Learn Hardcore Polish: Mój brat ćwiczy na gitarze, a jego koleżanka gra na pianinie. - My brother practises on the guitar and his friend plays the piano.

grać (na czym?) – to play (an instrument)
- Mój brat gra na gitarze. – My brother plays the guitar / is playing the guitar.
  Neutral; just says that he plays.
ćwiczyć (na czym?) – to practise (on an instrument)
- Mój brat ćwiczy na gitarze. – My brother is practising on the guitar.
  Focus on practice, training, improving skills.

So yes, you could say:

Mój brat gra na gitarze, a jego koleżanka gra na pianinie.

That would mean: My brother plays the guitar and his friend plays the piano (simply describing what each one plays).

The original sentence with ćwiczy na gitarze suggests he’s currently practising or working on his skills, while she is (simply) playing the piano.

Why do we say na gitarze and na pianinie? Why not just gitarę or pianino?

With musical instruments, Polish normally uses the pattern:

grać / ćwiczyć na + [locative case]

Examples:

grać na gitarze – to play the guitar
ćwiczyć na pianinie – to practise on the piano
grać na skrzypcach – to play the violin
grać na trąbce – to play the trumpet

So:

na gitarze – “on the guitar” (locative of gitara)
na pianinie – “on the piano” (locative of pianino)

Using just gitarę or pianino without na would sound wrong in this context.
You might see other verbs that can take a direct object:

uczyć się gry na gitarze – to learn (the) guitar playing
opanuję gitarę – I’ll master the guitar

…but with grać and ćwiczyć for instruments, the idiomatic construction is na + locative.

What case is gitarze and pianinie, and why do they change their endings?

Both gitarze and pianinie are in the locative case (Polish: miejscownik), used mainly after certain prepositions, including na in the “on/at” sense used here.

gitara (feminine noun)
- nominative (dictionary form): gitara
- locative singular: gitarze
  → na gitarze
pianino (neuter noun)
- nominative: pianino
- locative singular: pianinie
  → na pianinie

So the pattern is:

na + locative → na gitarze, na pianinie

The case is required by the preposition na in this meaning (“on/at” as in playing an instrument), not by the verb itself.

Why is it Mój brat and not Moja brat?

Possessive adjectives in Polish agree with the gender of the noun they describe.

brat (brother) is masculine, so we use:
- mój brat – my brother

The basic forms of “my” are:

mój – masculine (e.g. mój brat, mój telefon)
moja – feminine (e.g. moja siostra, moja książka)
moje – neuter (e.g. moje dziecko, moje okno)

So you’d say:

Mój brat – my brother
Moja siostra – my sister
Moje dziecko – my child

What exactly does jego koleżanka mean? Is koleżanka “friend”, “classmate”, or something else?

koleżanka is a common but slightly tricky word to translate. It usually refers to a female peer from some shared context:

a classmate (from school)
a colleague (from work)
a teammate (from a club, group, etc.)
or just a general female acquaintance / friend

It often sounds less close/intimate than przyjaciółka:

przyjaciółka – (close) female friend
koleżanka – female colleague / friend / acquaintance

In practice, koleżanka is very commonly used for “female friend”, especially when you don’t want to suggest a deep emotional bond.

So jego koleżanka = his (female) friend / classmate / colleague, depending on context.

Does jego change for gender or case, like mój / moja / moje?

No. jego (“his”) is invariable – its form does not change for gender, number, or case.

Compare with mój / moja / moje:

mój brat – my brother (masc.)
moja koleżanka – my (female) friend (fem.)
moje dziecko – my child (neut.)

But with jego:

jego brat – his brother
jego koleżanka – his (female) friend
jego dziecko – his child

All are jego, regardless of gender.

Even in other cases, jego stays the same:

Widzę jego brata. – I see his brother.
Rozmawiam z jego koleżanką. – I’m talking with his friend.

Spoken Polish sometimes shortens it to go after a preposition or verb (e.g. widzę go = “I see him”), but jego as a possessive stays unchanged.

Why is the conjunction a used, and not i? Don’t they both mean “and”?

Both i and a can be translated as “and”, but they have different nuances:

i – neutral “and”, simply adding things together
- Mój brat gra na gitarze i śpiewa. – My brother plays the guitar and sings.
a – “and” with a sense of contrast or difference between two clauses
- Mój brat ćwiczy na gitarze, a jego koleżanka gra na pianinie.
  → My brother is practising on the guitar, whereas his (female) friend is playing the piano.

So a here suggests a mild contrast: he is practising the guitar, but she is (just) playing the piano. In English you could translate it as “and” or “while/whereas” depending on the style:

“My brother is practising the guitar, and his friend is playing the piano.”
“My brother is practising the guitar, whereas his friend is playing the piano.”

Why are both verbs in simple present (ćwiczy, gra)? In English I’d probably say “is practising” and “is playing”.

Polish does not have a separate continuous (“-ing”) tense like English.
The present tense usually covers both:

English simple present:
- On gra na pianinie. – He plays the piano.
English present continuous:
- On gra na pianinie. – He is playing the piano (now).

Context tells you whether it’s a habit or a current, ongoing action.

In this sentence:

Mój brat ćwiczy na gitarze, a jego koleżanka gra na pianinie.

it naturally sounds like a current situation (what they are doing now), but grammatically it’s just the regular present tense.

If you really want to emphasise “right now”, you can add a time expression:

Teraz mój brat ćwiczy na gitarze… – Right now my brother is practising on the guitar…

Could I say Mój brat gra na gitarze, a jego koleżanka ćwiczy na pianinie instead? Would it change the meaning?

Yes, that sentence is perfectly correct, but the nuance changes:

Mój brat ćwiczy na gitarze, a jego koleżanka gra na pianinie.
→ He is practising on the guitar, while she is simply playing the piano.
Mój brat gra na gitarze, a jego koleżanka ćwiczy na pianinie.
→ He is (just) playing the guitar, while she is practising on the piano (working on her skills).

So swapping ćwiczy and gra moves the focus of “practising” from him to her. Grammatically both sentences are fine; it’s just a question of what you want to emphasize.

Is the word order fixed? Could I say Na gitarze mój brat ćwiczy, a na pianinie gra jego koleżanka?

Polish word order is fairly flexible, especially compared to English. Your alternative:

Na gitarze mój brat ćwiczy, a na pianinie gra jego koleżanka.

is grammatically correct, but it has a different emphasis:

Mój brat ćwiczy na gitarze…
Neutral order; focus on “my brother” and what he does.
Na gitarze mój brat ćwiczy…
Emphasises na gitarze (“on the guitar”), e.g. contrasting with another instrument:
- Nie na skrzypcach, na gitarze mój brat ćwiczy. – Not on the violin, on the guitar my brother practises.

In ordinary, neutral sentences, learners are usually safest with:

[Subject] + [Verb] + [Rest of the sentence]
→ Mój brat ćwiczy na gitarze…

Why isn’t there a reflexive form like ćwiczy się here?

The verb ćwiczyć can be:

transitive – take a direct object:
- Ćwiczę polski. – I’m practising Polish.
- Ona ćwiczy jogę. – She practises yoga.
or intransitive, with a prepositional phrase:
- Ćwiczę na gitarze. – I’m practising on the guitar.
- On ćwiczy na pianinie. – He practises on the piano.

The reflexive form ćwiczyć się exists, but it usually means to train oneself, often physically or in a general sense:

On dużo ćwiczy się na siłowni. – He trains a lot at the gym.

With musical instruments, the most natural options are:

ćwiczyć na gitarze / na pianinie
ćwiczyć grę na gitarze – to practise guitar playing (more formal / explicit)

So ćwiczy na gitarze is the standard, idiomatic form here; ćwiczy się na gitarze would sound odd.

How do you pronounce tricky words like ćwiczy, koleżanka, and pianinie?

Some pronunciation tips:

ćwiczy [CHVEE-chih]
- ć – soft “ch” sound, like “tch” but softer, tongue closer to “cheese” than “church”.
- wi – like English “vee”.
- stress on the first syllable: ĆWI-czy.
koleżanka [ko-le-ZHAN-ka]
- rz – usually pronounced like ż, similar to the “s” in “measure”.
- stress on -żan-: ko-le-ŻAN-ka (actually second-to-last syllable: koleŻANka).
pianinie [pya-NEE-nye]
- pia- – like “pya-” (softened p + ya).
- -nie – “nyeh” (a soft n + e).
- stress on the second syllable: pia-NI-nie (again, penultimate syllable).

General rule in Polish: stress is almost always on the second-to-last syllable, which helps a lot once you know it.