Learn Hardcore Polish: Ich śmiech jest głośny, ale to miły hałas, kiedy cała rodzina gra razem na boisku. - Their laughter is loud, but it is a pleasant noise when the whole family plays together on the field.

If you said oni śmieją się, that would mean they are laughing (a whole different structure: subject + verb), not their laughter (possessive + noun).

So:

Ich śmiech jest głośny = Their laughter is loud.
Oni śmieją się głośno = They are laughing loudly.

Ich in its possessive use does not change its form (it’s the same regardless of gender or case), which is nice for learners.

What case is śmiech in, and why?

Śmiech is in the nominative singular.

In the sentence Ich śmiech jest głośny, the structure is:

ich śmiech – subject (nominative)
jest – verb
głośny – predicate adjective (also nominative, agreeing with the subject)

Polish uses the nominative for the subject of the sentence, so śmiech appears in its base dictionary form.

Why is it głośny and not głośno?

Because here głośny is an adjective describing a noun (śmiech), not an adverb describing a verb.

głośny = loud (adjective, used with nouns)
- głośny śmiech – loud laughter
- głośna muzyka – loud music
głośno = loudly (adverb, used with verbs)
- Oni śmieją się głośno. – They laugh loudly.
- On mówi głośno. – He speaks loudly.

In Ich śmiech jest głośny, the logic is:
Their laughter is [what kind?] → loud.
So you need the adjective form głośny.

Why do we say to miły hałas and not jest miłym hałasem?

Polish has a very common pattern:

To jest X. – This/that/it is X.

In everyday speech, with this pattern, jest is often dropped:

To jest miły hałas. → To miły hałas.

So to miły hałas is basically a shortened form of to jest miły hałas.

About your alternative jest miłym hałasem:

To jest miły hałas. – more neutral, simple identification: It is a pleasant noise.
Jest miłym hałasem. – also possible, but now “it” is understood from context; and miłym hałasem is in instrumental case because it’s the complement of być without to in front.

Here the writer chose the to jest X pattern (with jest omitted), which keeps miły hałas in the nominative.

Why is the pronoun to used, and not something agreeing with hałas?

In the structure To (jest) X, to is a kind of neutral demonstrative pronoun (like this/that/it), and it stays in the neuter form to regardless of the gender of X.

Examples:

To jest pies. – This/That is a dog. (pies – masculine)
To jest książka. – This/That is a book. (książka – feminine)
To jest dziecko. – This/That is a child. (dziecko – neuter)

The to does not agree in gender with the noun. It’s just a fixed form that introduces the identification.

So:

…ale to (jest) miły hałas… – but it is a pleasant noise…

What’s the nuance of miły hałas? Isn’t hałas normally something negative?

Yes, hałas usually has a negative feel: noise, racket.

By calling it a miły hałas (pleasant / nice noise), the sentence is deliberately a bit paradoxical or playful:

Normally: hałas = unpleasant, disturbing noise.
Here: the noise (their loud laughter, the family playing) is emotionally positive for the speaker, so they call it miły.

You could also say:

przyjemny hałas – pleasant noise
wesoły hałas – cheerful noise

But miły hałas is perfectly natural and emphasizes the warmth/affection the speaker feels toward this particular noise.

Why is it kiedy and not gdy in kiedy cała rodzina gra razem na boisku?

Both kiedy and gdy can mean when (in the sense of at the time that):

Kiedy cała rodzina gra razem na boisku, ich śmiech jest głośny.
Gdy cała rodzina gra razem na boisku, ich śmiech jest głośny.

In many contexts they’re interchangeable. Differences:

kiedy – more neutral, very common in speech.
gdy – slightly more formal or literary in many people’s perception, but still normal.

In this sentence, kiedy simply sounds very natural and conversational.

Why is it cała rodzina gra, not cała rodzina grają? In English we say the whole family play (plural) sometimes.

In Polish, rodzina (family) is grammatically singular feminine, so the verb usually agrees with it in the singular:

Rodzina gra. – The family plays.
Cała rodzina gra. – The whole family plays.

Even though rodzina refers to many people, grammatically it behaves like one unit.

You can sometimes hear plural agreement with collective nouns (e.g. rodzina grają), but:

It is much less common.
It sounds colloquial or non-standard in many contexts.

Standard, neutral Polish prefers:

Cała rodzina gra razem na boisku.

What is the role and typical position of razem here?

Razem means together and is an adverb.

In cała rodzina gra razem na boisku:

gra – plays
razem – together
na boisku – on the field

The default, natural position is right after the verb, but Polish word order is flexible. You could also say:

Cała rodzina razem gra na boisku.
Razem cała rodzina gra na boisku.

The differences in meaning are small; changes mainly affect rhythm/emphasis. The version given (gra razem na boisku) is the most neutral.

Why is it na boisku and not na boisko?

The preposition na can take either:

locative (where? – location), or
accusative (where to? – movement onto something).

Here we have where they play, so it’s a location:

grają na boisku – they play on the field (where?) → locative

Compare:

Idą na boisko. – They are going onto the field (where to?) → accusative
Są na boisku. – They are on the field (where?) → locative

So:

Nominative: boisko
Locative: (na) boisku

What is the declension pattern of boisko → boisku?

Boisko is a neuter noun ending in -o. Its singular forms (most important ones) are:

Nominative: boisko – a field, a pitch (dictionary form)
Genitive: boiska – of the field
Dative: boisku – to/for the field
Accusative: boisko – [same as nominative]
Instrumental: boiskiem – with the field
Locative: boisku – on/about the field
Vocative: (same as nominative) boisko

In na boisku, you see the locative form boisku.

In English we’d usually specify what game they play (e.g. play football). Why is it just gra na boisku in Polish?

Polish often omits the object when it’s obvious from context, especially with grać (to play):

Dzieci grają na boisku. – The children are playing on the field.
(Usually understood as playing some ball game, typically football/soccer.)

If you want to specify the sport, you can add it:

grać w piłkę (nożną) – to play football/soccer
grać w koszykówkę – to play basketball

Examples:

Cała rodzina gra razem w piłkę na boisku. – The whole family plays football together on the field.

The original sentence doesn’t need the sport named; the image of family + field + laughter is enough.

Why is there no word for the or a in this sentence?

Polish has no articles (no direct equivalents of English a/an or the).

The ideas that English expresses with articles are handled in other ways:

context
word order
pronouns (like ten, ta, to)
sometimes just left implicit

So:

Ich śmiech jest głośny can mean:
- Their laughter is loud (generic), or
- Their laughter is loud (in this particular situation)
cała rodzina can mean the whole family; the is just understood from context.

You only add something like ta rodzina (this/that family) when you specifically need that extra emphasis.