Conditional Conjunctions (Caso, Desde Que, A Menos Que)

Portuguese has a whole family of conjunctions that introduce conditional clauses without using se. These conjunctions let you say things like "provided that," "unless," "in case," and "as long as" — each with its own shade of meaning, its own register, and, crucially, its own tense requirement. Unlike se (which takes the future subjunctive for open conditions), most of these conjunctions trigger the present subjunctive. Getting this right is the mark of a B2+ speaker.

A note on the URL: This page uses a legacy slug containing "si-" for compatibility. Portuguese uses se throughout.

Why these conjunctions exist

Se is the workhorse of Portuguese conditionals, but it is neutral — it sets up a condition without adding any pragmatic color. The other conjunctions each carry extra meaning:

• caso — a slightly more formal, cautious "if" ("in case")
• desde que — conditional with a flavor of permission ("provided that")
• contanto que — condition as a limit ("as long as")
• a menos que / a não ser que — negative conditional ("unless")
• salvo se — legalistic "except if"

These conjunctions let you be more precise than se allows. A native speaker who wants to grant conditional permission will say desde que, not se — and a learner who only uses se sounds less fluent.

The key rule: present subjunctive, not future subjunctive

Here is the single most important grammatical fact on this page:

Most of these conjunctions take the PRESENT subjunctive, not the future subjunctive.

This is different from se. With se, open conditions require the future subjunctive (se eu puder, "if I can"). With caso, desde que, contanto que, a menos que, and a não ser que, you use the present subjunctive (caso eu possa, "in case I can").

Both sentences say essentially the same thing — the difference is the conjunction and therefore the required tense. Never put the future subjunctive after caso or desde que. That error marks you as a learner.

One exception: salvo se ("except if") behaves like se and takes the future subjunctive. More on this below.

Caso — the formal "if"

Caso means "in case" or "if," with a slightly more formal or cautious tone than se. It comes from the noun caso (a case, a situation) and treats the condition as one possible scenario to plan for.

Notice two things. First, chegues, haja, seja, chova are all present subjunctive forms. Second, caso can be placed at the beginning of the sentence or after the main clause (the caso chova example at the end shows this).

Caso vs. se

Caso is interchangeable with se in many open-conditional contexts, but it has a slightly different flavor:

• Caso sounds more formal, more careful, slightly bureaucratic.
• Caso often implies "on the off chance that" rather than "if."
• Caso is more common in writing than in casual speech.

The second sentence implies that you are planning for a possibility. The first simply reacts if it happens.

Desde que — "provided that"

Desde que has two meanings, distinguished by context and mood:

1. With subjunctive: "provided that" — a conditional with the flavor of permission or requirement.
2. With indicative: "since" — a temporal conjunction indicating duration from a past point.

We focus on the first meaning here. Desde que + present subjunctive sets up a condition that, if met, allows the main clause to happen.

Note how desde que typically introduces a requirement from the speaker's side — it is the language of conditional consent.

Desde que (conditional) vs. desde que (temporal)

The same two words mean very different things depending on the mood that follows:

The mood disambiguates. When native speakers hear desde que + present subjunctive, they interpret it conditionally. When they hear desde que + preterite or imperfect indicative, they interpret it temporally.

Contanto que — "as long as"

Contanto que is similar to desde que with the subjunctive meaning, but slightly more formal and with a stronger flavor of "strictly on the condition that." It is almost archaic in some contexts but still appears in contracts, instructions, and formal prose.

In everyday speech, desde que is more common than contanto que. But contanto que appears in writing and in somewhat formal spoken Portuguese.

A menos que — "unless"

A menos que is the standard Portuguese expression for "unless." It takes the present subjunctive and effectively negates the condition: X happens unless Y happens = X happens if not-Y.

Note: a menos que already contains a negative implication, so avoid a double negative inside the clause (see Common Mistakes below).

A não ser que — "unless" (colloquial variant)

A não ser que means exactly the same as a menos que — "unless" — but it is the more common form in everyday European Portuguese. Many speakers use it habitually and rarely reach for a menos que.

Both a menos que and a não ser que are interchangeable and both take the present subjunctive. A não ser que feels slightly more colloquial and flows more naturally in conversation.

Salvo se — "except if" (legalistic)

Salvo se means "except if" and is heavily associated with legal, contractual, and bureaucratic language. Unlike all the other conjunctions on this page, salvo se behaves like regular se: it takes the future subjunctive when the condition is future, not the present subjunctive.

Salvo se is essentially se with an "except" flavor, so it takes the same tenses as se.

Related: exceto se, excepto se, a não ser se

These variants all mean "except if" and behave like salvo se — they take the same tense as se (future subjunctive for open conditions).

Note: in the 1990 Portuguese spelling agreement, excepto became exceto (losing the silent p). Both spellings appear in older texts, but modern European Portuguese prefers exceto.

Summary table of conjunctions

Combining with main-clause tenses

The main clause after these conjunctions behaves just as in se-conditionals — present indicative, future indicative, imperative, or even conditional forms can appear:

Which conjunction to choose?

• se — default, neutral "if"
• caso — "in case" or slightly formal "if"; emphasizes planning
• desde que / contanto que — "provided that"; emphasizes the condition as a requirement
• a menos que / a não ser que — "unless"; negates the condition
• salvo se / exceto se — "except if"; formal exception-making

Your choice signals register, attitude, and nuance. A lease contract will have caso, desde que, and salvo se. A casual conversation will have se and a não ser que. Academic writing mixes all of them.

Variation: compound conditionals with these conjunctions

These conjunctions can all embed in compound structures. You can combine them with past subjunctive forms for counterfactuals:

The conjunction still forces a subjunctive mood in the subordinate clause — only the aspect/tense shifts based on the counterfactual structure.

Contrast with English "if"

English uses "if" for almost everything and relies on additional words for the nuances: "provided that," "as long as," "unless," "in case," "except if." Portuguese has dedicated conjunctions for each shade. When translating, don't default to se — choose the conjunction that matches the English nuance.

Common Mistakes

Key Takeaways

• These conjunctions replace or complement se with richer nuances: caso, desde que, contanto que, a menos que, a não ser que, salvo se.
• Most take the present subjunctive — not the future subjunctive.
• Exception: salvo se, exceto se behave like se and take the future subjunctive for open conditions.
• Desde que is ambiguous without context: subjunctive = "provided that," indicative = "since (temporal)."
• A menos que and a não ser que are synonymous; the latter is more colloquial.
• Do not double-negate inside a menos que — the conjunction already carries the negation.
• Choose the conjunction that matches the nuance of the English, not just the default "if."