What tense should I use in an "if"/"si" clause.

The "si" clause in French can use a few different tenses depending on what kind of hypothesis you want to talk about. There are three main uses that each use a different combination of tenses. 1) A hypothesis on the future. This is usually used to express something that is likely to happen or has an obvious consequence. This clause uses Si + present + future. "Si tu ne cours pas, tu vas rater le bus" - "If you don't run, you will miss the bus." 2) A hypothesis on the present. This is usually used to express something that is unlikely. This clause uses Si + imperfect + present conditional. "Si j'étais jeune, je voyagerais" - "If I were young, I would travel." Note that for this clause, in English we can also say "If I was young" instead of "If I were young". 3) A hypothesis on the past. This is used to express something that would've happened, or is impossible. This clause uses Si + past perfect + conditional perfect. “Si je n’avais pas couru, j’aurais raté le bus” - “If I hadn’t run I would’ve missed the bus.”Some extra notes:-It doesn’t matter which order the clauses are in, as long as the whole clause stays together. For example, you could say “Tu vas rater le bus, si tu ne cours pas.” -If you want to add another condition, you can use “que” + the subjunctive. For example, “Si vous appelez et que je sois occupé, laissez un message.” - “If you call and I’m busy, leave a message.”