Conjunciones condicionales: si, a menos que

The single most useful conjunction in Spanish is si (if). With three tense pairings, it covers the entire conditional landscape: real situations (if it rains, I won't go), hypothetical situations (if it rained, I wouldn't go), and counterfactual past situations (if it had rained, I wouldn't have gone). The patterns are clean and rigid — once you know which tense goes on each side, you have native-like grammar in a domain English speakers usually mangle for years.

This page covers the three core si patterns, the cardinal sin English speakers commit (si tendría — never), and the peninsular preference for hubiera/hubiese. For unless, provided that, in case, and other non-si conditionals, see advanced conditional conjunctions.

The three conditional patterns at a glance

The pattern is symmetric and the tense pairings are fixed. Spanish does not allow free mixing — each type has its own slot, and crossing them produces ungrammatical or unnatural sentences. Master the three rows above and you have the entire core system.

Type 1: real conditionals — si llueve, no voy

The first conditional describes a real or open possibility in the present or future. The speaker treats the condition as something that genuinely might happen. The form is fixed: si + present indicative in the si clause, and present indicative, future, or imperative in the main clause.

The crucial rule, and the place English speakers slip: after si, you never use the future or the conditional in a real conditional. English allows if you will come; Spanish doesn't. The present indicative does all the future work after si.

This is the most surprising point of the system for English speakers, because English allows several tenses after if (if you come, if you'll come, if you would come). Spanish only allows present indicative after si for real conditions. The future tense and the conditional are banned from the si clause in this pattern, full stop.

Type 2: hypothetical conditionals — si tuviera dinero, lo compraría

The second conditional describes a hypothetical, unlikely, or imagined situation in the present or future. The speaker treats the condition as contrary to current reality or improbable. The form is si + imperfect subjunctive in the si clause, and conditional in the main clause.

The imperfect subjunctive of tener is tuviera (or tuviese — see below); of ser, ir it's fuera/fuese; of saber it's supiera/supiese; of poder it's pudiera/pudiese. These forms power the entire hypothetical conditional system, so they're worth drilling. See imperfect subjunctive forms for the full paradigms.

The cardinal sin: si tendría

The single biggest error English speakers make in Spanish conditionals is using the conditional after si. English allows if I would have time, I would help. Spanish does not — the si clause never takes the conditional. The translation of if I would have in this type is si tuviera, not si tendría.

If you remember nothing else about Spanish conditionals, remember this: si + conditional is always wrong in standard Spanish. This is one of the cleanest "do not" rules in the whole language, and getting it right immediately marks you as someone who has internalised the grammar rather than translated word-for-word from English.

Type 3: counterfactual past — si hubiera tenido, lo habría comprado

The third conditional describes a past situation that didn't happen — the speaker imagines an alternative past. The form is si + pluperfect subjunctive in the si clause, and conditional perfect (or pluperfect subjunctive) in the main clause.

The pluperfect subjunctive is hubiera/hubiese + past participle: hubiera tenido, hubieras salido, hubiéramos hablado. The conditional perfect is habría + past participle: habría comprado, habríamos perdido.

A frequent native-speaker variant: the pluperfect subjunctive in both halves. Si hubiera tenido dinero, me lo hubiera comprado (instead of habría comprado) is fully grammatical and very common in spoken peninsular Spanish. Treat it as an equivalent option — the habría version sounds slightly more careful or written, the hubiera/hubiera version more colloquial. Both are correct.

Peninsular forms: hubiera vs hubiese, tuviera vs tuviese

Spanish has two parallel sets of imperfect-subjunctive endings: the -ra form (tuviera, hubiera, fuera) and the -se form (tuviese, hubiese, fuese). Both are correct in peninsular Spanish. The differences:

• The -ra forms are more frequent in modern speech everywhere.
• The -se forms retain a slight literary or formal flavour and are more common in writing.
• In conditional si clauses, both are interchangeable: si tuviera / si tuviese, si hubiera / si hubiese.

Pick one set and stick with it for consistency within a sentence, but feel free to use either across utterances. Both are alive and well in peninsular Spanish, although you'll hear -ra more often in conversation.

What about si + future, si + conditional — outside conditionals?

The ban on si + future/conditional applies to conditional si. There is, separately, an indirect-question si meaning whether, which has no tense restrictions:

Distinguishing them is straightforward: conditional si introduces a hypothetical situation with consequences in a main clause (si llueve, no voy); indirect-question si introduces an embedded yes/no question after verbs like saber, preguntar, no estar seguro (no sé si...). Only the conditional one is restricted to present / imperfect subjunctive / pluperfect subjunctive.

Common Mistakes

Key takeaways

• Three conditional types: real (si + present, present/future/imperative), hypothetical (si + imperfect subjunctive, conditional), counterfactual past (si + pluperfect subjunctive, conditional perfect or pluperfect subjunctive).
• Never use the future or the conditional after si in a conditional clause. Si tendría and si vendrá are both wrong.
• The hypothetical is formed with the imperfect subjunctive (tuviera, fuera, supiera) and the conditional (tendría, sería, sabría).
• The counterfactual past uses hubiera/hubiese + participle in the si clause; the main clause can be habría + participle or hubiera + participle — both work, hubiera is slightly more colloquial.
• The -ra and -se forms of the imperfect subjunctive are equivalent in peninsular Spanish. -ra is more frequent; -se is slightly more literary.
• Si = whether (indirect question) has no tense restrictions; the future and the conditional are allowed there.
• After si, ask yourself: real possibility? Hypothetical? Past that didn't happen? Pick the row of the table and follow the pairing — there's no creative freedom in the tense choice.