Use 'whose' to provide information about someone using their possessions.
Sarah is a businesswoman whose company is very famous.
- The businesswoman whose book recently became a bestseller is now rich.
- The family whose house was flooded lost many of their possessions.
Use 'whom' to provide information about a person that is the object of the clause.
This is the farmer whom I buy milk from.
Notice that 'whom' is 'who' with an 'm' at the end. This is similar to how the object forms of 'he' ('him') and 'they' ('them') also end in 'm'.
- Bob, whom you just spoke to, is my neighbor.
- The criminal whom you are talking about has been arrested.
Native speakers usually do not say 'whom' in casual speech. They say 'who'/'that' or simply omit 'whom':
- Formal: He's the chef whom I respect.
- Casual: He's the chef who/that I respect.
- Casual: He's the chef I respect.
However, 'whose' cannot be replaced or omitted.
