Learn Hardcore Polish: Dzieci rzucają kostką i śmieją się, gdy gra planszowa jest dłuższa niż film. - The children throw the die and laugh when the board game is longer than the movie.

Literally, you might expect rzucać (to throw) + accusative, so rzucają kostkę. That is grammatically possible and would mean “they are throwing the die.”

However, the idiomatic Polish expression for rolling a die in a game is:

rzucać kostką – using the instrumental case.

Here kostką (instrumental singular of kostka) expresses the means or tool of the action: they are throwing *with a die. In English we don’t usually say *throw with a die, but in Polish this instrumental construction became the fixed phrase for game context.

So:

rzucać kostką – standard, idiomatic: “roll a die”
rzucać kostkę – grammatically OK, but sounds more literal/physical: “throw a die (as an object)”, less like game jargon.

Why is it kostką (singular), when in English we usually say dice (plural)?

Polish distinguishes clearly between one die and several dice:

jedna kostka – one die
dwie / trzy / cztery kostki – two / three / four dice
rzucać kostką – to roll a die
rzucać kostkami – to roll dice (more than one), here kostkami is instrumental plural

English everyday speech often uses dice even for a single die; Polish does not do this. In this sentence, kostką is singular and instrumental, so it corresponds to with a die / with one die, even though in practice games may use more than one.

The phrase rzucać kostką is a fixed, idiomatic way to talk about the activity in board or dice games, regardless of the exact number of physical dice on the table.

What is the się in śmieją się and why do we need it?

Śmiać się is a reflexive verb in Polish and it always appears with się:

śmiać się – to laugh
oni się śmieją / oni śmieją się – they are laughing

Się itself does not translate directly into English here; it’s just part of the verb. Many Polish verbs are reflexive where English is not:

uczyć się – to learn
bać się – to be afraid
spieszyć się – to be in a hurry

Word order with się is flexible:

Dzieci śmieją się – normal, neutral
Dzieci się śmieją – also correct, slightly different rhythm

But się must be present; Dzieci śmieją is ungrammatical.

What is the difference between gdy and kiedy? Could I say kiedy here instead of gdy?

Both gdy and kiedy can mean when (in the temporal sense), and in this sentence they are interchangeable:

… śmieją się, gdy gra planszowa jest dłuższa niż film.
… śmieją się, kiedy gra planszowa jest dłuższa niż film.

Both are correct.

Typical nuances:

kiedy is more colloquial and very common in everyday speech.
gdy is slightly more formal or literary, and often used in written language, stories, descriptions, etc.

In many contexts you can freely switch them without changing meaning. Here, gdy simply sounds a bit more “bookish,” but not strange.

Why is it gra planszowa, not planszowa gra?

In Polish, the usual order is adjective + noun:

czerwona książka – red book
długi film – long film

So you might expect planszowa gra for board game. Grammatically, planszowa gra is possible, but:

gra planszowa is the fixed, idiomatic collocation in Polish for board game.

This happens quite often with multi‑word terms where one noun + adjective combination becomes a set phrase and prefers one order:

piwo jasne (light beer) vs jasne piwo – both possible, but one may be more idiomatic in certain contexts
kawa rozpuszczalna (instant coffee) – fixed term

So you should learn gra planszowa as the standard way to say “board game.”

Why is it dłuższa, not dłużej?

Both come from długi (long), but they are different parts of speech:

dłuższy / dłuższa / dłuższe – comparative adjective forms (longer)
dłużej – comparative adverb (for a longer time / longer in duration)

In the sentence:

gra planszowa jest dłuższa niż film

we are describing the game (a noun), so we need an adjective that agrees with gra.

If we used trwać (to last), we would use the adverb:

Gra planszowa trwa dłużej niż film. – The board game lasts longer than the film.

So:

jest dłuższa – is longer (adjective, agrees with gra)
trwa dłużej – lasts longer (adverb, modifies trwa)

Why is dłuższa in the feminine form?

In Polish, adjectives agree with the noun in:

gender
number
case

The noun gra (game) is:

feminine
singular
nominative (subject of jest)

So the adjective must be:

feminine, singular, nominative: dłuższa

Examples of agreement:

gra jest długa / dłuższa – the game is long / longer (feminine)
film jest długi / dłuższy – the film is long / longer (masculine)
zadanie jest długie / dłuższe – the task is long / longer (neuter)

That’s why the sentence uses dłuższa and not dłuższy or dłuższe.

Why is it dłuższa niż film and not something like dłuższa od filmu? Are both correct?

Polish has two common ways to form comparisons with adjectives:

Adjective + niż + noun (same case)
This is what you see in the sentence:
- gra planszowa jest dłuższa niż film
Here, both gra planszowa and film are in the nominative.
Adjective + od + genitive noun
This is also very common:
- gra planszowa jest dłuższa od filmu
Here, filmu is genitive (of film).

Both are correct and natural here. In casual speech, od + genitive might be a bit more frequent, but niż is perfectly standard and maybe slightly more “textbook style.”

So you can say:

Ta gra jest dłuższa niż film.
Ta gra jest dłuższa od filmu.

Same meaning: longer than the film.

Why is film left at the very end of the sentence? Could you change the word order?

Polish word order is relatively flexible. The given version:

… gdy gra planszowa jest dłuższa niż film.

is the most neutral and natural: subject – verb – adjective – comparison.

You could, in theory, rearrange some parts, but many alternatives would sound unnatural or marked. For example:

… gdy gra planszowa jest dłuższa niż film – neutral
… gdy gra planszowa jest, niż film, dłuższa – wrong / unnatural
… gdy gra planszowa, niż film, jest dłuższa – very odd

In the comparison X jest dłuższy niż Y, Y (here film) almost always comes directly after niż, so it naturally ends up near the end of the clause.

Why is rzucają (present tense) used here, not a future form or something like rzucą?

In Polish, the present tense of an imperfective verb (like rzucać) is used not only for actions happening “right now” but also for:

general truths
habits
repeated actions

The sentence describes what children do in a typical / repeated situation:

Dzieci rzucają kostką i śmieją się, gdy…
– Children (typically) roll the die and laugh when…

Using rzucą (future, perfective) would imply a single, completed action in the future, which doesn’t fit the intended “whenever this happens, they do this” meaning.

So rzucają + śmieją się correctly express a habitual or repeated behavior.