Here’s your hand sitting south:
Your partner, North, opens 1C. Here’s the bidding to you:
West North East South
1C 3H ?
You’ve got a terrific diamond suit and for all you know your partner might only have three little clubs and the AKQ are held by opponents, so you could lose two clubs and a heart, so a jump to 5C is not the best bid for two reasons; you might not make 5C and you might miss a slam. But a simple raise to four clubs doesn’t do justice to this hand. And to bid your diamond suit, which would be forcing, puts your partner in a bind if she opened with, let’s say distribution of 4-3-2-4. So what’s your call?
You have a perfect call, 4H! This is a cooperating call because you are a partnership and you should make decisions together, not unilaterally. This bid tells partner that you have a good hand with support for her suit. And if she goes to 5C, you have an easy call to six, thinking that you certainly won’t lose anything but a heart. You just have to hope that she’s got the AK of clubs. Sometimes you have to rely on instinct and take a chance.
Here's the four-hand layout:
♠ KQ752 ♠ 10963
♥ Q98 ♥ K1075432
♦ 1083 ♦ 52
♣ Q3 ♣ Void
This hand was played 13 times in a club game. Five played it in 5C. Four played it in 3N. Two played it in 5D. Two pairs found the club slam and played it in 6. All pairs made seven except one who somehow lost a trick and only made 6N.