Causal Conjunctions (Porque, Pois, Já que, Visto que) | Portuguese (Portugal) Grammar

Causal conjunctions (conjunções causais) introduce the reason for something. English uses "because," "since," "as," and "given that"; Portuguese has an even richer toolkit, sorted by register and by whether the cause is new information or already shared with the listener. This page walks through the whole family, pays close attention to the indicative–subjunctive contrast after porque, and clarifies how the prepositional expressions devido a and em virtude de plug into the same system.

The one decision that will most improve your Portuguese in this area is learning when not to use porque. If the reason is already known to the listener ("since you are already here, help me"), PT-PT strongly prefers já que, como, or uma vez que. Using porque there is not wrong, but it misses a nuance that native speakers would catch.

Porque — the neutral "because"

Porque is the default causal conjunction. It introduces new information — the reason the listener did not previously know. It normally follows the main clause and always takes the indicative.

Não fui à festa porque estava doente.

I didn't go to the party because I was sick.

Compraram uma casa nova porque vão ter outro filho.

They bought a new house because they're going to have another child.

Vou ficar em casa porque está a nevar.

I'm going to stay home because it's snowing.

Negated cause: não porque + subjunctive

There is one situation where porque does trigger the subjunctive: when the cause is negated. The logic is that a negated cause is not being asserted as fact — you are rejecting a false reason and implying the real one.

Não fiz isso porque tivesse medo, mas porque achei justo.

I didn't do it because I was afraid, but because I thought it was right. (subjunctive *tivesse* — the fear is denied as motive)

Gosto dela não porque seja bonita, mas porque é inteligente.

I like her not because she's pretty, but because she's smart. (subjunctive *seja* — prettiness is denied as motive)

Compare with an unnegated porque, which stays in the indicative:

Gosto dela porque é inteligente.

I like her because she is smart. (indicative *é*)

💡

This subjunctive after não porque is one of those small but revealing features of Portuguese. The intuition: if you negate the cause, you are treating it as a counterfactual possibility ("not in the world where that is the reason"), and Portuguese marks counterfactuality with the subjunctive. This logic recurs across the language.

Pois — the formal / post-posed causal

Pois is a tricky word. As a causal conjunction it means "for" or "because," and it typically follows the main clause, often with a comma before it. It belongs to written and semi-formal registers.

Vou sair, pois está um belo dia de sol.

I'm going out, for it's a beautiful sunny day.

Fiquei em casa, pois não me sentia bem.

I stayed home, as I wasn't feeling well.

Beware: pois has several other lives in PT-PT. As a conclusive conjunction (roughly "so"), it usually sits mid-clause between commas: Vamos, pois, começar. ("Let's begin, then.") As a spoken filler or agreement marker, it means something like "right" or "yeah" — and PT-PT speakers use it constantly: — Faz frio, não faz? — Pois. See the discourse cause-effect page for more on this.

Como — "since," clause-initial

Como as a causal conjunction means "since" or "as" in the sense of "given that." It has one firm rule: it must come at the start of the sentence, introducing the cause before the main clause. It takes the indicative.

Como chovia muito, ficámos em casa.

Since it was raining a lot, we stayed home.

Como não tenho tempo hoje, deixamos para amanhã.

As I don't have time today, we'll leave it for tomorrow.

Como já conheces a cidade, podes guiar-nos.

Since you already know the city, you can guide us.

💡

Como and porque are not interchangeable. Como introduces the cause at the start of the sentence and treats it as shared background; porque follows the main clause and introduces the cause as new information. Como não tenho tempo, fico vs Fico porque não tenho tempo — the first frames the cause as given; the second asserts it.

Já que — "since, given that"

Já que introduces a reason that the speaker assumes is already known to the listener. It can go before or after the main clause. It is neutral in register — common in both speech and writing — and always takes the indicative.

Já que estás aqui, ajuda-me a fazer o jantar.

Since you're here, help me make dinner.

Não vale a pena insistir, já que ele nunca muda de opinião.

It's not worth insisting, since he never changes his mind.

Já que não percebes, eu explico outra vez.

Since you don't get it, I'll explain again.

Já que and como overlap considerably; the main difference is placement. Como must be clause-initial; já que is flexible.

Uma vez que — "given that"

Uma vez que is the slightly more formal sibling of já que. It belongs in essays, reports, and formal emails, and carries a flavour of "given the fact that." Indicative only.

Uma vez que o prazo é curto, temos de começar já.

Given that the deadline is short, we have to start now.

Não posso autorizar a despesa, uma vez que ultrapassa o orçamento.

I can't authorise the expense, given that it exceeds the budget.

Visto que — "seeing that"

Visto que (literally "seen that") has the same semantic weight as uma vez que but is slightly more bookish. It is the go-to choice in formal written Portuguese, especially in legal and administrative style.

Visto que os resultados são inconclusivos, serão realizados novos testes.

Seeing that the results are inconclusive, further tests will be carried out.

Visto que ninguém se opôs, a proposta foi aprovada.

Since no one objected, the proposal was approved.

Dado que — "given that"

Dado que is the most academic of the family. You see it in theses, legal briefs, editorials, and formal correspondence. In conversation it sounds bookish.

Dado que a investigação ainda está em curso, não podemos divulgar informações.

Given that the investigation is still underway, we cannot disclose information.

Dado que se trata de um caso sensível, preferimos não comentar.

Given that this is a sensitive case, we prefer not to comment.

Register table

Conjunction	Register	Typical position	Shared/new info	Mood
porque	neutral (any register)	after main clause	new	indicative (subjunctive if negated)
pois (causal)	formal / written	after main clause	new or contextual	indicative
como	neutral	clause-initial only	shared	indicative
já que	neutral	flexible	shared	indicative
uma vez que	semi-formal	flexible	shared	indicative
visto que	formal	flexible	shared	indicative
dado que	formal / academic	flexible	shared	indicative

Noun-phrase causes: devido a, por causa de, em virtude de

When the cause is not a full clause but a noun phrase, Portuguese uses a different set of expressions — technically prepositional locutions (locuções prepositivas) rather than conjunctions. They perform the same communicative job, though.

Expression	Meaning	Register
por causa de + NP	because of	neutral / colloquial
devido a + NP	due to	neutral / formal
graças a + NP	thanks to (positive)	neutral
por culpa de + NP	because of (blame)	neutral
em virtude de + NP	by virtue of	formal
em razão de + NP	by reason of	formal
face a + NP	faced with	semi-formal / journalistic
à conta de + NP	on account of	colloquial

O voo foi cancelado devido ao mau tempo.

The flight was cancelled due to the bad weather.

Chegámos atrasados por causa do trânsito.

We arrived late because of the traffic.

Graças à tua ajuda, acabei o trabalho a tempo.

Thanks to your help, I finished the work on time.

Em virtude das recentes alterações legais, o contrato terá de ser revisto.

By virtue of the recent legal changes, the contract will have to be revised. (formal)

💡

Graças a is reserved for positive causes and por culpa de for negative ones. Saying graças à chuva o jogo foi cancelado is a common but jarring mistake — it implies the rain was a good thing. The neutral devido a or por causa de is the safe choice when the cause could be read either way.

English "because" vs "since"

English speakers often need to choose between "because" and "since" and hope Portuguese makes the same cut. It does not — quite.

"Because" + new information → porque
"Since" meaning "given that" (shared info) → já que, uma vez que, como
"Since" meaning "from the time that" → desde que (temporal — see the temporal page)

Não posso ir porque tenho de trabalhar.

I can't go because I have to work. (new reason)

Já que tens de trabalhar, desistes de ir connosco?

Since you have to work, are you giving up on coming with us? (shared reason)

Não o vejo desde que saiu do Porto.

I haven't seen him since he left Porto. (temporal)

The third sentence is the one English speakers misread most often: desde que in that sense is temporal, not causal.

Punctuation

Porque usually has no comma before it, because the cause is integrated into the main assertion: Fiquei em casa porque estava doente. A comma creates a slight pause and is possible but stylistic.
Como clauses fronted at the start are always followed by a comma: Como chovia, ficámos em casa.
Já que, uma vez que, visto que, dado que when fronted take a comma; when they follow, usually no comma — though it is common to add one for clarity: Não vou, uma vez que estou cansado.
Pois as a causal takes a comma before it: Vou sair, pois está sol.

Causal clauses in context

In a spoken exchange

— Porque não vieste ontem? — Porque me aconteceu uma coisa inesperada.

— Why didn't you come yesterday? — Because something unexpected happened to me.

In a news article

O comboio chegou com duas horas de atraso, uma vez que uma árvore caiu sobre a linha.

The train arrived two hours late, as a tree had fallen on the tracks.

In a formal letter

Lamentamos informar que, dado que os documentos estão incompletos, o seu pedido não pode ser processado.

We regret to inform you that, given that the documents are incomplete, your request cannot be processed.

In a conversation with a friend

Já que estás a ir ao supermercado, podes trazer-me leite?

Since you're going to the supermarket anyway, can you bring me some milk?

Common mistakes

❌ Porque não tenho tempo, não posso ir.

Clumsy — *porque* does not normally sit at the start of a sentence in declarative use; use *como* there.

✅ Como não tenho tempo, não posso ir. / Não posso ir porque não tenho tempo.

Since I don't have time, I can't go.

❌ Já que tenho uma coisa importante para te dizer.

Incomplete — *já que* needs both a reason clause and a consequence.

✅ Já que estás aqui, tenho uma coisa importante para te dizer.

Since you're here, I have something important to tell you.

❌ Graças à chuva, o jogo foi cancelado.

Stylistic mismatch — *graças a* is positive; the rain is an unwanted cause.

✅ Devido à chuva, o jogo foi cancelado. / Por causa da chuva, o jogo foi cancelado.

Because of the rain, the game was cancelled.

❌ Não o vejo porque saiu de casa.

If the meaning is 'since he left home' (temporal), this is wrong.

✅ Não o vejo desde que saiu de casa.

I haven't seen him since he left home.

❌ Não fiz isso porque tinha medo.

If you mean to **deny** fear as the motive, you need the subjunctive.

✅ Não fiz isso porque tivesse medo (, mas porque achei justo).

I didn't do it because I was afraid (but because I thought it was right).

Key takeaways

Porque is neutral; pois is formal/post-posed; já que, uma vez que, visto que, dado que and como all frame the cause as shared background.
Porque takes the indicative normally; the subjunctive only when the cause is explicitly negated (não porque tivesse medo).
Como must be clause-initial; the others are flexible.
For noun-phrase causes, use devido a, por causa de, graças a (positive), por culpa de (blame), or the formal em virtude de / em razão de.
English "since" is ambiguous — it can be causal (já que) or temporal (desde que). Keep them separate.
Register matters: dado que in a text message sounds pedantic; porque in a legal opinion looks lazy.