Si is not the only way to express a conditional idea in Spanish. A whole family of conjunctions — a menos que, salvo que, a no ser que, en caso de que, con tal de que, siempre que, siempre y cuando, mientras, como — covers conditional territory with sharper or more specialised meanings. Some are negative ("unless"); some are restrictive ("provided that"); some toggle between conditional and habitual readings depending on mood. This page is the reference for all of them: what they mean, which mood they take, and the traps each one sets.
The unifying generalisation is simple: when these conjunctions express a conditional, hypothetical, or yet-to-be-fulfilled idea, they take the subjunctive. When they express a habitual, real, or factual idea (only some of them allow this), they take the indicative.
A menos que, salvo que, a no ser que — "unless"
Three near-synonyms for English unless. All three take the subjunctive without exception. The condition they introduce is by definition unrealised — they negate the condition under which the main event would not happen — so the mood is locked in.
| Conjunction | Register | Note |
|---|---|---|
| a menos que | neutral, most common in Spain | everyday + written |
| salvo que | slightly more formal | journalism, business |
| a no ser que | colloquial, peninsular-flavoured | spoken Spanish in Spain |
No iré a la fiesta a menos que vengas tú también.
I won't go to the party unless you come too.
El vuelo saldrá puntual, salvo que haya problemas con la torre de control.
The flight will leave on time, unless there are problems with the control tower.
No se lo diría a nadie, a no ser que me lo pidieras.
I wouldn't tell anyone, unless you asked me to.
The three are largely interchangeable in modern Spanish, with the register differences shown above. In peninsular speech, a no ser que feels especially native and slightly more casual than a menos que.
En caso de que — "in case", "in the event that"
Always subjunctive. Introduces a hypothetical contingency you want to prepare for. The condition is by definition unrealised at the moment of speaking.
Llévate paraguas en caso de que llueva esta tarde.
Take an umbrella in case it rains this afternoon.
Te dejo mi número en caso de que necesites contactarme.
I'll leave you my number in case you need to contact me.
En caso de que el ascensor se quede parado, llamad a recepción.
In the event that the lift gets stuck, call reception.
When the subject of en caso de que matches the main-clause subject, peninsular Spanish often compresses to en caso de + infinitive:
En caso de detectar humo, evacúen el edificio por las escaleras.
If smoke is detected, evacuate the building via the stairs.
This compressed form is everywhere on emergency signs and in formal instructions. Note the absence of que and the bare infinitive — same logic as the de + infinitive construction.
Con tal de que — "as long as", "provided that"
Subjunctive. Expresses a condition the speaker is willing to accept in exchange for something. There's always an implicit transactional flavour: "I'll do X provided Y".
Hago lo que sea con tal de que me dejes en paz.
I'll do whatever, as long as you leave me alone.
Te presta el coche con tal de que se lo devuelvas con el depósito lleno.
He'll lend you the car provided you return it with a full tank.
Mis padres me dejan salir con tal de que llegue antes de la una.
My parents let me go out as long as I'm home before one.
When the two clauses share a subject, you can drop the que and use the infinitive: con tal de + infinitive.
Hago lo que sea con tal de aprobar el examen.
I'll do anything to pass the exam.
Conduce despacio con tal de no asustar a los niños.
He drives slowly so as not to scare the kids.
The infinitive variant slides toward a purpose reading ("so as to") and is more common in everyday speech.
Siempre que, siempre y cuando — "as long as", "whenever"
These are the trickiest because siempre que has two readings that the mood disambiguates.
- Conditional ("provided that") → subjunctive.
- Habitual / temporal ("every time that, whenever") → indicative.
Te ayudo siempre que me lo pidas educadamente.
I'll help you as long as you ask me politely. (conditional → subjunctive)
Te ayudaba siempre que me lo pedías.
I used to help you whenever you asked. (habitual → indicative)
Same conjunction, two different meanings — and the only way to tell them apart is the mood. The subjunctive marks "provided that" (the condition may or may not be met); the indicative marks "every time that" (the events did/do happen).
- subjunctive = "provided that". Siempre que
- indicative = "every time that". This is the single most useful disambiguation in the conjunction family — internalise it.
A few more examples to drill the contrast:
Puedes coger el coche siempre que tengas cuidado.
You can take the car as long as you're careful. (conditional → subj.)
Cogía el coche siempre que tenía un examen.
He'd take the car whenever he had an exam. (habitual → ind.)
Te invitaré siempre que vengas tú también.
I'll invite you as long as you come too. (conditional → subj.)
Te invitaba siempre que venías tú también.
I used to invite you whenever you came too. (habitual → ind.)
Siempre y cuando does not have the habitual reading — it is conditional-only and always takes the subjunctive. If you want to write unambiguously "as long as", siempre y cuando is the safer choice.
Te dejo el portátil siempre y cuando lo cuides bien.
I'll lend you the laptop, as long as you take good care of it.
El descuento es válido siempre y cuando se pague antes del viernes.
The discount is valid provided you pay before Friday.
Mientras (and mientras que) — "as long as"
Like siempre que, mientras has two readings.
- Conditional ("as long as") → subjunctive.
- Temporal / simultaneous ("while") → indicative.
Mientras no llueva, podemos seguir andando.
As long as it doesn't rain, we can keep walking. (conditional → subj.)
Mientras andábamos, empezó a llover.
While we were walking, it started to rain. (temporal → ind.)
Mientras tengas paciencia, lo conseguirás.
As long as you have patience, you'll get there.
The conditional reading often appears with a negative inside the clause (mientras no...), which is a strong cue: "as long as not" makes no temporal sense, so it must be conditional.
A subtle peninsular distinction: mientras que (with que) is mostly used in modern Spanish for contrast — "whereas", not "while" or "as long as". Mi hermano estudia derecho, mientras que yo estudio medicina — "My brother studies law, whereas I study medicine." Don't confuse it with mientras; in conditional contexts, drop the que.
Como + subjunctive — the peninsular threat-conditional
This is a peninsular specialty worth flagging. Como normally introduces a manner ("how") or a cause ("since/because"); but when followed by the subjunctive, it acts as a strong, often threatening si-conditional.
Como vuelvas a llegar tarde, te quedas sin postre.
If you come home late again, no dessert for you.
Como no me pagues lo que me debes, te denuncio.
If you don't pay me what you owe, I'll take you to court.
Como se entere mi madre, me mata.
If my mother finds out, she'll kill me.
Como + subjunctive is colourful, colloquial, and emphatic. It packs a warning — the consequence is presented as inevitable. It's a defining flavour of peninsular spoken Spanish; Latin American varieties prefer si. Note: it is subjunctive-only in this conditional reading. Como vuelves a llegar tarde (with indicative) is read as a cause: "since you're coming home late again."
Subject and word order
These conjunction-clauses can sit either before or after the main clause, and the subject is overt whenever it would be in any subordinate clause. There is no general restriction on subject position inside them.
A menos que vengas tú, no iré.
Unless you come, I won't go. (clause first)
No iré a menos que vengas tú.
I won't go unless you come. (clause second)
Both orders are natural; the choice tracks information structure (what's already known vs. new).
A quick-reference table
| Conjunction | Meaning | Mood | Register |
|---|---|---|---|
| a menos que | unless | subjunctive | neutral |
| salvo que | unless / except if | subjunctive | slightly formal |
| a no ser que | unless | subjunctive | colloquial peninsular |
| en caso de que | in case, in the event that | subjunctive | neutral + formal signage |
en caso de
| in case (same subject) | infinitive | formal / instructional |
| con tal de que | as long as, provided that | subjunctive | neutral |
con tal de
| so as to, as long as (same subject) | infinitive | everyday |
| siempre que (conditional) | as long as | subjunctive | neutral |
| siempre que (habitual) | whenever, every time that | indicative | neutral |
| siempre y cuando | as long as (conditional only) | subjunctive | neutral, unambiguous |
| mientras (conditional) | as long as | subjunctive | neutral |
| mientras (temporal) | while | indicative | neutral |
| como (threat-conditional) | if (with warning) | subjunctive | colloquial peninsular |
Stacking and chaining
These conjunctions can be stacked or chained, especially in legal and contractual prose:
Te ayudo siempre y cuando me lo pidas con tiempo y en caso de que no esté de viaje.
I'll help you as long as you ask me in advance and provided I'm not travelling.
El contrato se renovará automáticamente, salvo que una de las partes notifique lo contrario por escrito con un mes de antelación.
The contract will renew automatically, unless one of the parties notifies otherwise in writing one month in advance.
The subjunctive applies to every conditional conjunction in the chain.
Common Mistakes
❌ No iré a menos que vienes tú.
Wrong — a menos que is followed by the subjunctive, not the indicative.
✅ No iré a menos que vengas tú.
I won't go unless you come.
❌ Llévate paraguas en caso de que llueve.
Wrong — en caso de que takes subjunctive without exception.
✅ Llévate paraguas en caso de que llueva.
Take an umbrella in case it rains.
❌ Te ayudo siempre que me lo pides educadamente.
Wrong reading — with indicative this means 'every time you ask me politely (you do, habitually)'. For 'provided that', the subjunctive is required.
✅ Te ayudo siempre que me lo pidas educadamente.
I'll help you as long as you ask me politely.
❌ Mientras no llueve, podemos seguir andando.
Wrong — the conditional reading of 'mientras' ('as long as') requires the subjunctive.
✅ Mientras no llueva, podemos seguir andando.
As long as it doesn't rain, we can keep walking.
❌ Como vuelves a llegar tarde, te quedas sin postre.
With indicative this is read as a cause: 'since you're coming late again, no dessert.' For the conditional threat reading, switch to subjunctive.
✅ Como vuelvas a llegar tarde, te quedas sin postre.
If you come home late again, no dessert for you.
Key takeaways
- The "unless" family (a menos que, salvo que, a no ser que) always takes the subjunctive.
- En caso de que and con tal de que always take the subjunctive; their de + infinitive shortcuts apply when the subject matches the main clause.
- Siempre que and mientras toggle between conditional (subjunctive) and habitual/temporal (indicative). The mood disambiguates.
- Siempre y cuando is conditional-only — use it for unambiguous "as long as" in writing.
- Como
- subjunctive is a peninsular threat-conditional: vivid, colloquial, and always with a warning.
- Cross-reference: for the full subjunctive trigger inventory, see verbs / subjunctive / triggers complete.
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Start learning Spanish→Related Topics
- Condicionales mixtosB2 — Mixed conditionals combine a past hypothetical with a present consequence, or a present trait with a past outcome — built by matching each clause's tense to the time it lives in, not by fixed pairings.
- Como si: estructura comparativa hipotéticaB1 — Como si ('as if') compares a real situation to a hypothetical one, and always forces the imperfect or pluperfect subjunctive — never the indicative, never the present subjunctive.
- De + infinitivo: condicional alternativoB2 — A formal alternative to si-clauses: 'de + infinitive' compresses the conditional protasis into a non-finite phrase — concise, written-register, and beloved of journalism and oratory.
- Disparadores del subjuntivo: lista exhaustivaB2 — An exhaustive reference of every subjunctive trigger in peninsular Spanish, grouped by category and annotated with the indicative/subjunctive alternations they participate in.
- Polaridad y subjuntivo: el efecto de la negaciónC1 — How negation, questions and polarity systematically flip the mood of subordinate clauses — the deep logic behind the creer/no creer puzzle.
- Subjuntivo coordinado: quiero que vengas y que traigas el libroC1 — When two or more subordinate clauses depend on a single trigger, Spanish coordinates them with 'y que', 'o que', 'ni que' — and the mood must hold consistently across the whole coordinated structure.