Learn Hardcore Portuguese (Portugal): Em casa, cada um é responsável por arrumar o seu quarto. - At home, each person is responsible for tidying their own room.

Em casa (without an article) is an idiomatic expression meaning:
- at home (your home / the family home, in a general sense)
- It’s like saying “At home, …” as a general rule.
Na casa = em + a casa = “in the house / in the home”, referring to a specific house:
- Na casa dos meus pais = in/at my parents’ house
- Na casa azul da esquina = in the blue house on the corner

So:

Em casa, cada um… = At home, each person… (general rule)
Na casa… would sound like you are specifying a particular house, not stating a general family rule.

What does “cada um” mean exactly, and why is the verb singular (é) and not plural (são)?

Cada um literally means “each one” and is grammatically singular, even though it refers to more than one person in meaning.

cada = each
um = one (masculine form here)

Because it is grammatically singular, the verb must also be singular:

Cada um é responsável… ✅
Cada um são responsáveis… ❌ (ungrammatical)

This is similar to English:

Each one *is responsible… (not *each one are responsible)

Could we say “cada pessoa” instead of “cada um”? Is there any difference?

Yes, you could say “Em casa, cada pessoa é responsável por arrumar o seu quarto.” The meaning is essentially the same.

Subtle differences:

cada um
- Very common and natural in speech.
- Slightly more informal / neutral.
cada pessoa
- Sounds a bit more formal or explicit (“each person”).

Both are correct in European Portuguese; “cada um” is probably the more typical choice in this kind of family-rule sentence.

Why do we say “é responsável por arrumar” and not “é responsável de arrumar” or just “é responsável arrumar”?

With responsável, European Portuguese normally uses the preposition por before a verb in the infinitive:

ser responsável por + infinitive
- É responsável por arrumar o seu quarto. ✅
- He/She is responsible for tidying his/her room.

Using de here would sound odd or incorrect in standard European Portuguese:

é responsável de arrumar ❌

And you cannot drop the preposition:

é responsável arrumar ❌

So, for actions, keep:
ser responsável por + [infinitive]

What exactly does “arrumar” mean here? Is it “to fix”, “to tidy”, or “to clean”?

In European Portuguese, arrumar (um quarto) usually means:

to tidy up / put things in their place / straighten up

It focuses on:

putting clothes away
organizing objects
making the bed
clearing clutter

It does not necessarily mean:

scrubbing, mopping, disinfecting (that’s more limpar = to clean)

Compare:

arrumar o quarto = to tidy the room, put everything in order
limpar o quarto = to clean the room (dust, vacuum, wash, etc.)

In many home contexts, arrumar o quarto is what parents tell children: “Go tidy your room.”

Why is it “por arrumar o seu quarto” and not “para arrumar o seu quarto”? Aren’t both “por” and “para” translated as “for”?

Both por and para can be translated as “for” in English, but they’re used differently.

With ser responsável, the natural choice is por:

ser responsável por + action ✅
- responsible for doing something

Para arrumar would usually express purpose (“in order to tidy”), which doesn’t fit after responsável:

É responsável por arrumar o seu quarto. ✅
- He/She is responsible for tidying his/her room.
É responsável para arrumar o seu quarto. ❌
- Unnatural / incorrect with responsável in this structure.

So you should treat “ser responsável por + infinitive” as a fixed pattern.

Why is it “o seu quarto” and not just “seu quarto”?

In European Portuguese, possessives are very often used with the definite article:

o seu quarto = his/her/your room (literally: the his/her room)
a minha casa = my house
os teus livros = your books (informal singular)

Saying “seu quarto” without the article is technically understandable but sounds unnatural or incomplete in European Portuguese in most contexts, especially in normal speech.

So:

arrumar o seu quarto ✅ (normal EP)
arrumar seu quarto ❌ (sounds wrong in EP; common only in some Brazilian styles/registers)

Does “o seu quarto” mean “his”, “her”, or “your” room? How do we know whose room it is?

Seu/sua/seus/suas are third-person and also sometimes formal second-person possessives, so they’re ambiguous:

o seu quarto can mean:
- his room
- her room
- your room (formal “você” / “o senhor” / “a senhora” in some contexts)

In this sentence:

Cada um é responsável por arrumar o seu quarto.
- Context tells us it means:
  - each person is responsible for tidying *their own room.*

To remove ambiguity in European Portuguese, speakers often say:

o seu próprio quarto = their own room
or replace seu with:
- o quarto dele = his room
- o quarto dela = her room

But in this specific structure with cada um, listeners naturally understand “o seu quarto” as each person’s own room.

Why is “seu” used instead of “teu” or “vosso”?

All three are possessive adjectives, but they match different persons of “you”:

teu / tua / teus / tuas
- informal singular “tu”
- o teu quarto = your room (talking to one person, informally)
seu / sua / seus / suas
- third person (his, her, their)
- and sometimes formal “you” (você, o senhor, a senhora)
vosso / vossa / vossos / vossas
- plural “you all’s” (vós in old/lit. language; or “vocês” in practice)
- o vosso quarto = your (plural) room(s)

In this sentence, “cada um” is a third-person expression (“each one / each person”), so its natural possessive is seu:

Cada um é responsável por arrumar o seu quarto. ✅
- Each one is responsible for tidying his/her own room.

Using teu or vosso would wrongly change it to second person (you), which doesn’t match cada um.

Could we change the word order, for example: “Cada um, em casa, é responsável…” or “Cada um é, em casa, responsável por arrumar…”?

Yes, Portuguese word order is relatively flexible, and those alternatives are possible, but they change the rhythm and sometimes the focus:

Em casa, cada um é responsável por arrumar o seu quarto.
- Most natural, neutral word order.
- Sets the context first (At home), then the rule.
Cada um, em casa, é responsável por arrumar o seu quarto.
- Also correct.
- Slightly more emphasis on cada um (Each one, at home, is responsible…).
Cada um é, em casa, responsável por arrumar o seu quarto.
- Grammatically fine but sounds more formal or written.
- The insertion of “em casa” in the middle feels a bit heavier.

For everyday spoken European Portuguese, the original version is the most natural.

Why is “arrumar” in the infinitive form? Could we use another tense like “arruma”?

After por in this structure, the verb must stay in the infinitive:

ser responsável por + infinitive
- é responsável por arrumar ✅
- not é responsável por arruma ❌

If you want to use arruma, you must change the structure:

Em casa, cada um arruma o seu quarto. ✅
- At home, each one tidies their room.
- Here arruma is the main verb, not part of “é responsável por…”.

So both are correct, but:

“é responsável por arrumar” = focuses on responsibility
“arruma o seu quarto” = focuses on the action itself

Is this sentence specifically European Portuguese, or would it also sound natural in Brazilian Portuguese?

The sentence is perfectly understandable in Brazilian Portuguese, but there are some stylistic differences:

Use of the article with possessives:
- EP: o seu quarto (article almost always present)
- BP: seu quarto is also common, especially in some regions and registers.
Pronoun use:
- In Brazil, seu is often avoided in speech because of ambiguity, and people prefer:
  - o quarto dele / dela (his/her room).

Natural Brazilian-style variants could be:

Em casa, cada um é responsável por arrumar o seu quarto. (as-is, still fine)
Em casa, cada um é responsável por arrumar o próprio quarto.
Em casa, cada um é responsável por arrumar o quarto. (context gives the meaning)

For European Portuguese, the given sentence is completely standard and typical.