- (obsolete) A violent and peremptory procedure without any assigned reason; a sudden conclusive happening.
- Why is that not true?
- I don't want to go out today. — Why not?
- Used to state that one has no objection to and approves of a proposal.
- Let's have pizza for lunch. — Yes, why not?
- Used to introduce a proposal.
- Why not try turning the handle in the other direction to see if that opens the window?