French si-clauses (if-clauses) follow three fixed tense patterns depending on how real or hypothetical the condition is. For a real, likely condition, si + present pairs with a future or present result: si tu viens, je serai content (if you come, I will be happy).
For a hypothetical or unlikely present condition, si + imparfait pairs with the conditionnel présent: si j'avais plus de temps, je voyagerais davantage (if I had more time, I would travel more). For an unreal past condition — something that didn't happen — si + plus-que-parfait pairs with the conditionnel passé: si j'avais su, je serais venu (if I had known, I would have come). Crucially, si is never directly followed by a future or a conditionnel tense, even though the result clause often is.