Causal conjunctions explain why something happened or is true. Spanish has several, and while they can often be translated by because, they are not quite interchangeable. The differences come down to word order, formality, and whether the cause is new information or something already known.
Porque: the everyday "because"
Porque is by far the most common causal conjunction. It introduces the direct reason for what was just said, and — crucially — it answers the question ¿por qué? (why?). It almost always appears in the middle of a sentence, never at the start.
Estudio español porque quiero viajar a México.
I study Spanish because I want to travel to Mexico.
Porque is followed by the indicative when the cause is real, and by the subjunctive only in negative structures like no porque... (meaning not because).
No lo hago porque quiera, sino porque debo.
I don't do it because I want to, but because I have to.
Como: "since" at the start of a sentence
Como introduces a cause that is already known to the listener or that sets the stage for the main clause. It must come at the beginning of the sentence, never after the main verb. In English, it usually corresponds to since or as.
Como llovía, me quedé en casa.
Since it was raining, I stayed home.
Como no tenía dinero, no compré nada.
Since I didn't have any money, I didn't buy anything.
If you flipped the clauses, you could not use como; you would switch to porque: Me quedé en casa porque llovía.
Ya que and puesto que: given that
Ya que and puesto que both mean since or given that. They present a cause as obvious, uncontroversial, or already agreed upon. Unlike como, they can appear at the start or in the middle of a sentence. Puesto que is slightly more formal.
Ya que estás aquí, ayúdame con esto.
Since you're here, help me with this.
Puesto que no hay más preguntas, terminamos la reunión.
Given that there are no more questions, we'll end the meeting.
Both take the indicative, since the cause is presented as factual.
Pues: a colloquial "because" (and a filler)
Pues has two lives. As a causal conjunction, it is a slightly old-fashioned or literary way to say because or for:
No saldremos, pues está lloviendo.
We won't go out, for it's raining.
Much more commonly in spoken Latin American Spanish, pues is a discourse marker — a filler like well or so: Pues, no sé... (Well, I don't know...). You'll hear it constantly in everyday conversation, especially in Mexico, Colombia, and Central America.
Pues, la verdad no estoy seguro.
Well, to be honest I'm not sure.
In this filler role, pues has no real causal meaning — it just buys the speaker a moment to think, similar to the English well....
—¿Vienes con nosotros? —Pues... depende.
—Are you coming with us? —Well... it depends.
Quick comparison
| Conjunction | Meaning | Position | Register |
|---|---|---|---|
| porque | because | middle only | neutral |
| como | since (new context) | beginning only | neutral |
| ya que | since, given that | beginning or middle | neutral |
| puesto que | given that | beginning or middle | formal |
| pues | for, because | middle | literary |
All the conjunctions on this page (except the negative-only no porque) take the indicative, because they describe real causes.
Common mistakes
❌ Como no tengo dinero. Porque no voy.
Wrong: mixing como and porque in separate sentences — pick one.
✅ No voy porque no tengo dinero.
Correct: porque introduces the reason after the main clause.
❌ Porqué estás triste, no quieres salir.
Wrong: porqué (noun = 'the reason') is not the conjunction.
✅ Porque estás triste, no quieres salir.
Correct: porque (one word, no accent) is the conjunction.
❌ Porque llovía, no salimos.
Wrong word order: como introduces the reason when it comes first.
✅ Como llovía, no salimos.
Correct: como + reason at the start of the sentence.
For consequence conjunctions (the flip side of cause), see Result: Así que, Por eso, De modo que. For purpose clauses like so that, see Purpose: Para que, A fin de que.
Related Topics
- Temporal: Cuando, Mientras, Hasta queB1 — How to build time clauses in Spanish and choose between indicative and subjunctive after cuando, mientras, hasta que, and friends.
- Result: Así que, Por eso, De modo queB1 — How to express consequence and result in Spanish with así que, por eso, por lo tanto, and de modo/manera que.
- Purpose: Para que, A fin de queB2 — How to express so that and in order that with para que, a fin de que, and related purpose conjunctions, all with the subjunctive.