Por is one of the busiest prepositions in Portuguese. English splits its jobs across half a dozen words — for, by, through, because of, per, along — so the single hardest thing for English speakers is realizing that all of these can collapse into one Portuguese word. The unifying idea is that por looks backward or sideways: at the cause that produced something, the path it travelled through, the thing it was exchanged for, or the agent that did it. (Its partner para, covered on its own page, points forward — toward goals and destinations.)
This page covers every core use of por, plus the one mechanical rule you cannot skip: in Brazilian Portuguese, por always fuses with a following definite article into pelo / pela / pelos / pelas.
The mandatory contractions
Before meaning, learn the mechanics. Unlike de and em, which contract with articles only as a convenience, por + article is obligatory. You will never see "por o" or "por a" in correct Brazilian Portuguese.
| por + | contraction | example |
|---|---|---|
| o | pelo | pelo correio (by mail) |
| a | pela | pela manhã (in the morning) |
| os | pelos | pelos campos (through the fields) |
| as | pelas | pelas ruas (through the streets) |
Mandei o contrato pelo correio ontem.
I sent the contract by mail yesterday.
Gosto de correr pela manhã, antes do trabalho.
I like to run in the morning, before work.
Note that por does not contract with a bare noun or an indefinite article: por amor (out of love), por uma boa razão (for a good reason) stay separate.
Cause and reason — "because of," "out of"
The most common job of por is to explain why. It introduces the cause or motive behind an action. English usually reaches for because of, out of, or for.
Ela fez tudo isso por amor aos filhos.
She did all of that out of love for her kids.
Não fui à festa por causa da chuva.
I didn't go to the party because of the rain.
Por isso é que eu não confio nele.
That's exactly why I don't trust him.
That last one, por isso ("for that reason / that's why"), is one of the most frequent connectors in spoken Brazilian Portuguese. Learn it as a chunk.
Means and manner — "by," "via"
When you say how something travels or gets done — by phone, by email, via a channel — that channel takes por. This is the English by of by phone, by car.
A gente combinou tudo por telefone.
We arranged everything by phone.
Me manda os detalhes por e-mail, por favor.
Send me the details by email, please.
Soube da notícia pela televisão.
I found out about the news on TV (via TV).
Through and along — movement across space
Por describes motion through, along, or around a space — the path of the movement, not its endpoint (the endpoint would be para or a). This is where the contractions show up constantly.
Passei pela sua rua e vi que a luz estava acesa.
I went past your street and saw the light was on.
Eles viajaram pelo Brasil inteiro de moto.
They travelled all across Brazil by motorcycle.
Andamos pelo centro a tarde toda.
We walked around downtown the whole afternoon.
Duration — "for" a span of time
A length of time over which something lasts takes por (though in casual speech Brazilians often drop it: Morei lá dois anos). Contrast this with para, which marks a deadline, not a span.
Ela morou no Japão por dois anos.
She lived in Japan for two years.
Vou ficar em São Paulo por uma semana.
I'm going to stay in São Paulo for a week.
Exchange and rate — "for," "per"
When something is traded, paid, or measured against another thing, that's por: the price for an item, the speed per hour, the substitution of one thing for another.
Paguei cinquenta reais por isso e me arrependi.
I paid fifty reais for this and regretted it.
O carro fazia cento e vinte por hora na estrada.
The car was doing a hundred and twenty per hour on the highway.
Troquei meu celular antigo por um novo.
I traded my old phone for a new one.
The agent in passive sentences — "by"
In a true passive sentence (ser + past participle), the doer of the action is introduced by por. This is the English by of written by, built by. Because the agent is usually a definite noun, you'll often get the contraction.
Esse prédio foi projetado por um arquiteto famoso.
This building was designed by a famous architect.
O bolo foi feito por mim, viu? Não comprei.
The cake was made by me, you know? I didn't buy it.
As decisões são tomadas pelo conselho.
The decisions are made by the board.
For the full mechanics of passive voice, see the passive sentences page.
Why por and para split — the English trap
English speakers struggle here because English has one word, for, doing the work of two Portuguese prepositions that mean genuinely different things. The mental fix is to ask: is this pointing forward to a goal, or backward to a cause?
- Comprei flores *para minha mãe = I bought flowers *to give to my mom (goal/recipient → para).
- Comprei flores *por minha mãe = I bought flowers *because of my mom — maybe she asked, maybe in her honor (cause → por).
This forward/backward split mirrors Spanish por vs para almost exactly, so if you've studied Spanish, your instincts will transfer. If your only reference point is English for, you'll need to retrain. The full decision tree lives on the por vs para page.
Common Mistakes
❌ Mandei o documento por o e-mail.
Incorrect — 'por + o' must contract.
✅ Mandei o documento pelo e-mail.
I sent the document by email.
❌ Estudo português para viajar por dois anos.
Incorrect — duration is 'por', and here the meaning is muddled.
✅ Estudo português por dois anos.
I've been studying Portuguese for two years (duration → por).
❌ Este presente é por você.
Incorrect — a recipient/gift points forward → para.
✅ Este presente é para você.
This gift is for you.
❌ O livro foi escrito para um jornalista.
Incorrect — the agent of a passive takes 'por', not 'para'.
✅ O livro foi escrito por um jornalista.
The book was written by a journalist.
❌ Passamos para o parque no caminho.
Incorrect — 'through/along a path' is 'por' → pelo.
✅ Passamos pelo parque no caminho.
We went through the park on the way.
Key Takeaways
- Por always looks backward or sideways: cause, means, path, duration, exchange, and the passive agent.
- por + o/a/os/as → pelo/pela/pelos/pelas is mandatory, never optional.
- The forward-looking sense ("for someone," "in order to," "by a deadline") belongs to para, not por.
- Frozen connectors like por isso and por causa de are worth memorizing as whole units.
Now practice Portuguese
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Start learning Portuguese→Related Topics
- Preposition 'Para': For, To, TowardA1 — How 'para' marks purpose, destination, recipient, deadline, and opinion in Brazilian Portuguese — its near-universal spoken reduction to pra/pro and a preview of para vs por.
- Por vs Para: Decision GuideA2 — The forward-pointing para (goal, destination, recipient, deadline) versus the backward-pointing por (cause, path, means, exchange) — with decision tests and minimal pairs.
- Contractions with 'Por' (Pelo, Pela)A2 — Why por always fuses with the definite article into pelo, pela, pelos, and pelas — and why it never contracts with pronouns or demonstratives.
- Passive SentencesB1 — Building passive sentences in Brazilian Portuguese — the ser-passive with 'por', the se-passive for agentless statements, and why everyday speech prefers active recasts.
- Prepositions: OverviewA1 — A map of the Brazilian Portuguese preposition system, the obligatory contractions with articles and pronouns, and why prepositions almost never map one-to-one to English.