Quick answer
Si llueve, no salgo · Si tuviera tiempo, iría · Si hubiera sabido, habría venido
Three patterns: real, unlikely, impossible. Each pairs one fixed tense with another.
The three patterns
| Type | si clause | Result clause |
|---|---|---|
| 1 — real, likely | present indicative | present, future or ir a |
| 2 — unlikely, hypothetical | imperfect subjunctive | conditional (-ría) |
| 3 — impossible, past | pluperfect subjunctive (hubiera + participle) | conditional perfect (habría + participle) |
Either half can come first. With the si clause first, a comma separates them.
Type 1: it may well happen
Present indicative after si. This is the type you use most in daily life.
Never a future tense directly after si: Si tendrás tiempo does not exist.
Type 2: unlikely or plainly imaginary
Imperfect subjunctive after si, conditional in the other half.
The conditional stays out of the si clause. Si tendría and si sería are simply wrong.
Type 3: it is too late now
Both halves compound: hubiera + participle after si, habría + participle in the result. In speech hubiera often appears in both halves.
Memory trick
Nothing with -ría and nothing with a future ending ever follows si. The si clause takes present, imperfect subjunctive, or hubiera + participle.
Typical mistakes
Si tendría dinero, compraría un coche.
Si tuviera dinero, compraría un coche.
The conditional belongs in the result half. After si you need the imperfect subjunctive.
Si llegarás tarde, avísame.
Si llegas tarde, avísame.
A real condition takes the plain present after si, never the future.
Si habría estudiado, habría aprobado.
Si hubiera estudiado, habría aprobado.
The impossible past takes hubiera + participle in the si clause and habría + participle in the result.
Check yourself
Si ___ más tiempo, viajaría por España. (tener)