Causal conjunctions answer the question "why?" — they link a clause stating a cause or reason to the clause it explains. The single most important fact about them in Portuguese is that they all take the indicative, never the subjunctive. This page shows you the main causal conjunctions, the rules for placement, and why the mood is fixed.
Why causal conjunctions always take the indicative
When you give a reason, you are presenting it as a fact — something that is true and that you are asserting. The subjunctive in Portuguese marks the opposite: doubt, wishes, possibilities, things that are not (yet) real. A cause, by definition, is real enough to produce an effect, so it lives squarely in the indicative.
This is the underlying logic that lets you predict the mood without memorizing a list: if the clause asserts something that actually happened or is happening, use the indicative. Compare this with purpose clauses (para que + subjunctive), where the goal has not yet happened — that contrast is the heart of why causal and final conjunctions behave so differently.
porque — the everyday "because"
Porque (written as one word, no accent) is the default causal conjunction and the one you will use most. It introduces the reason and almost always follows the main clause.
Não fui trabalhar porque estava com febre.
I didn't go to work because I had a fever.
A gente saiu mais cedo porque o trânsito estava horrível.
We left earlier because the traffic was terrible.
English uses one spelling, "because," for the conjunction. Portuguese has a notorious set of look-alikes you must keep apart in writing:
| Form | Use | Example |
|---|---|---|
| porque | conjunction "because" (answer) | Fiquei em casa porque chovia. |
| por que | "why" in questions (two words) | Por que você não veio? |
| porquê | noun "the reason" (with article) | Não sei o porquê disso. |
| por quê | "why" at end of sentence / before punctuation | Você não veio por quê? |
Por que você está rindo? — Porque a sua cara tá engraçada.
Why are you laughing? — Because your face is funny.
pois — "for / since" (slightly more formal)
Pois introduces a cause and reads as a touch more formal or literary than porque. It always comes after the clause it explains and is typically set off by a comma.
Vamos ter que remarcar, pois o palestrante adoeceu.
We'll have to reschedule, since the speaker fell ill.
Ele não respondeu, pois ainda não tinha lido a mensagem.
He didn't answer, for he hadn't read the message yet.
como — "since," but only at the start of a sentence
Como can mean "since / because," but with a crucial restriction: in this causal sense it works only sentence-initially, before the main clause. The cause comes first, then the consequence.
Como estava tarde, fomos embora.
Since it was late, we left.
Como ninguém respondeu, cancelei a reunião.
Since nobody answered, I cancelled the meeting.
If you move como to the end of the sentence, it stops being causal and becomes manner or comparison ("as / how / like"):
Faça como eu mostrei.
Do it the way I showed you.
So position is meaning: front-of-sentence como = cause; mid- or end-of-sentence como = manner. There is no way to say "...because..." with como after the main clause — use porque instead.
já que / uma vez que / visto que — "since / given that"
These three present the cause as already known or shared information — the reason is taken for granted, and the speaker builds an argument on it. They are flexible in position and all take the indicative.
Já que você insiste, eu aceito o convite.
Since you insist, I'll accept the invitation.
Uma vez que o contrato já foi assinado, não dá para voltar atrás.
Given that the contract has already been signed, there's no going back.
Visto que os dados confirmam a hipótese, prosseguimos com o estudo.
Given that the data confirm the hypothesis, we proceed with the study.
Register notes: já que is neutral and very common in speech. Uma vez que is slightly more formal. Visto que is (formal) / (academic) and frequent in written reasoning. Porquanto is (archaic) / (literary) — you will meet it in old texts and legal prose, but no Brazilian says it in conversation.
Porquanto o réu confessou, o juiz proferiu a sentença.
Inasmuch as the defendant confessed, the judge handed down the sentence. (archaic/legal)
Don't confuse causal porque with purpose para que
This is the single most damaging error English speakers make, because English blurs the two with "so." Look at the contrast:
Saí cedo porque havia muito trânsito.
I left early because there was a lot of traffic. (cause — indicative)
Saí cedo para que não houvesse problema com o trânsito.
I left early so that there wouldn't be a problem with the traffic. (purpose — subjunctive)
Porque + indicative explains a real cause that already exists. Para que + subjunctive states a goal that has not happened yet. If you can replace "because" with "for the reason that," it's causal; if you can replace it with "in order that," it's purpose.
Common Mistakes
❌ Não vim por que estava doente.
Incorrect — 'por que' (two words) is for questions; the conjunction is one word.
✅ Não vim porque estava doente.
I didn't come because I was sick.
❌ Fomos embora como estava tarde.
Incorrect — causal 'como' must be sentence-initial; here it reads as manner.
✅ Como estava tarde, fomos embora.
Since it was late, we left.
❌ Aceito já que você insista.
Incorrect — causal conjunctions take the indicative, not the subjunctive.
✅ Aceito já que você insiste.
I accept since you insist.
❌ Estudei muito porque passe na prova.
Incorrect — this is a purpose, so you need 'para que' + subjunctive, not 'porque'.
✅ Estudei muito para que eu passasse na prova.
I studied a lot so that I would pass the exam.
Key Takeaways
- All causal conjunctions take the indicative, because a cause is asserted as real.
Porque(one word) is the everyday "because"; keep it apart frompor que,porquê, andpor quê.- Causal
comoworks only at the start of a sentence; elsewhere it means "as / like." Já que,uma vez que,visto quepresent the cause as known information; register rises from neutral to (formal)/(academic) across that list, withporquantobeing (archaic).- Never swap causal
porque(indicative) for purposepara que(subjunctive) just because English uses "so" for both.
Now practice Portuguese
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Portuguese→Related Topics
- Conjunctions and Mood SelectionB1 — The master table mapping each Brazilian Portuguese conjunction to the mood it governs — indicative, subjunctive, or future subjunctive — and the assertion principle that predicts them all.
- Cause-Effect Markers (Por Isso, Portanto)B1 — The two sides of causal linking in Brazilian Portuguese — cause connectors like 'porque' and 'já que' versus effect connectors like 'por isso' and 'portanto' — sorted by register.
- Adverbial ClausesB1 — How Brazilian Portuguese builds time, cause, condition, concession, purpose, result and comparison clauses — and why each conjunction picks the indicative or the subjunctive.
- Purpose Conjunctions (Para Que, A Fim de Que)B1 — How para que and a fim de que express purpose with the subjunctive, when to switch to para + infinitive, and how de modo que splits between purpose and result.
- The Subjunctive in BR Portuguese: OverviewA2 — What the subjunctive is, why Brazilian Portuguese keeps all three of its tenses fully alive, and what triggers it.