Conditional perfect - Wikipedia
https://en.wikipedia.org/wiki/Conditional_perfectFrench expresses past counterfactual conditional sentences in exactly the same way as English does: the if clause uses the had + past participle (pluperfect) form, while the then clause uses the would have + past participle form, where the equivalent of would have is the conditional of the auxiliary (avoir or être) used in all perfect constructions for the verb in question. Example: • Si on l'avait su [pluperfect indicative], on aurait pu [conditional perfect] l'empêcher.