In short

The conditionnel passé is a compound tense meaning “would have (done)”. Form it with avoir or être in the conditional present plus the past participle: j’aurais fini, je serais parti.

The rule

You already know the conditionnel présent (Lesson 34) and how compound tenses work with a helper verb plus a past participle (Lessons 20-21). The conditional past simply combines them: put the auxiliary in the conditional present, then add the past participle.

Building block: auxiliary (conditional present) + past participle

• With avoir: j’aurais mangé (I would have eaten), tu aurais dit (you would have said).
• With être: je serais venu(e) (I would have come), elle serait tombée (she would have fallen).

The choice of auxiliary and the agreement rules are exactly the same as in the passé composé:

• Most verbs take avoir; the participle then agrees only with a preceding direct object: les lettres que j’aurais écrites.
• Verbs of movement/state (the “house of être”: aller, venir, partir, arriver, rester, monter, descendre, entrer, sortir, tomber, naître, mourir, devenir, retourner) and all pronominal verbs take être; the participle then agrees with the subject: elle serait restée, ils se seraient levés.

Core meaning: an action that would have happened under some (usually unreal, now-impossible) condition. It looks back at a past that did not come true.

Regret and reproach: j’aurais dû

The conditional past of modal verbs expresses regret (about yourself) or reproach (toward someone else). This is one of the most useful everyday functions.

• devoir -> j’aurais dû = “I should have” / “I ought to have”: J’aurais dû l’écouter. (I should have listened to him.)
• pouvoir -> j’aurais pu = “I could have”: Tu aurais pu me prévenir ! (You could have warned me!)
• vouloir -> j’aurais voulu = “I would have liked”: J’aurais voulu rester plus longtemps.
• falloir -> il aurait fallu = “it would have been necessary / we should have”: Il aurait fallu partir plus tôt.

Note that these modals always take avoir and their participle (dû, pu, voulu, fallu) does not vary.

Result clause of si type 3 (paired with plus-que-parfait)

In the third type of hypothetical sentence - an unreal condition in the past - the si clause uses the plus-que-parfait (Lesson 33) and the result clause uses the conditionnel passé. This describes something that could have been but never happened.

• si + plus-que-parfait -> conditionnel passé
• Si j’avais su, je ne serais pas venu. (If I had known, I would not have come.)
• Si tu avais étudié, tu aurais réussi l’examen. (If you had studied, you would have passed the exam.)

The order can be reversed with no change of meaning: Je ne serais pas venu si j’avais su. You will study the full family of si clauses in Lesson 36; this lesson gives you the past (type 3) result half.

Forms & patterns

Auxiliary avoir (conditional present) + past participle - example: parler

Auxiliary être (conditional present) + past participle - example: partir (agrees with subject)

Common modals for regret / reproach

Examples

Common mistakes

• J’aurais dû fait attention -> J’aurais dû faire attention - “should have done” is aurais dû + infinitive: the “have” is already in aurais, so do not copy the English participle.
• Si j’aurais su -> Si j’avais su - never put a conditional after si; the condition takes the plus-que-parfait.
• elle serait venu -> elle serait venue - with être the participle agrees with the subject (feminine here).
• j’ai aurais parlé -> j’aurais parlé - use only one auxiliary, in the conditional present; do not stack ai and aurais.
• je serais mangé -> j’aurais mangé - manger takes avoir, not être; keep the passé composé auxiliary choice.
• j’aurais venu -> je serais venu - venir is an être verb even in the conditional past.

Tips

• Build it in two steps: first say the auxiliary in the conditional (aurais / serais), then add the participle - the same participle you already use in the passé composé.
• The auxiliary (avoir vs être) and all agreement rules are identical to the passé composé; if you know Lessons 20-21, you know them here.
• For English “should have / could have / would have liked”, reach for j’aurais dû / j’aurais pu / j’aurais voulu.
• The type-3 pattern is a fixed pair: si + plus-que-parfait on one side, conditionnel passé on the other. Never a conditional after si.
• Either half can come first: Je serais resté si j’avais pu = Si j’avais pu, je serais resté.
• To soften a reproach, prefer the conditional past over a blunt past tense: Tu aurais pu me le dire is gentler than Tu ne me l’as pas dit.