Strong Balanced Hands
The main thing that will take tricks with balanced hands (4-3-3-3, 4-4-3-2, 5-3-3-2) is high card points, as there's not much shape to develop long suits and to trump shortages. Now the number of points you show partner must be accurate because they will add theirs to yours and decide whether a slam is possible. Slams in no trumps require a full 33 points for the small slam (6NT) and 37 for the grand slam (7 NT). Because there are no long suits, you really need plenty of points.
So when a balanced hand is too strong to open at the one-level, because you wouldn't like partner to pass with fewer than six points, open either 2NT or 2♣ and follow that up with a bid of no trumps. Most people have only one bid to describe their game forcing hands, and that's 2♣. The hand may or may not contain clubs.
So, for strong balanced hands
20-21: Open 2NT
22-24: Open 2♣ planning to rebid 2NT
25 +: Open 2♣ planning to rebid 3NT
Going to 6NT (or 7NT) will depend on the combined high card points because neither hand will have a long suit. Blackwood is not used here; instead, quantitative bids ask whether the strong hand is minimum or maximum. NB: 2NT p 4NT is NOT the Blackwood convention. It is a quantitative raise, asking partner to bid 6NT if maximum, and to pass 4NT if minimum.
2NT opening by partner is not forcing. You can pass with fewer than 5 points, because you know game is unlikely. (20 + 4 is not enough)
But, a 2♣ bid is forcing. Unless responder holds a good five+ card suit with at least an ace and a king (a "positive"), they make a waiting response of 2♦. This leaves room for opener to describe their hand. Positive bids (2♥, 2♠, 3♣ or 3♦) promise five+ card suits with two of the top three honours. 2NT or 3NT shows 8-10, or 11+ points, without a five-card suit. It's better to bid 2♦ on any hand without a clear suit, because 2♣ p 3NT (to show 11+ points) has wasted a lot of your own bidding space. Better to conserve it to find out what the strong hand holds. After responder has described their hand, opener will bid no trumps to describe their exact number of points and to show the balanced shape.
Summary: 2NT openings with balanced responding hands.
2NT p p p (Responder has fewer than five points).
2NT p 3NT (Responder has enough for game opposite 20,21)
2NT p 4NT (Responder is inviting 6NT if opener is maximum).
2NT p 6NT (Responder has enough for slam opposite 20.21, i.e. 13+)
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