General
When partner opens 1-Major and we play 2/1 GF, then a 1NT response is used with most hands that have minimum or invitational values without a fit, showing 6-11 points. A 2NT response to a Major suit opening is not used as a natural bid because it is Jacoby 2NT, showing game forcing values and at least 4-card support. So the question is what should a jump to 3NT in response to a 1-Major opening show?
1-Major – 3NT
A jump to 3NT after a 1-Major opening eats up a tremendous amount of bidding space. Bids that do this should be highly defined bids, giving partner a precise description of our hand. These types of bids are called picture bids.
1-Major – 3NT shows game forcing values, but not many more values than that, about 12-15 points. This jump to 3NT also shows a relatively flat hand with little interest in other games. Most partnerships play 1M – 3NT to show 2/3-4-4 distribution, with exactly 2-card support for Opener’s Major suit, and 12-15 HCP. This bidding sequence also shows a desire to be the declarer and a hand with at least some tenaces, because otherwise we can make a 2/1 GF bid first and see if partner wants to become the declarer by bidding Notrump.
Opener’s Rebid
After the auction begins 1M – 3NT, Opener can make use of the shape and strength information to choose to play in the game they think is best. Opener can pass if 3NT is where they think it is the best place to play, or opener can make a natural bid over 3NT to try for a different game contract.
Example 1
1♠ P 3NT P
__?
♠ AQ932
♥ A4
♦ K953
♣ 84
Pass 3NT with no Major suit fit.
Example 2
1♠ P 3NT P
__?
♠ AQ9732
♥ 84
♦ K53
♣ A4
With a 6-2 Major suit fit, correct the final contract to 4♠.
Example 3
1♠ P 3NT P
__?
♠ AQ932
♥ KJ753
♦ A8
♣ 4
With a 5-3 heart fit, correct the final contract to 4♥.
Four Cards in the Other Major
We do not want the Responder’s bid of 3NT to be ambiguous about having 3 or 4 cards in the unbid Major because this will leave Opener guessing whether the partnership has a 4-4 fit in the other Major. Thus, Responder’s jump to 3NT shows 2/3-4-4 distribution with exactly 4-cards in each minor suit. If Opener is 5/4 in the Majors, then Opener should know to pass 3NT, not look for a 4-4 fit in the other Major suit.
Bidding Slam After 1-Major – 3NT
With a powerful hand, Opener can try for slam
With no extra shape and a balanced 18-19 point hand, Opener can raise to 4NT to invite slam.
With a 6-card Major suit and extra values, Opener can jump to 5-Major to invite for slam.
With 5-5 in the Majors, Opener starts with 1♠ and after a 3NT response Opener jumps to 5♥ to invite slam.
With slam interest and a 4+card minor suit then Opener can bid 4-minor over partner’s 3NT response. Since 3NT was a game forcing bid, 4-minor is forcing and is a slam try; if Opener only wanted to play game then they would just jump to 5-minor.
Alternative Agreement
Some partnerships play 1M – 3NT as exactly 3-3-3/4 distribution, showing a fit and offering a choice of game for Opener between 3NT and 4♠.
Conclusion
1-Major – 3NT is not a common auction, but is a useful picture bid that completely describes the hand in one bid and lets partner make the choice of best game contract or make an effort to explore slam. After making this response, partner will normally pass. Though they can bid 4♠ or 4♥ or even a minor at the 5-level or 6-level.