  • cuando era niño/a (when I was a child)
  • normalmente, generalmente (normally, generally)

Both Tenses in the Same Sentence

This is where the distinction becomes most visible — and most useful:

Leía un libro cuando llegó María. I was reading a book (imperfect — ongoing) when María arrived (preterite — completed event).

Hacía mucho calor, así que decidimos ir a la piscina. It was very hot (imperfect — background state), so we decided to go to the pool (preterite — decision made).

Quería salir pero empezó a llover. I wanted to go out (imperfect — state) but it started to rain (preterite — event).

The Most Common Mistakes

1. Using preterite for habitual past actions

✗ Cuando era niño, comí cereal cada mañana. ✓ Cuando era niño, comía cereal cada mañana.

2. Using imperfect for a clearly completed event

✗ Ayer trabajaba hasta las ocho. ✓ Ayer trabajé hasta las ocho. — Yesterday I worked until eight.

3. Forgetting irregular preterite forms Verbs like ser/ir (fui, fuiste, fue), tener (tuve), hacer (hice), and estar (estuve) are irregular in the preterite. If you are rusty on these, the Irregular Verbs guide is worth reviewing.

Keep Practising

Reading the rule is one thing — using it under pressure in a conversation is another. The Conjugation drill in the Gym lets you practise the indefinido and imperfecto with 30 verbs until the forms become automatic.

Start with the backdrop/action mental model. Apply it every time you write a Spanish sentence in the past. Within a few weeks, you will stop thinking about the rule — and start feeling the difference.