Я живу во втором доме.

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Breakdown of Я живу во втором доме.

• дом: the house
• жить: to live
• второй: second

Questions & Answers about Я живу во втором доме.

Why is it во втором and not в втором?

Russian often adds о to в to make pronunciation easier before certain consonant clusters.

You use во instead of в mainly:

• before words starting with вт-, фл-, вс- etc.:
  во втором, во флаконе, во всём
• before some words starting with в where в в- would be hard to pronounce:
  во время instead of в время

So в втором is theoretically understandable but sounds awkward; во втором is the normal, natural form.

What case is во втором доме, and why is that case used?

Both втором and доме are in the prepositional case singular.

• The preposition в / во with the meaning “inside / at a location” is followed by prepositional:
  • в доме – in the house
  • в школе – at school
  • в городе – in the city

This sentence describes where someone lives (location, not movement), so you need the prepositional case: во втором доме.

Why is it втором and not второй?