A causal clause tells you why something happens — it gives the reason, motive, or cause behind the main statement. In English you reach for "because," "since," "as," or "given that"; Portuguese has a parallel set of connectors, and choosing among them depends on how the reason relates to the conversation. This page covers the everyday ones (porque, já que, como) and the more formal ones (visto que, dado que, pois), all of which share one crucial feature: they take the indicative.
The single most important rule: causal clauses take the indicative
A cause is a fact. When you say "I stayed home because it was raining," the rain is real — it actually happened. Portuguese marks real, asserted facts with the indicative mood, so every causal connector is followed by an indicative verb, never a subjunctive.
This is the cleanest way to keep causal clauses apart from purpose clauses. Purpose ("so that you understand," para que você entenda) describes an action that is wished for but not yet real, so it takes the subjunctive. Cause describes something already true, so it takes the indicative. Same English-looking territory, opposite moods.
Fiquei em casa porque estava chovendo.
I stayed home because it was raining.
Não fui à festa porque estava cansado.
I didn't go to the party because I was tired.
Porque — "because" (the workhorse)
Porque is by far the most common causal connector and the default answer to a por que? question. It introduces the direct reason and normally comes after the main clause.
Levei o guarda-chuva porque o céu estava nublado.
I took the umbrella because the sky was cloudy.
— Por que você não comeu? — Porque não estava com fome.
— Why didn't you eat? — Because I wasn't hungry.
A gente chegou atrasado porque o trânsito estava horrível.
We arrived late because the traffic was awful.
The four "porque" spellings — a trap for everyone
This is the single biggest source of written errors, even for native speakers. Portuguese has four distinct forms that sound nearly identical out loud:
| Form | Function | Example |
|---|---|---|
| porque (one word) | because — the causal conjunction (this page) | Fiquei porque chovia. |
| por que (two words) | why — in a direct or indirect question | Por que você chorou? |
| por quê (two words, accented) | why — at the end of a sentence or standing alone | Você não veio, por quê? |
| o porquê (noun) | the reason — a noun, takes an article | Não sei o porquê da briga. |
Já que / uma vez que — "since / seeing that" (a known reason)
Já que and uma vez que present a reason that both speakers already know or that is taken as given. English "since" or "seeing that" captures this perfectly. Because the reason is shared background rather than brand-new information, these clauses very often come first, setting the stage for the main point.
Já que você está aqui, me ajuda a carregar essas caixas.
Since you're here, help me carry these boxes.
Uma vez que ninguém se opõe, vamos seguir com o plano.
Since no one objects, let's go ahead with the plan.
Já que o restaurante estava fechado, acabamos pedindo pizza.
Since the restaurant was closed, we ended up ordering pizza.
The difference from porque is informational, not grammatical. Porque answers a genuine "why?" and delivers new information; já que invokes a reason that's already on the table. Compare: "Por que vamos de táxi?" — "Porque está chovendo" (new info) versus "Já que está chovendo, vamos de táxi" (the rain is established; we draw the consequence).
Como — "since / as" (must come first)
Como can mean "since/as" in a causal sense, but it carries a strict syntactic rule that trips up English speakers: a causal como clause must come at the beginning of the sentence, before the main clause.
Como estava chovendo, fiquei em casa.
Since it was raining, I stayed home.
Como ninguém atendia o telefone, decidi passar lá pessoalmente.
As nobody was answering the phone, I decided to drop by in person.
Como o ônibus não chegava, peguei um aplicativo.
Since the bus wasn't coming, I took a rideshare.
If you move that clause to the end, the meaning collapses — como at the end of a clause is read as "how" or "like," not "since." So "Fiquei em casa como estava chovendo" does not mean "I stayed home since it was raining"; it sounds broken. This positional rule is absolute.
Visto que / dado que — "given that" (formal)
Visto que and dado que mean "given that / in view of the fact that." They belong to formal and academic register — reports, essays, legal language, formal speech — and would sound stiff in casual chat. They typically open the sentence.
Visto que os prazos foram cumpridos, o projeto será aprovado.
Given that the deadlines were met, the project will be approved.
Dado que a demanda aumentou, a empresa contratou mais funcionários.
Given that demand rose, the company hired more staff.
These come from absolute participial constructions (visto = "seen," dado = "given") that have hardened into fixed conjunctions. In this conjunction role they no longer change form and are followed by a normal conjugated indicative verb.
Pois — "for / because" (slightly formal, often written)
Pois introduces a reason or justification and feels a touch more formal or literary than porque. It always follows the main clause and is usually preceded by a comma. You'll see it constantly in writing and careful speech.
Não insista, pois ele já tomou a decisão.
Don't insist, for he has already made his decision.
Vista um casaco, pois lá fora está frio.
Put on a coat, for it's cold outside.
Be careful: pois has other jobs too. Standing alone as pois é it means "yeah / that's right," and pois não is a polite "of course / how can I help you." Those are conversational fillers, not causal connectors — only the comma-introduced pois + clause carries the "because" meaning.
Quick reference
| Connector | Meaning | Register | Typical position |
|---|---|---|---|
| porque | because (new reason) | neutral | after main clause |
| já que / uma vez que | since (known reason) | neutral | usually first |
| como | since / as | neutral | first only |
| pois | for / because | slightly formal, written | after main clause |
| visto que / dado que | given that | formal / academic | usually first |
Common Mistakes
❌ Fiquei em casa por que estava chovendo.
Incorrect — the causal 'because' is one word, porque, not the two-word question form.
✅ Fiquei em casa porque estava chovendo.
I stayed home because it was raining.
❌ Fiquei em casa como estava chovendo.
Incorrect — causal como cannot follow the main clause; it must come first.
✅ Como estava chovendo, fiquei em casa.
Since it was raining, I stayed home.
❌ Estudei muito porque eu passe na prova.
Incorrect — using the subjunctive after a causal connector; cause is a fact and takes the indicative.
✅ Estudei muito porque queria passar na prova.
I studied a lot because I wanted to pass the exam.
❌ Por que você não veio? Por que eu estava doente.
Incorrect — the answer reuses the question's two-word spelling instead of the causal porque.
✅ Por que você não veio? Porque eu estava doente.
Why didn't you come? Because I was sick.
❌ Não sei o por que da confusão.
Incorrect — as a noun meaning 'the reason,' it is the single word o porquê.
✅ Não sei o porquê da confusão.
I don't know the reason for the confusion.
Key Takeaways
- All causal clauses take the indicative — the reason is a real fact, not a wish.
- Porque is the everyday default and answers "why?"; the two-word por que asks the question, accented por quê ends a sentence, and o porquê is the noun "the reason."
- Já que / uma vez que mark a known reason and usually come first; como (causal) is clause-initial only.
- Visto que / dado que are formal "given that"; pois is a slightly formal written "for."
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Start learning Portuguese→Related Topics
- Purpose Clauses (Para Que, A Fim de Que)B1 — How to express goals and intentions — para + infinitive for shared subjects, para que + subjunctive for different subjects, and the formal a fim de variants.
- Interrogative Onde, Aonde, Quando, Como, Por queA1 — The remaining question words in Brazilian Portuguese — where, when, how, why — including onde vs aonde and the por que / por quê / porque / porquê spelling quartet.
- Causal Conjunctions (Porque, Já Que)A2 — How porque, pois, como, já que and visto que introduce a cause — all with the indicative, because a cause is asserted as real.
- Indicative vs Subjunctive: Decision GuideB1 — A practical guide to choosing the indicative or subjunctive in Portuguese using the assertion test, trigger lists, and the negation flip with verbs like achar.