Spanish grammar – conditional (if-would) clauses
In order to say what you do or would do if a condition exists, these formulas apply:
1. si + present indicative + present indicative
Si ella te quiere, puedes casarte con ella sin problema.
If she loves you, you can marry her without any problem.
The word si never triggers a present-subjunctive verb. If the first clause is not contrary to fact, both verbs will be in the present indicative.
2. si + past subjunctive + conditional
Si tú fueras más joven, podrías jugar beisbol profesional.
If you were younger, you would be able to play professional baseball.
Here, the word si triggers a past-subjunctive verb in the first clause, and a conditional verb appears in the second clause. The situation is contrary to fact—you are not younger, but if you were, you would be able to play professional baseball.
3. como si + past subjunctive
Juan come como si nunca hubiera comido.
Juan eats as if he had never eaten.
The words como si always trigger a past-subjunctive verb in the second clause, because they indicate a hypothetical or contrary-to-fact situation.
Here is an exercise that you may find helpful: