What if you had a bid at your fingertips that could do the following: Show a suit with exact length; allow you to bid two suits at once; show one suit with help for partner’s original suit; indicate a minimum number of high card points; allow you to bid a strong suit with an otherwise relatively weak hand (with no confusion to partner; and keep your partner out of trouble.

Wouldn’t that be a game changer?

Yes. So, let’s enter the world of the negative double.

The negative double is a useful convention and one you definitely want to have in your bidding tool box. It is a tool that is indispensable when coping with an opponent’s overcall.

Most players confuse it with a penalty double, and it’s important to know the difference between a negative double and a takeout double.

A negative double (ND) is used when your partner opens; a takeout double (TD) is used when an opponent opens.

The ND is made by the responder; a TD is made by the overcalling side; thus, the overcaller’s suit is doubled in a ND, but the opener’s suit is doubled in a TD.

You need six-plus points to make a ND at the one level (more at higher levels), but you need an opening hand to make a TD at the one level (more at higher levels).

The emphasis of a ND is on the unbid major(s), whereas the emphasis of the TD is on all of the unbid suits.

In a ND, you do not have to be short in the opponent’s suit, but in a TD you must be short in the opponent’s suit.

Finally, a ND followed by a bid in a new suit is weak; a TD followed by a bid in a new suit is strong (17 or more points).

In Marty Bergen’s book “Introduction to Negative Doubles,” he claims that the negative double is “the most important convention in modern bridge.” He said if he had to choose to give up Stayman or negative doubles, he would sooner give up Stayman.

Try a few exercises in which you need to know the negative double.

Your partner opened one club; the RHO (right-hand opponent) overcalled one spade. What is your bid? (Answers at end of column)

1. 96 KJ43 KJ8 J972

2. AQ3 KJ986 974 96

3. 876 QJ96 974 987

4. Q98 A4 KQJ J7643

5. 754 AK 64d3 AQ1098

Dr. Kathie Walsh, an ABTA teacher of the year, teaches all levels of bridge at Hilton Head Island Bridge Club. kbwalsh@roadrunner.com