Si is not the only way to introduce a condition in Spanish. A whole family of conjunctions can take its place, each one adding its own flavor — exception, exchange, precaution, minimum requirement. They all share one crucial property: every one of them requires the subjunctive. There are no indicative conditions hiding in this list.
A menos que (unless)
A menos que introduces the one case where the main clause won't apply. English "unless" is the closest match.
No puedo ayudarte a menos que me digas la verdad.
I can't help you unless you tell me the truth.
A no ser que means exactly the same thing and is fully interchangeable. It shows up slightly more often in writing and slightly less in casual speech, but either one is always safe.
Con tal de que (as long as, provided that)
Con tal de que introduces a condition the speaker is willing to accept in exchange for the main clause. It feels like a trade.
Te presto el carro con tal de que lo devuelvas con el tanque lleno.
I'll lend you the car as long as you return it with a full tank.
Haré lo que sea con tal de que seas feliz.
I'll do whatever it takes provided that you're happy.
A condición de que is a more formal cousin with the same meaning. You will see it in contracts, legal writing, and polite letters.
Firmaré el contrato a condición de que se incluya la cláusula de confidencialidad.
I'll sign the contract on the condition that the confidentiality clause is included.
En caso de que (in case)
En caso de que introduces a precaution — a possibility the speaker is preparing for, whether or not it actually happens.
Lleva un paraguas en caso de que llueva.
Take an umbrella in case it rains.
Aquí tienes mi número, en caso de que necesites algo.
Here's my number, in case you need anything.
You can also drop que and use en caso de + infinitive for a slightly more compact version, similar to the de + infinitive conditional: en caso de necesitar algo. Both versions are grammatical and common.
Siempre y cuando (as long as)
Siempre y cuando sets a minimum requirement. The speaker is willing to commit, but only if the condition holds steadily.
Puedes salir con tus amigos siempre y cuando regreses antes de las diez.
You can go out with your friends as long as you come back before ten.
El tratamiento funciona siempre y cuando lo sigas al pie de la letra.
The treatment works as long as you follow it to the letter.
Siempre y cuando is slightly more emphatic than con tal de que — it suggests the condition must hold throughout, not just once at the start.
Quick summary
| Expression | English | Flavor |
|---|---|---|
| a menos que | unless | exception |
| a no ser que | unless | exception (formal) |
| con tal de que | as long as | willing exchange |
| a condición de que | on the condition that | formal exchange |
| en caso de que | in case | precaution |
| siempre y cuando | as long as | ongoing requirement |
The subjunctive is not optional
Every single expression on this list forces the verb that follows into the subjunctive, and this rule does not bend. It applies regardless of the main verb, the tense, or the speaker's attitude. The mood is locked in by the conjunction itself.
Te ayudaré con tal de que me escuches.
I'll help you as long as you listen to me.
Past contexts
When the main clause is in the past, these conjunctions still take the subjunctive — but now the imperfect subjunctive instead of the present. The sequence of tenses pulls everything backward together.
Me dijo que iría al concierto con tal de que lo acompañara.
He told me he would go to the concert as long as I went with him.
Salimos temprano en caso de que hubiera tráfico.
We left early in case there was traffic.
The core rule holds: conditional conjunctions always demand the subjunctive. The only thing that changes is which subjunctive tense fits the timeline.
Related Topics
- Type 1: ProbableB1 — Use a present-tense si-clause with a future, imperative, or present result clause for situations that are likely to happen.
- Type 2: ImprobableB2 — Pair an imperfect-subjunctive si-clause with a conditional result clause for hypothetical or unlikely present situations.
- De + Infinitive ConditionalB2 — An alternative to si-clauses: de followed by an infinitive expresses the same condition in a more formal or literary register.