Spanish “SI clauses” (or conditional sentences) express what could occur if a condition is fulfilled.
We can find three different kinds of si clauses:
1.POSSIBLE OR LIKELY SITUATIONS: if + indicative
In this group we can find three different constructions:
A. Si + present + present: It is used for things that happen (regularly) if a condition is fulfilled and to express universal truths.
Si llueve y no tienes paraguas, te mojas. If it rains and you don’t have an umbrella, you get wet.
Si comes mucho, engordas. If you eat a lot, you get fatter.
B. Si + present + future: it is used for things that will happen if the condition is met (in the present).
Si me ayudas, te daré 100 dólares. If you help me I´ll give you 100 dollars.
C. Si + presente + imperative: it is used to give an order (imperative) dependent on the condition being met.
Si vienes a España, avísame. If you come to Spain, let me know.
2. UNLIKELY OR CURRENTLY CONTRARY SITUATIONS: if + subjuntive (imperfect)
Si + imperfect subjunctive + conditional: to express a unlikely or currently contrary situations in present time, the imperfect subjunctive is used in the si-clause and the conditional in the main clause. The situation is unlikely or not currently true but if something changed, it could happen.
Si tuviera mucho dinero, te ayudaría. If I had a lot of money, I would help you.
3. IMPOSSIBLE SITUATIONS: if + subjuntive (pluperfect)
Si + pluperfect subjunctive + conditional perfect / pluperfect subjunctive: to express a situation that would have happened if a condition had been fulfilled. It’s an impossible situation since it’s in past time, so we can’t change it.
Si hubiera sabido tu dirección, te habría enviado la invitación.
Si hubiera sabido que ella estaba aquí, te hubiera enviado la invitación.
If I had known your address, I would sent the invitation to you.
Si supiera tu teléfono, te llamaría. If I knew your telephone number, I would call you.
Te llamaría si supiera tu teléfono. I would call you if I knew your telephone number.