Si clauses (if, or if/then clauses in English) indicate possibilities, which may or may not become reality. They refer to the present, past, and future. These conditional sentences have two parts: the condition, or si clause, and the main or result clause which indicates what will happen if the condition of the si clause is met. The tense of the result clause/part of the sentence depends on the tense of the si clause/part of the sentence. It’s like a mathematical formula.
si + présent: POSSIBLE
This first type of si clause is used in cases where the condition may be fulfilled/may happen, so the consequence is seen as possible. In the following dialogue, notice the si clauses in the present followed by result clauses in the present, in the future and in the imperative:
TIP: Si does not have to start the sentence. The tenses stay the same whichever way you say the sentence: “Qu'est-ce que tu feras demain si tu trouves l'amour de ta vie?' [What will you do tomorrow if you meet the love of your life] is the same as “Si tu trouves l’amour de ta vie demain, qu’est ce que tu feras?” [If you meet the love of your life tomorrow, what will you do?].
si + imperfect (imparfait): IMPOSSIBLE
This second type of si clause is about impossible things.
si + pluperfect (plus-que-parfait): IMPOSSIBLE/DID NOT HAPPEN
This last type of si clause is used for situations that are about things that did not happen in the past.
Distinguish between si clauses (if -clauses) and questions that are reported in indirect speech. Observe the difference between these two sentences: