A causal clause (oração causal) answers the question why? by giving the reason for something. "I stayed home because I was tired." "Since it was late, we left." Portuguese has a rich vocabulary of causal connectors — porque, como, já que, visto que, uma vez que, dado que, posto que, pois — each with its own register, position rules, and pragmatic flavour.
All Portuguese causal conjunctions take the indicative. The reason is simple: a cause is a fact being presented as the explanation for another fact. The subjunctive belongs to doubt, wish, and hypothesis — not to stated reasons.
Beyond that, this page also sorts out one of the messiest orthographic traps in Portuguese: the four-way distinction between porque, por que, por quê, and porquê. Get these wrong and your writing screams learner.
The single most important rule
All causal conjunctions in Portuguese take the indicative. Always. Every tense of the indicative is possible, but never the subjunctive.
Fiquei em casa porque estava cansado.
I stayed home because I was tired.
Como estava a chover, levei o guarda-chuva.
Since it was raining, I took the umbrella.
Compare with the subjunctive-triggering concessive embora:
Embora estivesse cansado, fui à festa.
Although I was tired, I went to the party. (concessive — subjunctive)
Fui à festa porque estava cansado e queria distrair-me.
I went to the party because I was tired and wanted to distract myself. (causal — indicative)
Porque — the everyday because
Porque is the default, universal connector for reason. It is the Portuguese equivalent of English because, used in conversation and in formal writing alike.
Não fui trabalhar porque estava doente.
I didn't go to work because I was sick.
Ele saiu cedo porque tinha uma reunião.
He left early because he had a meeting.
Gosto de Lisboa porque é uma cidade luminosa.
I like Lisbon because it's a luminous city.
Estou a aprender português porque vou viver em Coimbra.
I'm learning Portuguese because I'm going to live in Coimbra.
Position: after the main clause (default)
Porque typically follows the main clause. It rarely starts a sentence in formal writing — for that, use como (see below).
Não respondi porque não sabia a resposta.
I didn't answer because I didn't know the answer.
Capitalization: lowercase in the middle of a sentence
Because porque is a subordinating conjunction, it is not capitalized when it appears mid-sentence. This seems obvious, but many learners (especially Spanish speakers accustomed to writing Porque after a pause) get it wrong.
✅ Fui-me embora porque já era tarde.
I left because it was already late.
❌ Fui-me embora Porque já era tarde.
Incorrect — porque is never capitalized mid-sentence.
Standalone porque — answering a question
When answering "Why?" (Porquê?) in conversation, you typically start your reply with Porque...:
— Porque não vieste ontem? — Porque tive de trabalhar.
— Why didn't you come yesterday? — Because I had to work.
Porque vs por que vs porquê vs por quê
This four-way distinction is where even educated native speakers occasionally hesitate. Nail it once and you'll never confuse them again.
| Form | Function | Where it appears | Example |
|---|---|---|---|
| porque | causal conjunction (because) | introduces a subordinate causal clause | Fiquei porque estava cansado. |
| por que | preposition por + relative/interrogative que | in interrogatives (For what reason?) or in relative clauses (for which) | Por que razão não vieste? / A razão por que saí... |
| porquê | noun (the why, the reason) or stressed interrogative at sentence end | with an article, or at the very end of a question | Ninguém sabe o porquê. / Fizeste isso porquê? |
| por quê | preposition por + stressed interrogative quê at end of question | rare in EP; before a pause or at clause end | Estás a rir por quê? (less common in EP) |
Practical rules for European Portuguese
Subordinating conjunction (because) → porque (one word, no accent).
Não vim porque estava doente.
I didn't come because I was sick.
Question at the start → Porque or Por que razão (formal). In European Portuguese, "Porque é que..." with the é que emphasis is extremely common in speech:
Porque é que não vieste?
Why didn't you come? (EP colloquial standard)
Por que razão não vieste?
For what reason didn't you come? (formal)
Question at the end, stressed → porquê (accented):
Não vieste porquê?
Why didn't you come? (emphatic, end-placed)
Fizeste isso porquê?
You did that why?
Noun (the reason, the why) → porquê with article:
Ninguém sabe o porquê da sua ausência.
Nobody knows the reason for his absence.
Há sempre um porquê por detrás de cada gesto.
There's always a reason behind every gesture.
Relative por que (formal, often after a noun of reason):
O motivo por que me calei foi simples.
The reason why I kept quiet was simple.
Como — since, as (initial position)
Como as a causal conjunction means "since, as" and almost always appears at the start of a sentence, introducing the cause first. When como is used this way, the main clause follows.
Como estava a chover, ficámos em casa.
Since it was raining, we stayed home.
Como ninguém respondeu, saí.
As no one answered, I left.
Como não tinha dinheiro, pedi emprestado.
Since I didn't have money, I borrowed some.
Como ele se atrasou, perdemos o comboio.
Since he was late, we missed the train.
Como used this way is a stylistic favourite in writing — it creates a smooth flow where the cause sets the stage and the consequence lands naturally.
Como vs porque
Both mean "because/since", but:
- Porque typically gives new or previously unknown information: "because..." (answering why?).
- Como typically presents background or already-known information: "given that...".
Fiquei em casa porque estava doente.
I stayed home because I was sick. (reason revealed)
Como estava doente, fiquei em casa.
Since I was sick, I stayed home. (context set first)
Como in other roles
Don't confuse causal como with:
- Como meaning how (Como é que sabes? — How do you know?)
- Como meaning like/as in comparisons (Ele é alto como o pai — He's tall like his father)
- Como as the verb "I eat" (eu como)
Context always disambiguates in practice.
Já que — since, given that
Já que presents the cause as information shared between speaker and listener, often as the premise for a suggestion or request. It is distinctly colloquial and friendly.
Já que estás aqui, podes ajudar-me?
Since you're here, can you help me?
Já que insistes, aceito.
Since you insist, I accept.
Já que ninguém quer vir, vou sozinho.
Since no one wants to come, I'll go alone.
Já que falas português, diz-me como se diz isto.
Since you speak Portuguese, tell me how to say this.
The pragmatic effect of já que is often "given that X is the case, it makes sense that Y". It sets up a logical consequence more than a causal explanation.
Visto que, uma vez que — given that, seeing as
Visto que and uma vez que are formal-register equivalents of já que. They are common in essays, news writing, and official language.
Visto que ninguém se opôs, a proposta foi aprovada.
Given that no one objected, the proposal was approved.
Uma vez que as condições foram aceites, avançamos com o projeto.
Since the conditions were accepted, we're moving forward with the project.
Visto que o tempo está bom, podemos fazer o almoço no jardim.
Seeing as the weather is nice, we can have lunch in the garden.
Uma vez que estamos todos reunidos, vamos começar.
Since we're all gathered, let's begin.
Uma vez que also has a temporal reading ("once that"), but context usually makes the causal sense clear.
Dado que, posto que — formal/academic
Dado que (literally "given that") and posto que (a more literary "since") belong to formal written Portuguese.
Dado que o problema persiste, temos de agir.
Given that the problem persists, we have to act.
Dado que não recebemos resposta, cancelámos a reunião.
Given that we didn't receive a reply, we cancelled the meeting.
Posto que nada mais havia a dizer, despediu-se.
Since there was nothing more to say, he said goodbye. (literary)
Posto que is archaic/literary in modern European Portuguese; most speakers would use uma vez que or já que instead. Note also that in older Portuguese (and still in Brazilian Portuguese), posto que was used as a concessive ("although") — a usage that survives mainly in legal texts.
Pois — the spoken explanatory connector
Pois is a chameleon word: it can mean "yes, indeed", "because", "well", or "so" depending on context. As a causal connector, it is close to porque but more colloquial and often mid-sentence, separated by a comma.
Não vou sair, pois está a chover.
I'm not going out, because it's raining.
Temos de nos despachar, pois o comboio parte dentro de dez minutos.
We have to hurry, because the train leaves in ten minutes.
In speech, pois also functions as a discourse particle ("yeah, right"), which is unrelated to the causal use.
Por + noun and por + infinitive — because of
Portuguese also expresses cause with the preposition por + a noun or an infinitive, rather than with a full clause.
Por + noun
Chegou atrasado por causa do trânsito.
He arrived late because of the traffic.
Foi suspenso por mau comportamento.
He was suspended for bad behaviour.
Por + infinitive
Foi castigado por ter mentido.
He was punished for having lied.
Por teres chegado tarde, perdeste o início.
Because you arrived late, you missed the beginning. (personal infinitive)
Por causa de (neutral), devido a (formal)
Cancelaram o voo devido ao mau tempo.
They cancelled the flight due to bad weather. (formal)
Não dormi por causa do barulho.
I didn't sleep because of the noise. (everyday)
Full summary table
| Connector | Meaning | Register | Typical position | Mood |
|---|---|---|---|---|
| porque | because | neutral | after main clause | indicative |
| como | since, as | neutral/written | sentence-initial | indicative |
| já que | since, given that | colloquial | either position | indicative |
| visto que | seeing as | formal | either position | indicative |
| uma vez que | since, given that | formal | either position | indicative |
| dado que | given that | formal / academic | sentence-initial | indicative |
| posto que | since (archaic) | literary / legal | sentence-initial | indicative |
| pois | because (colloquial) | spoken | after main clause, with comma | indicative |
| por + inf / por causa de / devido a | because of / due to | varies | prepositional phrase | — |
Purpose vs cause: a sharp distinction
English speakers sometimes blur "why" meaning goal with "why" meaning reason. Portuguese does not.
- Cause (reason — past-oriented): porque, como, já que
- indicative.
- Purpose (goal — future-oriented): para (que), a fim de (que)
- infinitive or subjunctive.
Estudei muito porque tinha um exame difícil.
I studied hard because I had a difficult exam. (reason)
Estudei muito para passar no exame.
I studied hard (in order) to pass the exam. (goal)
Same English "why", two entirely different Portuguese constructions. See complex/purpose-clauses for the full treatment.
Register ladder
| Register | Preferred connector |
|---|---|
| Casual speech | porque, pois, já que |
| Neutral writing | porque, como |
| Essay / journalism | como, uma vez que, visto que |
| Academic / legal | dado que, uma vez que, atendendo a que |
| Literary | posto que, pois (often old-fashioned) |
Common Mistakes
❌ Não vim por que estava cansado.
Incorrect — for the conjunction because, write porque as one word.
✅ Não vim porque estava cansado.
I didn't come because I was tired.
❌ Ninguém sabe o porque da sua decisão.
Incorrect — the noun the reason is porquê, with accent.
✅ Ninguém sabe o porquê da sua decisão.
Nobody knows the reason for his decision.
❌ Porquê que estás triste?
Incorrect — the é que emphasis construction requires porque (not porquê) at the start.
✅ Porque é que estás triste?
Why are you sad? (EP colloquial, completely standard)
✅ Por que razão estás triste?
For what reason are you sad? (formal)
❌ Já que estejas aqui, ajuda-me.
Incorrect — causal clauses always take the indicative, not the subjunctive.
✅ Já que estás aqui, ajuda-me.
Since you're here, help me.
❌ Fiquei em casa porque haja muito trânsito.
Incorrect — causal conjunctions require the indicative.
✅ Fiquei em casa porque havia muito trânsito.
I stayed home because there was a lot of traffic.
❌ Estou cansado, Porque trabalhei todo o dia.
Incorrect capitalization — porque is lowercase mid-sentence.
✅ Estou cansado porque trabalhei todo o dia.
I'm tired because I worked all day.
❌ Como não vou à festa porque estou doente.
Incorrect — you cannot have como and porque introducing the same clause.
✅ Como estou doente, não vou à festa.
Since I'm sick, I'm not going to the party.
✅ Não vou à festa porque estou doente.
I'm not going to the party because I'm sick.
Key Takeaways
- All causal conjunctions take the indicative. Never the subjunctive.
- Porque is the universal because; como opens a sentence with the cause; já que is colloquial since; visto que / uma vez que / dado que are formal.
- The four-way distinction porque / por que / porquê / por quê is primarily orthographic: porque = conjunction, por que = preposition + relative, porquê = noun or end-stressed question word.
- Como as a causal always sits at the beginning of the sentence and presents background information.
- Distinguish cause (porque
- ind) from purpose (para que
- subj) — same English "why", different Portuguese constructions.
- ind) from purpose (para que
- Posto que and pois carry archaic/colloquial flavour; pick them deliberately for stylistic effect.
Related Topics
- Purpose Clauses (Para Que, A Fim De Que)B1 — Saying 'in order to / so that' in Portuguese — the split between finite (subjunctive) and non-finite (infinitive) purpose clauses.
- Result Clauses (Tão...Que, Tanto...Que, De Modo Que)B1 — How Portuguese expresses consequence — so tired that I fell asleep, so much rain that the river flooded — and how result clauses differ from purpose clauses.
- Concessive Clauses (Embora, Apesar De, Mesmo Que)B1 — Saying although/even though/despite in Portuguese — the family of conjunctions that pair with the subjunctive, the infinitive, or (rarely) the indicative.
- Temporal Clauses (Quando, Enquanto, Assim Que, Até Que)B1 — Time-expressing subordinate clauses in Portuguese — which conjunction takes which mood, with a full map of quando, enquanto, depois que, antes que, assim que, logo que, até que, and mal.
- Advanced Discourse ConnectorsC1 — The formal connectors that structure educated Portuguese writing — contrast, consequence, addition, exemplification, conclusion — with register notes and placement rules.