A negative double is the name given to a double made by the responder. It promises support for the unbid suits and shows a hand where you don't have a natural bid to make. It means that you can take part in the auction safely even with quite a weak hand.
- 1-level = 6-9 HCP
- 2-level = 8-11 HCP
On the following hand you can't bid 1NT without a spade stopper. You need 10 HCP or more to change suit at the 2-level and you can't support partner.
The solution is to make a negative double. The message to partner is that you have some points, some length in the unbid suits, but not enough strength to bid at the 2-level.
Negative Double then Bid
Partner has opened and your right hand opponent has made an overcall.
Bidding a new suit at the 2 level as responder is forcing. How can you show your long suit without partner blasting off too high? You can make a negative double and then bid your suit to show length but no real interest in game.