"Should" vs "Would" in conditionnel passé

Question

I am having some difficulty understanding when the conditionnel passé is meant to indicate "should" vs "would." Is it just context dependent or is there something specific I should be looking for to indicate these differences?

Merci beaucoup!

Céline Pickard · Accepted Answer

Bonjour Benjamin,
It all depends on what you wish to express.
If you wish to say:
- "should have [done]" → conjugate "devoir" in Le Conditionnel Passé + infinitive:

I should have left → j'aurais dû partir
I should have been there → J'aurais dû être là

- "would have [done]" -> conjugate the main verb in Le Conditionnel Passé:

If I'd known, I would have left earlier → Si j'avais su, je serais parti plus tôt
I would have eaten his cake too → J'aurais mangé son gâteau aussi

- "could have [done]" → conjugate "pouvoir" in Le Conditionnel Passé + infinitive:

If you'd warned me you'd be late, I could have left home later → Si tu m'avais prévenu que tu serais en retard, j'aurais pu partir de chez moi plus tard
I could have helped you with your exam preparations → J'aurais pu t'aider à te préparer pour tes examens

I hope this is helpful.
Bonne journée !