English has one main word for cause: because. Spanish has half a dozen, and the choice is not stylistic — it's informational. Porque states a cause the listener doesn't know yet; como assumes the cause as background; ya que and puesto que mark the cause as shared knowledge. Picking the wrong one doesn't make a sentence ungrammatical, but it makes you sound like someone who has memorized vocabulary lists rather than someone who knows how Spanish packages information.
This page covers the everyday causal conjunctions you'll use from A2 onwards: porque, como, ya que, puesto que, dado que, pues, and the non-clausal por + noun/infinitive. The forms are easy. The choice between them is where the work is.
Porque — the default cause
Porque is the everyday word for because. It introduces new information about why something is or happens — information the listener doesn't yet have. It always takes the indicative (cause is presented as fact) and it sits after the main clause, or after a comma if it comes second.
No he ido al trabajo porque estoy malísima, llevo dos días con fiebre.
I haven't gone to work because I'm really ill — I've had a fever for two days.
Llegamos tarde porque había un atasco enorme en la M-30.
We arrived late because there was a huge traffic jam on the M-30.
Me voy ya, porque mañana madrugo.
I'm leaving now because I have to get up early tomorrow.
The structure is statement, porque cause. Speakers default to this order because the main statement usually carries the news ("I haven't gone to work") and the cause explains it ("because I'm ill"). Putting porque first is possible but marked — you would only do it in a question-answer pair: ¿Por qué no has venido? — Porque estoy malísima.
Important orthography: porque (one word, no accent) means because. Distinguish it from:
- ¿Por qué? (two words, accent) — why?, the question word.
- el porqué (one word, accent, with article) — the reason, a noun.
- por que (two words, no accent) — rare, found in fixed prepositional constructions (el motivo por (el) que vino).
Como — backgrounded cause at the start of the sentence
Como meaning because/since has one rigid rule: it must come at the start of the sentence, before the main clause. It also takes the indicative.
Como estoy malísima, no he ido al trabajo.
Since I'm really ill, I haven't gone to work.
Como había un atasco enorme, llegamos tarde.
Since there was a huge traffic jam, we arrived late.
Como no me coges el teléfono, te escribo por aquí.
Since you're not answering the phone, I'm writing to you here.
The difference between porque and como is not the meaning of because — both translate that way. The difference is information packaging. Como signals that the cause is backgrounded, presented as the setup, and the new news is in the main clause. Porque signals the cause itself is the new information.
Compare:
No he ido al trabajo porque estoy malísima.
I haven't gone to work because I'm really ill. — the new info is the cause; the listener already knew I was off work.
Como estoy malísima, no he ido al trabajo.
Since I'm really ill, I haven't gone to work. — the illness is the setup; the new info is that I missed work.
Both sentences describe the same situation, but they answer different implicit questions. Porque answers why didn't you go to work?; como answers what did your illness lead you to do? This is why como always comes first — backgrounded information has to be presented before the main news, exactly like setting up a stage.
Ya que and puesto que — cause as shared knowledge
Ya que and puesto que introduce a cause that the speaker treats as already known to the listener (or easily acceptable). The closest English match is since in its causal sense, or given that. Both take the indicative. Both can sit at the start or after the main clause.
Ya que estás aquí, ayúdame a mover el sofá.
Since you're here, help me move the sofa.
No quedan entradas, puesto que el concierto se agotó en una hora.
There are no tickets left, since the concert sold out in an hour.
Puesto que ya sabes la verdad, no tiene sentido seguir mintiendo.
Since you already know the truth, there's no point in continuing to lie.
The register difference: ya que is neutral to slightly informal; puesto que is distinctly formal, common in writing, journalism, and academic prose. In everyday speech, a Spaniard is far more likely to say ya que than puesto que. Saying puesto que in a casual conversation isn't wrong, but it lands as bookish.
Dado que (= given that) belongs to the same shared-knowledge family but is even more formal — almost exclusively written, especially in legal, academic, and journalistic registers.
Dado que las inversiones extranjeras han caído un 20 %, el gobierno revisará su política fiscal. (formal/academic)
Given that foreign investment has fallen by 20%, the government will review its fiscal policy.
The information-packaging hierarchy
Once you see the four conjunctions side by side, the system is clean:
| Conjunction | Information status of the cause | Position | Register |
|---|---|---|---|
| porque | new information | after main clause | neutral, all registers |
| como | backgrounded, set-up | always sentence-initial | neutral, all registers |
| ya que | shared knowledge | either position | neutral to slightly informal |
| puesto que | shared knowledge | either position | formal, mostly written |
| dado que | shared knowledge / premise | usually sentence-initial | formal/academic |
| pues | literary/archaic cause | after main clause | literary, archaic |
Por + noun and por + infinitive — non-clausal cause
When the cause is not a full clause but a noun or an infinitive, Spanish doesn't use porque. It uses the preposition por, which packages cause without a conjugated verb.
No quiero salir por la lluvia.
I don't want to go out because of the rain.
Me han multado por aparcar en doble fila.
They fined me for double-parking.
No fui a la fiesta por estar cansado.
I didn't go to the party because I was tired. / I didn't go to the party on account of being tired.
This is the single most common mistake English speakers make in this area. English allows because + clause freely, so learners reach for porque and produce ungrammatical porque la lluvia or porque cansado. Spanish blocks that — if there's no conjugated verb, you can't use porque. You have to either:
- Swap in a full clause with a verb: porque llueve, porque estoy cansado.
- Use por + noun/infinitive: por la lluvia, por estar cansado.
No te llamé porque estaba cansado. (full clause)
I didn't call you because I was tired.
No te llamé por estar cansado. (por + infinitive)
I didn't call you because I was tired. / out of tiredness.
Both are correct. The por + infinitive version is slightly more compressed and often sounds more natural in writing or in a deliberate, reflective tone. In speech, porque + clause is more common.
A subtle nuance: por + infinitive can also mean for the sake of doing, especially with verbs of effort. Lo hago por ayudarte (I do it (in order) to help you) blurs the line between cause and purpose. When ambiguity matters, use para for purpose and por for cause — see por vs para.
Pues — literary and archaic
Pues meaning because/for is literary and archaic. You'll see it in 19th-century novels and elevated prose; you should recognise it but not use it.
No habló más, pues la emoción le ahogaba la voz. (literary)
He spoke no more, for emotion choked his voice.
A critical separate point: pues at the start of an utterance is something completely different — it's a discourse filler meaning well..., so..., then..., hugely common in spoken Spanish. Pues no sé, depende de la hora (well, I don't know, it depends on the time). That conversational pues has nothing to do with the archaic causal pues — they just share a spelling.
Causal infinitive with de tanto / a fuerza de
A B1+ pattern worth recognising. De tanto + infinitive (= from so much X-ing) and a fuerza de + infinitive (= by dint of X-ing) express cause through repeated or intense action.
Me duele la espalda de tanto cargar cajas.
My back hurts from carrying so many boxes.
A fuerza de practicar todos los días, ha mejorado muchísimo.
By practising every day, he has improved enormously.
Both are idiomatic causal expressions native speakers use frequently. They don't fit the porque/como/ya que paradigm but live in the same semantic space.
Common Mistakes
❌ No quiero salir porque la lluvia.
Porque requires a full clause with a conjugated verb. With a bare noun, use por.
✅ No quiero salir por la lluvia.
I don't want to go out because of the rain.
❌ Porque estoy malísima, no he ido al trabajo.
Porque at the start of a declarative sentence sounds unnatural — that slot belongs to como. Reserve porque-first for direct answers to ¿Por qué?
✅ Como estoy malísima, no he ido al trabajo.
Since I'm really ill, I haven't gone to work.
❌ No vine por que estaba enfermo.
The conjunction is one word: porque. Por que (two words, no accent) is only used in rare prepositional patterns.
✅ No vine porque estaba enfermo.
I didn't come because I was ill.
❌ Me han multado porque aparcar en doble fila.
Aparcar is an infinitive — porque can't introduce an infinitive. Use por + infinitive.
✅ Me han multado por aparcar en doble fila.
They fined me for double-parking.
❌ ¿Porque no viniste ayer?
The question word why is two words with an accent: ¿por qué?
✅ ¿Por qué no viniste ayer?
Why didn't you come yesterday?
Key takeaways
- Porque is the default everyday because, introduces new information about the cause, sits after the main clause, takes the indicative.
- Como means since (backgrounded cause); always at the start of the sentence; takes the indicative.
- Ya que and puesto que mark the cause as shared knowledge. Puesto que and dado que are more formal — written register.
- Por + noun or por + infinitive is the only way to express cause when there's no conjugated verb: por la lluvia, por estar cansado. Never porque
- bare noun.
- Pues as a causal conjunction is literary/archaic — recognise it, don't use it. The everyday spoken pues (well, so, then) is a different word.
- Watch the spelling family: porque (because) / ¿por qué? (why?) / el porqué (the reason) / por que (rare).
- Causal como answers what did X lead to?; porque answers why did Y happen?. Same cause, different information packaging.
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