The preposition por produces one of the tidiest contraction systems in Portuguese: it fuses with the four definite articles (o, a, os, as) to give pelo, pela, pelos, and pelas. These four forms are the only standard modern contractions of por, and they are obligatory in every register, from a quick WhatsApp message to a Supreme Court decision. You will never see por o or por a in correct written Portuguese. This page gives you the full picture — the forms, their history, where they appear, and the predictable errors English speakers make.
The four obligatory contractions
| por + article | Contraction | Literal meaning |
|---|---|---|
| por + o | pelo | by / through / for the (m. sg.) |
| por + a | pela | by / through / for the (f. sg.) |
| por + os | pelos | by / through / for the (m. pl.) |
| por + as | pelas | by / through / for the (f. pl.) |
These contractions behave like single words. They take no hyphen, they carry no special accent, and they slot into the sentence exactly where the separate por + article would otherwise sit.
A encomenda chegou pelo correio esta manhã.
The package arrived by post this morning.
Caminhámos pela praia até ao pôr do sol.
We walked along the beach until sunset.
Passámos pelas ruas estreitas de Alfama ao fim da tarde.
We walked through the narrow streets of Alfama in the late afternoon.
A small note on history
Modern pelo and pela look like simple mergers of por + o, but the story is slightly more interesting. Old Portuguese had two competing forms of the preposition: per and por, both descended from Latin per. Per contracted with articles to give pelo, pela, pelos, pelas — forms already fully frozen by the thirteenth century. Over time, por won out as the standalone form, but it inherited the contractions from its older sibling. That is why the l appears in pelo but not in the uncontracted por: the l is a trace of the per + lo phase of the language, where lo, la, los, las were the Old Portuguese definite articles (still the form in Spanish today).
The upshot for a learner is simple: do not try to decompose pelo back into a visible por + o. Treat it as a single lexical item that happens to carry the grammatical weight of both.
Where the contraction actually lives in a sentence
Because por covers a wide range of meanings — agent, cause, route, exchange, means, duration — the contractions appear across an equally wide range of sentence types. Here are the most frequent contexts in daily use.
Passive agent (by)
Whenever you express who did something in a passive sentence, and that agent carries a definite article, the contraction is forced.
O livro foi escrito pelo autor em apenas três meses.
The book was written by the author in just three months.
A peça foi encenada pela companhia de teatro da universidade.
The play was staged by the university theatre company.
As decisões são tomadas pelos sócios em reunião geral.
Decisions are made by the members at the general meeting.
Route and path (through, along)
The route sense of por — physical passage — constantly collides with articles naming streets, bridges, parks, and other definite places.
Passámos pela ponte 25 de Abril ao sair de Lisboa.
We crossed the 25th of April Bridge as we left Lisbon.
Ele costuma voltar a casa pelos campos, é mais calmo.
He usually walks home through the fields, it's quieter.
Cause and motive (because of, for the sake of)
Pelo amor de Deus, fala mais baixo que os miúdos estão a dormir.
For the love of God, keep your voice down — the kids are asleep.
Agradeço-te pela paciência que tiveste comigo.
Thank you for the patience you had with me.
Temporal reference (during, at a certain time of)
Por combined with time expressions often slides into idioms meaning around, during, or at.
Pela noite, a cidade fica completamente diferente.
At night, the city feels completely different.
Pela manhã cedo, ainda há quem venda peixe na praia.
Early in the morning, there are still people selling fish on the beach.
What does NOT contract with por
Here is where por differs most sharply from de and em. The preposition por forms no other standard contractions. None. Not with indefinite articles, not with demonstratives, not with personal pronouns, not with neuter pronouns. Every combination below is written as two separate words.
With indefinite articles: always separate
Unlike de (which has the optional dum, duma, duns, dumas) and em (which has the optional num, numa, nuns, numas), the preposition por offers no shortcut. You write out por um, por uma, por uns, por umas every time.
Fiz isto por um motivo muito simples.
I did this for one very simple reason.
Trocámos mensagens por uma hora inteira.
We exchanged messages for a whole hour.
Passámos por uns minutos difíceis, mas está tudo bem agora.
We went through a few rough minutes, but everything's fine now.
This is a small orthographic difference with a clear payoff: there is simply nothing to remember. If the article is indefinite, keep the two words apart.
With demonstratives: always separate
De fuses with demonstratives to give deste, dessa, daquele, and so on. Em does the same: neste, nessa, naquele. Por does none of this. The combinations por este, por esse, por aquele, por isto, por isso, por aquilo are always two words.
Passei por este café mil vezes, mas nunca entrei.
I've walked past this café a thousand times, but I've never gone in.
Por aquele caminho, chegamos mais depressa ao centro.
By that road, we get to the centre faster.
Notice in the last example that por isso is one of the most frequent connectors in spoken Portuguese — it means that's why or therefore — and it is always written as two words.
With personal pronouns: always separate
Fiz isto por ti, nunca te esqueças disso.
I did this for you — never forget that.
Ela fez uma viagem de mil quilómetros por ele.
She made a thousand-kilometre trip for him.
Votámos por eles porque merecem uma segunda oportunidade.
We voted for them because they deserve a second chance.
Compare por ele with dele (from de + ele) or nele (from em + ele). Por simply does not participate in that merger.
Idioms built on contracted forms
A substantial chunk of everyday Portuguese lives in fixed expressions with pelo/pela/pelos/pelas. These are worth memorising as units, because their meanings are not strictly predictable from the parts.
| Expression | Meaning |
|---|---|
| pelo menos | at least |
| pelos vistos | apparently, by the looks of it |
| pelo caminho | along the way |
| pelo contrário | on the contrary |
| pelo sim, pelo não | just in case |
| pelo menos isso | at least that much |
| pela primeira vez | for the first time |
| pela última vez | for the last time |
| pelo amor de Deus | for God's sake |
| pela calada | quietly, on the sly (informal) |
Pelos vistos, o voo vai atrasar-se mais uma hora.
Apparently, the flight is going to be delayed another hour.
Leva um guarda-chuva, pelo sim pelo não.
Take an umbrella, just in case.
Pelo menos não está a chover em Lisboa.
At least it's not raining in Lisbon.
Conhecemo-nos pela primeira vez num congresso em Coimbra.
We met for the first time at a conference in Coimbra.
Entraram pela calada, ninguém deu por eles.
They slipped in unnoticed, no one noticed them.
These expressions are so fused that native speakers rarely parse them consciously. Once you know a handful, they begin to act as signposts that alert you to the "passage" logic of por — something is being traversed, justified, or approximated.
Contrast with other prepositions
It is worth lining up por against its neighbours to see how differently they behave.
| Preposition | Contracts with o/a | Contracts with um/uma | Contracts with este/esse/aquele | Contracts with ele/ela |
|---|---|---|---|---|
| de | yes (do, da) | optional (dum, duma) | yes (deste, dessa, daquele) | yes (dele, dela) |
| em | yes (no, na) | optional (num, numa) | yes (neste, nessa, naquele) | yes (nele, nela) |
| a | yes (ao, à) | no | distal only (àquele, àquilo) | no |
| por | yes (pelo, pela) | no | no | no |
| para | no (written); colloquial pra/pró/prà | no | no | no |
Por is the only preposition with exactly one contraction pattern (the definite article) and zero optional variations. That simplicity makes it easy to learn and remember — four forms, all obligatory, used everywhere.
Common mistakes
Transfer errors from Spanish are rare here — Spanish por el stays uncontracted, so Portuguese speakers of Spanish origin quickly learn the obligatory fusion. English speakers tend to overgeneralise: either they forget the contraction entirely, or they invent contractions where none exists.
❌ Passámos por o parque ao fim da tarde.
Incorrect — por must contract with o to produce pelo.
✅ Passámos pelo parque ao fim da tarde.
We walked through the park in the late afternoon.
❌ Fiz isto por a minha família.
Incorrect — por + a must contract to pela.
✅ Fiz isto pela minha família.
I did this for my family.
❌ O livro foi escrito porum autor português.
Incorrect — por does not contract with um. Keep them separate.
✅ O livro foi escrito por um autor português.
The book was written by a Portuguese author.
❌ Peloisso, fiquei em casa.
Incorrect — por isso is never written as one word. Por does not contract with isso.
✅ Por isso, fiquei em casa.
That's why I stayed home.
❌ Pelele, faço qualquer coisa.
Incorrect — por does not contract with ele. Write por ele.
✅ Por ele, faço qualquer coisa.
For him, I'd do anything.
The pattern to internalise: only the four definite articles trigger a contraction. Everything else stays apart.
Key takeaways
- Por contracts obligatorily with the four definite articles: pelo, pela, pelos, pelas.
- These contractions are used in every register and have no uncontracted alternative in writing.
- Por does not contract with indefinite articles, demonstratives, personal pronouns, or neuter pronouns.
- The l in pelo/pela is a historical fossil from the Old Portuguese variant per.
- A cluster of high-frequency idioms uses the contracted form — pelo menos, pelos vistos, pela primeira vez — and these are best learned as fixed expressions.
- When in doubt: contract with o, a, os, as. Leave everything else alone.
Related Topics
- The Preposition porA2 — Uses of the preposition por — agent, cause, means, route, duration, and its obligatory contractions pelo/pela.
- 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.
- All Preposition Contractions (Complete Reference)A2 — The complete reference for all European Portuguese preposition contractions — definite and indefinite articles, demonstratives, and pronouns. Master tables and quick-reference grids.
- Portuguese Prepositions OverviewA1 — Introduction to Portuguese prepositions and their uses, including the obligatory contractions that set European Portuguese apart.