What is the conditional perfect, and how do you use it?

The conditional perfect, also called the past conditional (conditionnel passé), is used to express what would have happened. To form the conditional perfect, use the conditional of avoiror être, plus a past participle, for example 'j'aurais travaillé' - 'I would have worked'. Here we see the first person conditional of avoir - 'j'aurais' - 'I would have', combined with the past participle of travailler - 'travaillé'- 'worked'. Verbs which take êtrein the perfect tense, including reflexive verbs, also do so in the conditional perfect. Remember to make the past participle agree with the subject when using être: 'elle serait venue' - 'she would have come'. So here we have the third person conditional of être - 'elle serait', plus the past participle of venir - 'venu' - with an 'e' added to make it agree with the female subject. The conditional perfect is often used in 'if...then' statements. This requires a 'si' clause in the pluperfect tense, followed by a main clause in the conditional perfect, just like in English. For example: 'Si j'avais su, j'aurais travaillé un peu plus' ('If I had known, I would have worked a bit more'). Let's break this down. First we have the pluperfect (the imperfect of avoir or être, - 'j'avais', I had - plus a past participle - 'su', known). Combined with 'si', this reads 'if I had known'. In the main clause of the sentence, we use the conditional perfect, to express what would have happened - in this case, what the speaker would have done differently - if the condition laid out in the pluperfect had been fulfilled (if they had known). As before, we use a conditional form of avoir – ‘j’aurais’, plus a past participle – ‘travaillé’. The same applies to verbs which take être, e.g.: ‘si j’étais partie en vacances, j’aurais été plus heureuse’ – ‘if I had gone on holiday, I would have been happier’.