Breakdown of Затопление началось в подвале.
Questions & Answers about Затопление началось в подвале.
Because the verb is начаться — the perfective, intransitive verb meaning to begin / to start.
In the past tense, Russian verbs agree with the subject in gender and number. The subject here is затопление, which is neuter singular, so the past-tense form is:
- masculine: начался
- feminine: началась
- neuter: началось
- plural: начались
The -сь / -ся part is the reflexive ending that belongs to the verb начаться.
So:
- затопление началось = the flooding began
Because nouns ending in -ие are usually neuter in Russian.
So затопление is a neuter noun, and that is why the verb is also in the neuter past form началось.
A learner can often use the ending as a clue:
- -ие → often neuter
- -а / -я → often feminine
- consonant ending → often masculine
It is in the nominative case because it is the subject of the sentence.
In this sentence, the thing that began is затопление. So Russian uses the nominative:
- Затопление началось = The flooding began
If you changed the sentence so that flooding became the object, the case would probably change.