Cooperative double

The direct double over RHO’s overcall over 1NT opening is cooperative. The other doubles are penalty.

The cooperative double is a blend between takeout and penalty doubles. This cooperative double requires not only 3–4 cards in each unbid suit like a takeout double but also 2–4 cards in the called suit to secure conversion to penalty with opener’s 3+ cards. Moreover, because penalty is expected, 4-3-3-3 is allowed.

This cooperative double shows 8+ points, i.e. invitational+ values. Probing Wbridge5 5.12 shows that it usually denies a stopper in the called suit. With a stopper, responder bids 3NT instead. The exception is the double of 3♠, which is more penal.

• As takeout: Opener can jump to game with maximum.
• As penalty: Defending pays even if opponents have an 8-card fit.

Opener often passes to convert the double to penalty. However, opener sometimes runs. Probing Wbridge5 5.12 over 2♥ shows that opener runs to a 3-level suit only with a doubleton ♥, while 5 spades run to 2♠ with 2–3 ♥. Opener occasionally runs to 2NT without a 5-card suit.

Not probed

• Opener’s call after the double of overcalls other than (2♥), and responder’s next call after opener runs.