One of the most common questions I answer during a tutoring session is the following: "What are 'si clauses'?
"Si" means "if" in Spanish. A "si clause" would take the following structure in English: if ____ occurred, ____ would happen. For example, if you had arrived on time, I would not have been late. Si hubieras llegado a tiempo, yo no habría sido tarde. If you were to buy eggs, I could make a cake. Si compraras los huevos, podría hacer un pastel.
Caution! I'm going to cover the grammatical rules involved in "si clauses" over the next few lines. This is very advanced Spanish. If you do not understand, don't worry! There's only so much I can cover during a single post. I'm always available to provide more in-depth explanations on this and other subjects.
In Spanish, the structure of a "si clause" depends on the scenario. Whenever the verb in the first part of the sentence takes the past subjunctive form, the verb in the second part of the sentence takes the conditional form. Looking at the previous example, "hubieras" and "compraras" are in the past subjunctive, while "habría" and "podría" are in the conditional.
If the verb in the first part of the sentence is not in the past subjunctive form, the verb in the second part of the sentence should never take the conditional form. For example, if the first verb is in the future or present tense, the second verb should not be conditional: If you buy eggs, I will make cake. Si compras los huevos, haré un pastel. If you remember these two rules, you should be able to master "si clauses."