Por Isso vs. Por Causa de: Result and Cause in Portuguese
These expressions connect the same two ideas from opposite directions: what happened and why it happened.
Real Life Portuguese · 5 min read · Updated October 14, 2026
The short answer
Por isso means “that is why” or “because of that.” It points back to information already given and introduces the consequence that follows.
Use por isso to state the result
The phrase is useful at the beginning or middle of a sentence. A comma often marks a pause when por isso starts a new clause.
O ônibus atrasou; por isso, chegamos depois das oito.
The bus was late; that’s why we arrived after eight.
Ela trabalha perto de casa e, por isso, vai a pé.
She works near home and, because of that, walks there.
Não conheço a região. Por isso, vou usar o mapa.
I don’t know the area. That’s why I’ll use the map.
Use por causa de to name the cause
Por causa de means “because of” and introduces the reason or circumstance that caused something. Before a masculine singular noun, de + o contracts to do; before a feminine singular noun, de + a becomes da.
The phrase can also appear before plural nouns: por causa dos horários (because of the schedules) and por causa das obras (because of the construction).
O voo atrasou por causa do mau tempo.
The flight was delayed because of the bad weather.
A rua ficou fechada por causa da feira.
The street was closed because of the market.
Mudamos o horário por causa das crianças.
We changed the time because of the children.
Connect one cause and one result
You can express the same relationship with both structures: a cause with por causa de, followed by a result with por isso. This is useful when you want to make the logic easy to follow.
Because por causa de is followed by a noun phrase, use porque before a full clause with its own verb. Compare por causa da chuva and porque estava chovendo.
Choveu muito; por isso, cancelaram o jogo.
It rained a lot; that’s why they canceled the game.
Cancelaram o jogo por causa da chuva.
They canceled the game because of the rain.
Fui de táxi porque estava atrasado.
I took a taxi because I was late.
Put it into practice
Por causa de introduces a reason; por isso introduces what happened as a result. Use porque before a clause with a verb.
Quick practice
Which Portuguese example matches “I took a taxi because I was late”?
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