Learn Hardcore French: Paul est très poli avec sa colocataire, mais sa sœur peut être un peu impolie. - Paul is very polite with his roommate, but his sister can be a bit impolite.

Here the adjective describes sa sœur, which is feminine singular (une sœur).
So the adjective must also be feminine singular: impolie (with -e at the end), not impoli.

Why do we use sa both for sa colocataire and sa sœur, even though Paul is male?

In French, mon / ma / mes, ton / ta / tes, son / sa / ses agree with the thing possessed, not with the owner.

sa colocataire → colocataire is feminine here
sa sœur → sœur is feminine

So we use sa (feminine singular) both times, even though the owner (Paul) is male.

What gender is colocataire, and how can I tell in this sentence?

Colocataire is an epicene noun: the spelling is the same for masculine and feminine.
You see the gender from the determiner:

son colocataire = his/her male roommate
sa colocataire = his/her female roommate

Here it’s sa colocataire, so the roommate is female.

Why is it avec sa colocataire and not envers sa colocataire?

Avec literally means with and is very common when talking about how you behave with someone.

Envers is closer to towards in English and is a bit more formal or written style. You could say poli envers sa colocataire, but poli avec sa colocataire is more neutral and natural in everyday speech.

What is the difference between peut être (two words here) and peut-être (with a hyphen)?

Peut être (two words) = can be (verb peut
- infinitive être)
- sa sœur peut être un peu impolie = his sister can be a bit impolite.
Peut-être (with hyphen) = maybe / perhaps (an adverb)
- Peut-être sa sœur est un peu impolie = Maybe his sister is a bit impolite.

They are pronounced almost the same but have different roles and spellings.

Could we say sa sœur est un peu impolie instead of peut être un peu impolie? What’s the nuance?

Yes, sa sœur est un peu impolie is grammatically correct.

peut être un peu impolie = can be a bit impolite → it’s not always; sometimes she behaves that way.
est un peu impolie = is a bit impolite → a more constant trait of character.

So peut être softens the statement and makes it less absolute.

Why is there no article like la before sœur, as in sa sœur instead of la sœur de Paul?

You normally use a possessive (sa, son, ses) instead of a definite article (le, la, les) when you say someone’s [family member/body part/etc.]:

sa sœur = his/her sister
la sœur de Paul = Paul’s sister

Both are correct, but sa sœur is shorter and more natural when the possessor is already clear from the context (here, Paul).

Can we change the position of très and un peu? For example, can we say Paul est poli très or peut être impolie un peu?

No, you can’t move them like that. In French, adverbs like très and un peu usually go directly before the adjective:

est très poli (not est poli très)
un peu impolie (not impolie un peu in this short phrase)

The neutral pattern is: verb + adverb + adjective or adverb + adjective.

What is the difference between impoli(e) and malpoli(e)?

They are very close in meaning and often interchangeable:

impoli(e) = impolite, not polite
malpoli(e) = also impolite, literally badly polite

Malpoli can sound a bit stronger or more informal in some contexts, but both are common for describing rude or badly mannered behavior.

Why is the conjunction mais used here, and could I use par contre instead?

Mais = but and is the standard conjunction to introduce a contrast between two clauses: poli… mais… impolie.

You could say …avec sa colocataire, par contre sa sœur…, but par contre works more like on the other hand and is often placed after a pause. Mais is simpler and more neutral in this sentence.

How do you pronounce the liaisons in Paul est très poli? Are there any?

There is usually one liaison:

Paul est très poli → /pɔl‿ɛ tʁɛ pɔli/
- Liaison between Paul and est: Paul est → pɔl‿ɛ (the final l of Paul is linked to est).
- No liaison between très and poli: you say trè poli, not trè-z-poli.

So you link Paul and est, but not très and poli.

Could I say sa coloc instead of sa colocataire?

Yes, sa coloc is a common informal shortening of sa colocataire, especially in speech and casual writing.

sa colocataire → neutral, standard
sa coloc → colloquial, familiar

Both refer to the roommate; choose depending on how informal you want to sound.