Both the passé composé and the imparfait describe past events. The difference is not when something happened. The difference is how the speaker chooses to present it.

Think of the two tenses like this:

• The passé composé is like a photo. It presents an action as a complete event.
• The imparfait is like a video. It presents an action, state, or situation as continuing or in progress.

The same real-life event can sometimes be viewed either way, depending on what the speaker wants to emphasise.

Use the passé composé when you present an event as complete

The passé composé is formed with avoir or être plus a past participle.

Use it for:

A single completed event

• J’ai mangé une pomme.
  “I ate an apple.”
• Il est sorti à midi.
  “He went out at noon.”

A sequence of completed actions

• Elle est entrée, elle a vu le désordre et elle a nettoyé.
  “She came in, saw the mess and cleaned it up.”

An event that occurs during an ongoing situation

• Je lisais quand le téléphone a sonné.
  “I was reading when the telephone rang.”

The reading provides the background. The telephone ringing is the completed event.

Use the imparfait to describe a situation

The imparfait is formed from the present-tense nous form by removing -ons and adding:

-ais, -ais, -ait, -ions, -iez, -aient

It answers questions such as:

• What was happening?
• What was it like?
• What used to happen?

Use it for:

Actions in progress

• Il dormait.
  “He was sleeping.”

The sentence simply describes the situation. It says nothing about when the sleeping ended.

Habits and repeated actions

• Chaque été, nous allions à la plage.
  “Every summer we went to the beach.”
• Elle fumait beaucoup.
  “She used to smoke a lot.”

Descriptions

• Il faisait beau.
  “The weather was nice.”
• La maison était vieille.
  “The house was old.”
• Elle avait peur.
  “She was afraid.”

These describe what things were like rather than reporting events.

Background situations

• Les gens attendaient le bus quand l’accident est arrivé.
  “The people were waiting for the bus when the accident happened.”

The waiting is the background situation. The accident is the completed event.

A useful question to ask

Instead of asking:

“Was the action finished?”

ask:

“Am I describing a situation, or am I presenting an event?”

If you are describing a situation, the imparfait is usually the right choice.

If you are reporting an event, the passé composé is usually the right choice.

Helpful clue words

Certain words often suggest one tense or the other, although they are not absolute rules.

The passé composé often appears with words such as:

• soudain (suddenly)
• tout à coup (all of a sudden)
• une fois (once)
• ce jour-là (that day)

The imparfait often appears with words such as:

• souvent (often)
• toujours (always)
• chaque jour (every day)
• d’habitude (usually)

Notice that pendant does not automatically require the imparfait. It can be used with either tense.

• J’ai travaillé pendant trois heures.
  “I worked for three hours.”
• Pendant que je travaillais, le téléphone a sonné.
  “While I was working, the telephone rang.”

Verbs whose meaning changes

Some verbs have noticeably different meanings depending on the tense.

Savoir

• Je savais. “I knew.”
• J’ai su. “I found out.”

Pouvoir

• Je pouvais. “I was able to.”
• J’ai pu. “I managed to.”

These differences arise because the passé composé presents a completed event, while the imparfait presents an ongoing state.

Compare these pairs

• Il a plu.
  “It rained.”
• Il pleuvait.
  “It was raining.”

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• Nous avons couru dix kilomètres.
  “We ran ten kilometres.”
• Nous courions tous les jours.
  “We ran every day.”

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• Elle a eu vingt ans.
  “She turned twenty.”
• Elle avait vingt ans.
  “She was twenty years old.”

A common pattern

One tense often provides the background while the other introduces a new event.

• Je regardais la télé quand mon ami est arrivé.
  “I was watching TV when my friend arrived.”
• Pendant qu’elle préparait le dîner, le chat a cassé un verre.
  “While she was preparing dinner, the cat broke a glass.”

Summary

• Use the passé composé to present an action as a completed event.
• Use the imparfait to describe a situation, a habit, a state, or an action in progress.
• The choice is about how the speaker presents the past, not simply whether the action really ended.
• When both tenses appear together, the imparfait usually describes the background situation, while the passé composé reports the event that occurs within it.