Learn Hardcore Russian: Когда брат начинает танцевать, его смех слышно во всём доме. - When my brother starts dancing, his laughter can be heard throughout the whole house.

Брат is the grammatical subject of the verb начинает (starts/begins).
In Russian, the subject of a finite verb normally stands in the nominative case, so брат must be nominative, not брата or any other form.

Structure of the first clause:

Когда – when
брат – brother (subject, nominative)
начинает – starts/begins (3rd person singular)
танцевать – to dance (infinitive, what he starts doing)

So the core is брат начинает – the brother starts; that’s why nominative is used.

Why is the verb after когда in the present tense (начинает) and not future (начнёт)?

Here начинает in the present tense expresses a general / repeated situation: whenever / every time my brother starts dancing…

Russian often uses the present tense with когда for:

general truths or habits:
- Когда идёт дождь, я беру зонт. – When it rains, I take an umbrella.
regular or typical behaviour:
- Когда брат начинает танцевать, … – Whenever he starts dancing, …

If you mean one specific moment in the future, you would usually use the future:

Когда брат начнёт танцевать, его смех будет слышен во всём доме.
– When (at that future moment) my brother starts dancing, his laughter will be heard throughout the whole house.

So:

Начинает – habitual, general, “whenever”.
Начнёт – one particular future moment.

Why do we use the infinitive танцевать after начинает instead of a finite verb like танцует?

Russian normally uses начинать / начать (to begin) with an infinitive to show what action is beginning:

начинать + infinitive = to start doing something
- начинает танцевать – starts to dance
- начала читать – (she) started to read
- начали работать – (they) started to work

Using танцует would describe the action itself, not the start of it:

Когда брат танцует, его смех слышно во всём доме.
– When my brother is dancing, his laughter can be heard…

So:

начинает танцевать – focuses on the moment of starting.
танцует alone – focuses on the activity (he is dancing).

Both are grammatically correct, but they mean slightly different things.

What is the difference between когда брат начинает танцевать and когда брат танцует?

They are both grammatically correct, but the nuance is different:

Когда брат начинает танцевать…
Focus: the moment he starts dancing.
Implies that as soon as he begins, something happens (in this case, laughter is heard).
Когда брат танцует…
Focus: the time while he is dancing in general.
Means whenever he is dancing.

In practice:

If you want to highlight the trigger moment (the start of the dance causes laughter), use начинает танцевать.
If you just mean “whenever he dances”, without stressing the beginning, танцует is fine.

Why do we say его смех instead of something with a verb like он смеётся?

Russian often uses a noun for actions or sounds where English uses a verb:

его смех – his laughter
он смеётся – he is laughing / he laughs

In this sentence, его смех acts as a thing (a sound) that can be heard:

его смех слышно – his laughter is audible

If we used он смеётся, we would need a different structure:

Когда брат начинает танцевать, его слышно во всём доме, когда он смеётся.
(clumsy and repetitive)

Or:

Когда брат начинает танцевать и смеётся, его слышно во всём доме.
– When my brother starts dancing and laughing, he can be heard throughout the whole house.

The original uses его смех because it fits well with impersonal слышно: it talks about the sound (his laughter), not the person acting.

What exactly is слышно? Is it a verb? Why is it neuter?

Слышно is not a normal verb; it is a so‑called category-of-state word (predicative adverb), used in impersonal constructions. It roughly means “(it is) audible”, “one can hear”.

Examples:

Его смех слышно. – His laughter can be heard.
Ничего не слышно. – Nothing can be heard.
Музыку было слышно издалека. – The music could be heard from far away.

It has a fixed neuter form because the sentence is grammatically impersonal: there is no grammatical subject that it needs to agree with (no it is). That’s why слышно stays in that form regardless of what is heard:

его смех слышно
их крики слышно
шум моря слышно

The neuter form here is not about gender agreement; it’s just the way these impersonal predicative words are formed.

Could we say его смех слышен во всём доме instead of его смех слышно во всём доме?

Yes, его смех слышен во всём доме is grammatically correct and natural.

Difference in nuance:

его смех слышно во всём доме
– more neutral / conversational, impersonal; very common in speech.
его смех слышен во всём доме
– uses the short-form adjective слышен, feels a bit more bookish or stylistic, and is a personal construction:
- subject: его смех
- predicate: слышен

Meaning-wise, they both say that his laughter can be heard throughout the whole house. In everyday conversation, слышно is probably more frequent.

Why do we say во всём доме instead of в всём доме?

Russian has two forms of the preposition в:

в
во

Во is used mainly:

Before consonant clusters that are difficult to pronounce after “в”, such as в + вс…
- во всём (instead of в всём)
- во всех (instead of в всех)
Sometimes for rhythm or euphony in set phrases:
- во сне (in one’s sleep)
- во время (during)

So во всём доме is chosen to avoid the awkward sequence в вс (two в in a row).

Why is it во всём доме and not во весь дом?

Во всём доме and во весь дом have different grammar and meaning:

Во всём доме
- во
  - всём доме (prepositional case)
- Literally: in all the house / throughout the whole house
- Emphasises location / space inside: everywhere in the house you can hear it.
во весь дом
- во
  - весь дом (accusative)
- Idiomatic: “as loud as the whole house”, “so that the whole house hears”
- Emphasises volume / scale of the sound, somewhat more figurative.

In your sentence, во всём доме is the more straightforward way to say “throughout the whole house (everywhere in it)”.

What case is во всём доме, and how is it formed?

It is in the prepositional case, used with в/во to indicate location in / at / on.

дом (house) – nominative singular
о доме, в доме – prepositional singular: доме

For весь дом (the whole house):

Masculine nominative: весь дом
Masculine prepositional: во всём доме

So the phrase во всём доме breaks down as:

во – in
всём – prepositional singular of весь (whole)
доме – prepositional singular of дом

Literally: in the whole house.

Why is it всём with ё, not всем with е?

Grammatically, the correct form is всём (with the sound ё), the prepositional singular of весь:

весь – nominative masculine singular (whole)
всего́ – genitive
всему́ – dative
все́м / во всём – prepositional (pronounced with ё: [фсʲом])

In ordinary writing, native speakers often don’t type the two dots and just write всем, but it is still pronounced with ё: [фсʲом], not [фсʲем].

So во всём доме is pronounced vo vsyom dóme, even if you see it printed as во всем доме.

Could we drop его and just say смех слышно во всём доме?

Yes, grammatically you can say:

Смех слышно во всём доме. – Laughter can be heard throughout the whole house.

However, you would then lose the information “his”. The original sentence connects the laughter specifically with the brother:

его смех – his laughter (the brother’s)

If the context already makes it absolutely clear whose laughter you are talking about, смех слышно во всём доме can be fine. But normally you’d keep его to avoid ambiguity.

Can we change the word order to Его смех слышно во всём доме, когда брат начинает танцевать?

Yes, this word order is grammatically correct. Russian word order is relatively flexible, and both are possible:

Когда брат начинает танцевать, его смех слышно во всём доме.
Его смех слышно во всём доме, когда брат начинает танцевать.

The difference is mainly what is highlighted:

Version 1 first sets the condition / time: When he starts dancing…
Version 2 first emphasises the result / main fact: His laughter can be heard throughout the whole house…

In speech, intonation will also influence what feels more prominent, but both are natural.

Why is there a comma before его смех слышно?

The sentence consists of two clauses:

Когда брат начинает танцевать – subordinate clause (time, introduced by когда)
(то) его смех слышно во всём доме – main clause

In Russian, a subordinate clause introduced by когда is separated from the main clause by a comma, regardless of the order:

Когда он приходит, я ухожу.
Я ухожу, когда он приходит.

So the comma marks the boundary between the когда-clause and the main clause его смех слышно во всём доме.

Is когда here “when” or “whenever”? How should I understand it?

With the present tense (начинает) and without any specific time expression, когда here naturally means “whenever / every time when”:

Когда брат начинает танцевать, его смех слышно во всём доме.
≈ Whenever my brother starts dancing, his laughter can be heard throughout the whole house.

If you wanted a single specific future event, you’d more likely use the future tense:

Когда брат начнёт танцевать, его смех будет слышно во всём доме.
– When (on that future occasion) my brother starts dancing…

So in the given sentence, think of когда as “whenever” in English, even though the literal word is “when”.