बिल्ली की हरकत तेज़ है।

to be

Breakdown of बिल्ली की हरकत तेज़ है।

• का: of
• तेज़: fast
• बिल्ली: cat

Questions & Answers about बिल्ली की हरकत तेज़ है।

Why is की used in बिल्ली की हरकत?

की is the genitive marker here, roughly like of or the English 's.

So:

• बिल्ली की हरकत = the cat's movement / action / behavior

A very important point: का / की / के agree with the noun that comes after them, not with the owner.

Here the following noun is हरकत, which is feminine singular, so Hindi uses की.

For comparison:

• बिल्ली का बच्चा = the cat's kitten
  
  • बच्चा is masculine singular, so का
• बिल्ली की हरकत = the cat's movement
  
  • हरकत is feminine singular, so की

Does की agree with बिल्ली or with हरकत?

It agrees with हरकत, not with बिल्ली.

This is one of the most common things English speakers need to get used to in Hindi. In English, we do not change 's depending on the noun after it, but in Hindi the possessive marker changes form:

• का for masculine singular
• की for feminine
• के for masculine plural and some other contexts

So in बिल्ली की हरकत, the key reason for की is that हरकत is feminine.