What are 'si' clauses?

'Si' clauses are sometimes known as conditionals. They're used to introduce a hypothetical action which is based on another action. For example, s'il fait beau, je sors - if it is sunny, I go out. Here, the going out is dependent on the weather being nice.There are three types of 'si' clauses: 1) Potentiel - in these, the second action could happen. - present + present S'il fait beau, je sors - If it is sunny, I go out. - present + future S'il fait beau, je sortirai - If it is sunny, I will go out. - present + imperative S'il fait beau, sors - If it is sunny, go out! - passé composé + present/future/imperative Si tu l'as vu, tu dois me dire - If you have seen it, you must tell me Si tu l'as vu, tu devras me dire plus tard - If you have seen it, you will have to tell me later Si tu l'as vu, dites-moi! - If you have seen it, tell me! 2) Iréel du présent - in these, the second action is unlikely - imperfect + conditional S'il faisait beau, je sortirais - If it was sunny, I would go out 3) Iréel du passé - in these, the second action is now impossible, given the first didn't happen - pluperfect + conditional past S'il avait fait beau, je serais sortie - If it had been sunny, I would have gone out And there you have it, 'si' clauses! Quick final note: the 'si' part does not need to be first in the sentence, just like in English - we say 'I would have gone out if it had been sunny' just as we say 'if it had been sunny, I would have gone out'. The verb that follows the 'si' stays in the same tense as above, just swap the two halves around!