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

When my brother starts dancing, his laughter can be heard throughout the whole house.

Breakdown of Когда брат начинает танцевать, его смех слышно во всём доме.

• дом: the house
• брат: the brother
• когда: when
• его: his

Questions & Answers about Когда брат начинает танцевать, его смех слышно во всём доме.

Why is брат in the nominative case here?

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.

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