The preposition por is one of the hardest-working words in Portuguese. It covers ideas that English splits across half a dozen prepositions: by, through, for, because of, per, via. If you have studied Spanish, you will recognise much of the territory, but European Portuguese adds its own wrinkles — most notably a set of obligatory contractions (pelo, pela, pelos, pelas) and a slightly different idiomatic feel. This page maps all the main uses of por and shows you how to choose it over para, which is the other half of the pair.
The big picture
Everything por does can be traced back to a single image: passage. Something moves through, by, across, or because of something else. Whether it is a cause acting on a result, a messenger travelling on a route, or an agent performing an action in a passive sentence, por always marks the path between two things rather than the endpoint.
This is the core contrast with para. Para points to a destination, a goal, a recipient. Por points to the channel, the cause, the route, the reason things happen. Keep this mental picture handy as we go through the individual uses — it will help you predict the right preposition in sentences you have never seen before.
Obligatory contractions: pelo, pela, pelos, pelas
Before we look at meaning, a housekeeping rule: por always contracts with the definite article. You cannot write por o or por a in modern Portuguese — these forms have been frozen into single words for centuries.
| Combination | Contraction |
|---|---|
| por + o | pelo |
| por + a | pela |
| por + os | pelos |
| por + as | pelas |
These contractions are used in every register, from casual texting to legal documents. There is no situation in which the uncontracted form is acceptable.
O livro foi publicado pela Gradiva.
The book was published by Gradiva.
Passámos pelo parque ao fim da tarde.
We went through the park in the late afternoon.
por o or por a, stop and contract. These are among the most frequent orthographic errors learners make, and they are always wrong. There is no exception.With indefinite articles and with personal pronouns, however, por does not contract: por um motivo, por uma razão, por mim, por ti, por ele, por si.
1. Agent in the passive voice — "by"
When something is done by someone, Portuguese marks the agent with por (or its contracted form). This matches English "by" almost exactly.
O Lusíadas foi escrito por Luís de Camões.
The Lusiads was written by Luís de Camões.
A casa foi desenhada pelo arquiteto Siza Vieira.
The house was designed by the architect Siza Vieira.
A encomenda vai ser entregue pelos correios amanhã.
The package will be delivered by the post office tomorrow.
Note how the article triggers contraction: pelo arquiteto, pelos correios. Leaving these uncontracted is a beginner mistake that immediately marks your writing as foreign.
2. Cause and reason — "because of"
This is where por gets interesting. When an event has a cause — a reason, a trigger, a fault — Portuguese typically uses por. English here often says "because of," "out of," "due to," or sometimes just "for."
Cheguei atrasado por causa do trânsito.
I arrived late because of the traffic.
Ela não foi ao trabalho por estar doente.
She didn't go to work because she was sick.
Fiz isto por ti.
I did this for you (for your sake, because of you).
The last example is the classic pitfall. In English, "I did this for you" can mean either "aimed at you" (purpose → para) or "because of you, for your sake" (cause → por). If the sentence really means out of love for you or on your behalf, Portuguese wants por. If it means as a gift destined for you, the answer is para.
Fixed cause expressions
Portuguese has a cluster of stock phrases that all build on the cause sense of por. Learn these as units:
| Expression | Meaning |
|---|---|
| por causa de | because of |
| por isso | that's why, therefore |
| por esse motivo | for that reason |
| por culpa de | through someone's fault |
| por falta de | for lack of |
Está a chover; por isso levei o guarda-chuva.
It's raining; that's why I took my umbrella.
3. Means and manner — "by (means of)"
When you specify the channel used to accomplish something — phone, email, post, air — Portuguese uses por. English usually says "by" here too, though sometimes "through" or "via."
Avisa-me por mensagem quando chegares.
Text me when you get there.
Preferimos receber a confirmação por email.
We prefer to receive the confirmation by email.
A carta chegou por correio registado.
The letter arrived by registered post.
Mandei os documentos por fax, ainda há quem peça.
I sent the documents by fax — there are still people who ask for it.
Notice that por does not take an article in these set phrases: por telefone, por email, por correio, por fax, por avião. Adding an article changes the meaning slightly: pelo telefone = "through the (specific) phone," usually pointing to a particular device.
4. Exchange and substitution — "for" (in trades)
When one thing is swapped for another, or when you pay a price, por marks what is given up or received in return. This is the "in exchange for" sense.
Troquei os euros por dólares antes da viagem.
I exchanged the euros for dollars before the trip.
Paguei cinquenta euros por este par de sapatos.
I paid fifty euros for this pair of shoes.
Não trocaria isto por nada no mundo.
I wouldn't trade this for anything in the world.
The same logic extends to symbolic exchange — dying for a cause, sacrificing for a person:
Muitos deram a vida pela pátria.
Many gave their lives for the homeland.
5. Route and path — "through, along, via"
Here por really shows its core meaning of passage. Any time you describe the route a movement takes — not where it ends, but what it crosses — you reach for por.
Passei pela Baixa a caminho de casa.
I went through the Baixa on my way home.
No verão adoro viajar pela Europa de comboio.
In summer I love travelling around Europe by train.
Vieste pela autoestrada ou pela nacional?
Did you come on the motorway or the national road?
This use is a favourite trap for English speakers. We often say "I went to the park" when we really mean we passed through it; in Portuguese, if the park is the route, you need passar pelo parque, not ir ao parque.
6. Duration — "for" (a period of time)
Por can mark the length of time an action lasts. In European Portuguese this use is a little less common in casual speech than in Brazilian — natives often prefer durante or simply no preposition at all — but it is still standard and frequent.
Vou ficar em Lisboa por uns dias antes de voltar.
I'm going to stay in Lisbon for a few days before going back.
Estivemos sem eletricidade por mais de duas horas.
We were without power for more than two hours.
Ele viveu em Paris por dois anos enquanto estudava.
He lived in Paris for two years while he was studying.
por is a touch more deliberate.7. Distribution and rate — "per"
When you distribute something across a unit — per person, per hour, per week — por is the word. This matches English "per" and "a" (as in "three times a week").
O curso custa cinquenta euros por pessoa.
The course costs fifty euros per person.
Ele ganha vinte euros por hora a dar explicações.
He earns twenty euros an hour tutoring.
Fazemos ginásio três vezes por semana.
We go to the gym three times a week.
8. Approximate location — "around, somewhere in"
When the location is vague — somewhere around here, over there — Portuguese uses por followed by a place adverb. English tends to use "around" or "somewhere."
Deixei o telemóvel por aqui, mas não o encontro.
I left my phone around here somewhere, but I can't find it.
Por onde andas? Não te vejo há séculos.
Where have you been? I haven't seen you in ages.
Por lá o tempo está melhor do que em Lisboa.
Over there the weather is better than in Lisbon.
9. On behalf of — "on someone's behalf, in place of"
Por can mean acting in place of someone, representing them, or covering for them.
Ela falou pelos colegas todos na reunião.
She spoke on behalf of all her colleagues in the meeting.
10. Idiomatic expressions
A huge amount of everyday Portuguese lives inside fixed phrases built on por. Most of them are opaque — you cannot predict the meaning from the parts — so treat each as a lexical item to memorise.
| Expression | Meaning |
|---|---|
| por favor | please |
| por acaso | by chance, incidentally |
| por exemplo | for example |
| por fim | finally, at last |
| por enquanto | for now |
| por agora / por ora | for the time being |
| por sinal | as it happens, by the way |
| por completo | completely |
| por certo | surely, for sure |
| por pouco | almost (with a negative outcome narrowly avoided) |
Empresta-me a caneta, por favor.
Lend me the pen, please.
Por acaso, encontrei a Joana no supermercado.
As it happens, I ran into Joana at the supermarket.
Por enquanto fica assim, depois vemos.
Leave it like that for now, we'll see later.
Por pouco não perdia o comboio.
I almost missed the train.
Por vs. para — the essential contrast
This is the great divide of Portuguese prepositions. Getting it right is worth more than any single rule you will learn in this course. The working test:
- If you can rephrase the sentence as because of X, through X, in exchange for X, use
por. - If you can rephrase it as destined for X, in order to X, aimed at X, use
para.
Fiz o bolo pela minha mãe.
I made the cake because of my mother (because she asked me to, for her sake).
Fiz o bolo para a minha mãe.
I made the cake for my mother (to give it to her).
These are two different sentences in Portuguese even though English collapses them both into "for my mother." The first tells us why the cake was made; the second tells us who gets it. See Por vs Para for a complete side-by-side.
Common Mistakes
Learners coming from English — and even from Spanish — trip on a predictable set of issues with por. Here are the ones that show up again and again.
❌ Passei por o parque.
Incorrect — por must contract with the article.
✅ Passei pelo parque.
I went through the park.
❌ Obrigado para a ajuda.
Incorrect — 'thanks for' expresses cause, not destination.
✅ Obrigado pela ajuda.
Thanks for the help.
❌ Vou ficar aqui para dois dias.
Incorrect — this is a duration, not a destination.
✅ Vou ficar aqui por dois dias.
I'm going to stay here for two days.
❌ Troquei o carro para uma bicicleta.
Incorrect — 'exchange for' is por, not para.
✅ Troquei o carro por uma bicicleta.
I traded the car for a bicycle.
❌ Ele fez-me um favor, por isso eu fiz um bolo para ele.
Careful — this one is actually correct! The bolo's destination is ele (para), but the isso refers to the cause of your action.
The last pair illustrates that por and para can appear in the same sentence doing different work — one marks cause, the other marks destination. That is exactly the split you are learning to feel.
Key Takeaways
Pormarks passage: the agent, cause, means, route, or rate through which something happens.- It always contracts with definite articles:
pelo, pela, pelos, pelas. - Contrast with
para, which points to destinations and purposes. - A huge number of high-frequency expressions are built on
por— treat them as fixed vocabulary. - When you are unsure between
porandpara, ask: "Is this a cause/route, or a destination/goal?" The answer picks your preposition.
Related Topics
- The Preposition paraA1 — Uses of the preposition para — purpose, destination, recipient, deadline, comparison, and the para vs. por distinction.
- por vs. para: The Classic PairA2 — The definitive PT-PT comparison of por and para — cause vs. purpose, agent vs. recipient, route vs. destination, duration vs. deadline, and the subtle cases that trip up every learner.
- Contractions with porA2 — How por contracts obligatorily with definite articles to produce pelo, pela, pelos, and pelas — with historical notes and what does not contract.
- Portuguese Prepositions OverviewA1 — Introduction to Portuguese prepositions and their uses, including the obligatory contractions that set European Portuguese apart.
- Prepositions of Time: em, a, de, para, por, desde, até, duranteA2 — How Portuguese uses em, a, de, para, por, desde, até, durante, and há to mark points, durations, starting points, endpoints, and frequencies in time.