« Quand je suis arrivé, le train était déjà parti. » Two past events, one earlier than the other — the earlier one takes the plus-que-parfait, French’s “past before the past”.
The quick version — the full lesson is below. More shorts →
Take the imparfait of avoir or être, add the past participle — the same avoir/être split as the passé composé:
It sets the stage one step further back than the main narrative: « Il a raté le contrôle parce qu’il n’avait pas révisé. » (He failed the test because he hadn’t studied.) English often drops “had” — French does not.
Past hypotheticals — things that can no longer happen — pair si + plus-que-parfait with the conditionnel passé: « Si j’avais su, je ne serais pas venu. » (If I had known, I wouldn’t have come.) Alone, « Si j’avais su ! » is a classic sigh of regret.
After a past reporting verb, a passé composé shifts back: « J’ai fini » → Il a dit qu’il avait fini. (He said he had finished.)
Ask: did it happen BEFORE another past event you’re talking about? Earlier event → plus-que-parfait. Main event → passé composé. « Elle avait déjà commandé quand je suis arrivé. »
Exactly the same list as the passé composé (aller, venir, partir… + all reflexives), with the same agreement. Refresh the list in French past tenses.
No — never a conditional after si. It’s si j’avais su. The full si-system is mapped in French si clauses, and the imparfait half in imparfait vs passé composé.
Keep going: Reported speech is where this tense lives — see the full shift table in French reported speech.

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