Learn Hardcore Polish: Cicha muzyka wieczorem poprawia mi nastrój po długim dniu. - Quiet music in the evening improves my mood after a long day.

muzyka is a feminine, singular noun in the nominative case.
The basic (nominative singular) feminine form of the adjective cichy is cicha.

So you get:

cichy – masculine (e.g. cichy chłopak)
cicha – feminine (e.g. cicha muzyka)
ciche – neuter (e.g. ciche radio)

Because muzyka is feminine, the adjective has to be feminine too: cicha muzyka.

What case is muzyka in here, and what is its grammatical role?

Muzyka is in the nominative singular (mianownik, liczba pojedyncza).

In this sentence, cicha muzyka is the subject – it is the thing that performs the action of the verb:

Cicha muzyka (subject)
poprawia (verb)
mi nastrój (indirect + direct object)

So the subject stands in the nominative: (ta) cicha muzyka.

What exactly is wieczorem, and why is there no preposition before it?

Wieczorem is the instrumental singular form of wieczór (evening).

Polish often uses the instrumental case without a preposition to express “when” something happens, especially with parts of the day:

rano – in the morning (instrumental of ranek / fossilized form)
wieczorem – in the evening (instrumental of wieczór)
nocą – at night (instrumental of noc)

So wieczorem literally is “in the evening”, but it’s just one word, no preposition needed. The whole phrase:

Cicha muzyka wieczorem = Quiet/soft music in the evening…

You could also say wieczorem at the beginning:
Wieczorem cicha muzyka poprawia mi nastrój… – this puts a bit more emphasis on “in the evening”.

What does poprawia mi nastrój literally mean, and why is it mi and not mój?

Literally:

poprawia – “improves” (3rd person singular, present, imperfective)
mi – “to me / for me” (dative)
nastrój – “mood” (accusative)

So poprawia mi nastrój is literally:
“(it) improves my mood for me” → in natural English: “improves my mood”.

There are two common ways to say this in Polish:

poprawia mi nastrój – dative pronoun mi
poprawia mój nastrój – possessive adjective mój

Both are correct, but the nuance is slightly different:

poprawia mi nastrój
- Very natural, very common.
- Focuses on the person whose mood is improved (me) using the dative.
- Feels a bit more personal / colloquial.
poprawia mój nastrój
- Also correct and idiomatic.
- Feels a bit more neutral or explicit: “improves my mood”.

In practice, poprawia mi nastrój sounds a touch more “lived in” and conversational.

What is the difference between mi and mnie, and why is mi used here?

Both mi and mnie mean “me” in the dative (and/or accusative in some contexts), but:

mi is the unstressed / clitic form
mnie is the stressed / full form

General rules:

Use mi in the middle of a sentence, especially directly after the verb, when it’s not emphasized:
- On *mi pomaga.* – He helps me.
- Muzyka poprawia *mi nastrój.*
Use mnie when:
- You want to emphasize “me”, or
- It stands in a position where the clitic doesn’t sound right (e.g. at the beginning), or
- After a preposition.

Examples:

On pomaga *mnie, a nie jej. – He helps *me, not her. (emphasis)
Dla *mnie to ważne.* – For me this is important. (after a preposition)

In poprawia mi nastrój, mi is unstressed, right after the verb, so the clitic mi is the natural choice.

What case is nastrój in, and why does it look like the nominative?

Nastrój here is in the accusative singular (biernik, liczba pojedyncza).

The verb poprawiać (to improve) takes a direct object in the accusative:
- poprawia co? → nastrój (what? mood)

For masculine inanimate nouns, the accusative form often matches the nominative form:

Nominative: nastrój
Accusative: nastrój (same shape)

Compare with a masculine animate noun like chłopak (boy):

Nominative: Widzę chłopak. – incorrect
Accusative: Widzę chłopaka. – correct

So here nastrój is grammatically accusative but looks identical to the nominative.

Why is it po długim dniu and not something like po długi dzień? What case is that?

The preposition po normally takes the locative case when it means “after” in a time expression.

po
- locative długi dzień → po długim dniu

Breakdown:

dzień (day) – noun
- nominative: dzień
- locative: dniu (irregular stem change: dzień → dniu)
długi (long) – adjective
- nominative masculine: długi dzień
- locative masculine: długim dniu

So:

po długim dniu = after a long day
- po – after
- długim – locative masculine singular
- dniu – locative masculine singular

Using po długi dzień is grammatically incorrect; po requires the locative in this meaning.

Why is the verb poprawia in the present tense if this is a general, habitual statement?

In Polish, the present tense of an imperfective verb is used both for:

Actions happening right now, and
General, habitual, or repeated actions.

Poprawiać (imperfective) / poprawić (perfective) is an aspect pair:

poprawia (3rd person singular, imperfective) – “improves / is improving”
poprawi (3rd person singular, perfective) – “will improve (once, as a single result)”

In your sentence:

Cicha muzyka wieczorem poprawia mi nastrój…
– describes what usually or regularly happens: “Quiet/soft music in the evening improves my mood…”.

If you used poprawi, it would sound more like a single future event:

Jutro wieczorem cicha muzyka poprawi mi nastrój. – Tomorrow evening quiet music will improve my mood (that one time).

Is this word order fixed, or can I move wieczorem or po długim dniu around?

Polish word order is fairly flexible, especially for adverbials like time expressions. All of these are grammatically possible, with small differences in emphasis:

Cicha muzyka wieczorem poprawia mi nastrój po długim dniu.
– Neutral, the given version.
Wieczorem cicha muzyka poprawia mi nastrój po długim dniu.
– Slightly more emphasis on “in the evening”.
Cicha muzyka poprawia mi wieczorem nastrój po długim dniu.
– Still okay, but sounds a bit more cluttered; usually you’d keep wieczorem closer to the verb or the beginning/end of the clause.
Po długim dniu cicha muzyka wieczorem poprawia mi nastrój.
– Emphasizes “after a long day” as the setting.

What you generally don’t do is split very tightly bound elements in a strange way, like putting wieczorem between mi and nastrój:

✗ Cicha muzyka poprawia mi wieczorem nastrój – understandable, but feels a bit odd; not wrong, just less natural than other options.

So you can move wieczorem and po długim dniu quite freely for focus and rhythm, as long as you don’t create very unnatural splits.

Does cicha muzyka mean “quiet music” or “soft music”? Would spokojna muzyka work here?

Literally, cicha muzyka is “quiet music”, but in natural English we usually say “soft music” or “quiet, soft music” for the same idea. In Polish:

cicha muzyka
- low volume, not loud
- often also carries a feel of being gentle or not disturbing
spokojna muzyka
- “calm music”, “relaxing music”
- describes the character of the music, not the volume
- it could in theory be played loudly, but usually we imagine it as relaxing.

Both fit this sentence well, just with slightly different shades of meaning:

Cicha muzyka wieczorem poprawia mi nastrój…
– Soft / quietly played music in the evening improves my mood…
Spokojna muzyka wieczorem poprawia mi nastrój…
– Calm / relaxing music in the evening improves my mood…

You can also combine them:
Cicha, spokojna muzyka wieczorem poprawia mi nastrój po długim dniu. – Quiet, calm music…