Si clauses 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 depends on the tense of the si clause. In other words, the tense of the two clauses follow a prescribed sequence.
Si + Present Indicative
| si clause | result clause |
| si + present indicative (possible condition) |
present indicative or future or imperative |
This first type of si clause is used in cases where the condition may be fulfilled and thus the consequence is seen as possible. Si clauses in the present indicative can be followed by result clauses in the present indicative, in the future, or in the imperative:
Si veo que ellos me contestan en inglés, sigo hablando con ellos en inglés.
If I see that they answer me in English, I keep talking to them in English.
Note that either the si clause or the result clause may begin a sentence, but the same tenses remain specific to each clause.
Si + Past (Imperfect) Subjunctive
| si clause | result clause |
| si + past (imperfect) subjunctive (contrary to current facts) |
conditional |
This second type of si clause is contrary to fact in the present. The consequence is thus seen as impossible. Note that in Spanish, the imperfect (past) subjunctive is used in the si clause, never the conditional.
Si fuera lugar u objeto, yo diría que la televisión.If it was (were) a place or an object, I would say television.
Si + Pluperfect Subjunctive
| si clause | result clause |
| si + pluperfect subjunctive (contrary to past facts) |
past conditional |
This last type of si clause is used for situations that are contrary to past fact. The result clause thus expresses an unrealized past possibility and it is in the past conditional tense.
Si hubiera estudiado más, habría sacado notas mejores. If I had studied more, I would have got better grades.
Sometimes, when the result clause refers to something still valid in the present or to a general statement, the past conditional can be replaced by the (simple) conditional.
Si hubiera estudiado más, ahora tendría un trabajo mejor.If I had studied more, I would have a better job now.
However, in spoken Spanish, the past conditional or the simple conditional are often replaced by the pluperfect subjunctive for this kind of hypothetical clauses. The resulting structure would be in such cases a sentence containing two pluperfect subjunctive verbs.
Si yo te hubiera dicho que no hablo inglés, me hubieras despedido.If I had told you that I do not speak English, you would have fired me.