The 2NT response to the unbalanced 1♦ opening bid
In Modern American bidding, our 1♦ opening bid promises at least 4 diamonds and unspecified shortness. If we don't have a singleton or void, then we will have at least 6 diamonds. This can be awkward for responder when they hold a balanced 13-15 HCP. If they can't bid a 4 card major or raise diamonds (inverted, forcing bid), how do they know 3NT is the correct contract? Typically, opener has a 3154 shape hand. If responder doesn't have a 4 card major, it is likely that opener's shortness in a major results in the opponents having 9 cards in that major. 3NT may be doomed if opponents can run off 5 tricks in the major. However, opener isn't guaranteed to have shortness in a major. They maybe have a 6 card diamonds suit and 322 remaining shape, they could have opened a 4441 hand. Additionally, opener may have above average values and will wonder if they can make a small slam. The crux is that jumping directly to 3NT closes out any chances to explore options toward a final contract.
We have defined in our responses to the Macaw 1♦ the jump bid of 2♥ to show a flat, balanced hand with 11-12 HCP to invite to a game. That frees up the jump bid of 2NT for our purposes. We can use the 2NT bid to show the same shaped hand as 2♥, but with more points. 13-15 HCP. This bid is forcing for at least one round. It's purpose to allow opener a vote in the 3NT game contract. Opener may be extremely wary of playing 3NT. Opener may also have interest in exploring for a small slam.
1♦ - 2NT: 13-15 HCP, denies a 4 card major, also denies 4 card diamond suit
Responses: (2NT cannot be passed)
- 3NT - This game is acceptable to me.
- 3
- 5-5 in minors and minimal (11-12 HCP) opening hand - 3
- 6 diamonds, no side shortness. Typical (11-14 HCP opening hand) - 3
/3
- 6 diamonds, this is my short suit (splinter). Decide if you want to play 3NT or 5♦ or try for small slam - 4 - 5-5 in minors and extra values (15+ HCP)
- 4 - 6 diamonds, slam values. This is Ace Asking (minorwood)
Once opener has chimed in with their hand, showing shape and strength, responder is in a good place to make a tactical decision on ultimate contract.
When opener shows a minimal two-suited hand, responder may (likely) feel comfortable reaching a 5♣ contract. If opener responds with 3♦, responder with an Honor XX in diamonds and reasonable control in the side suits will bid 3NT expecting to run the 6 diamond tricks. Responding to opener's strong responses is even easier. If opener is exploring slam, responder only has to describe their hand. This is usually by bidding their first round control suit. Additionally, they can bid 4♦ as minorwood, ace asking. So much flexibility, so much power in not closing out the auction with a direct jump to 3NT.