You want to let your partner know that you have values, but you do not have a clear cut bid to make.
The answer is to use Responsive Doubles. The use of the bid is always logical, as a penalty double would just not make sense.
1. Your LHO bids a minor and your partner doubles and RHO raises,
a DOUBLE by you is now a responsive X and shows the major suits at least 4-4
1♣ X (part) 2/3/4♣ X = responsive
1♦ X (part) 2/3/4♦ X = responsive
2♦(weak) X (part) 3/4♦ X = responsive
3♦ X (part) 4♦ X = responsive
2♥(weak) X (part) 3♥ X = responsive
2♠(weak) X (part) 3♠ X= responsive
2. Your LHO bids a major and your partner doubles and RHO raises, a double by you shows the minors suit at least 4-4. You would have shown a Spade suit if you had it
1♥ X (part) 2/3♥ X= responsive
1♠ X (part) 2/3♠ X = responsive
- If your LHO bids a suit and your partner overcalls and RHO raises, a
double by you shows the unbid suits, at less 5-5 and at least 9 points (in the 2 suits preferably)
1♣ 1♦ 2♣ X = show 5-5 in the unbid suits
1♦ 1♥/♠2♣ 2♦ X = show 5-5 in the unbid suits
1♥ 1♠/2♣/♦
2♥ X = show 5-5 in the unbid suits
1♠ 2♣/♦/♥ 2♠ X = show 5-5 in the unbid suits
Note: If partner overcalls with a WJS the responsive X does not exist.
