Conventions in depth
Over a 1♥ or 1♠ opening, a new suit at the two level by an unpassed responder is forcing to game.
The bid is natural (for example 1♠ – 2♣, 2♦ or 2♥), and responder needs an opening hand (about 13+). The qualifying bids are the new suits that rank below opener’s and so sit at the two level without jumping; a jump, such as 1♥ – 2♠, is something else entirely, not a 2/1.
Because game is guaranteed, no bid is needed only to keep the auction open. That frees every call below game to describe shape and strength (extra length, a side suit, a control), which sharpens both the choice of game and the decision on slam.
Hands not worth a two-level start respond a semi-forcing 1NT instead (about 6–11 or a bad 12). Opener bids again with any unbalanced or stronger hand. With a completely flat minimum opener may pass and play 1NT: five cards in the major, three-three-two outside (or four spades alongside five hearts), and no more than 12 points. Between them, the game-forcing 2/1 and the semi-forcing 1NT catch every strength of responding hand without losing the low-level room.
Now and then the slow auction shows slam values but never pins down a single agreed eight-card fit: two useful five-card suits, say, with neither raised. With about 30 combined points, at least three aces and a sound control count, the hand in charge jumps to 5NT, a pick-a-slam ask. Partner names the best spot: six of whichever suit is the longest real fit between the hands, or 6NT. A suit slam plays well on even a seven-card fit, so the ask reaches that rather than a doubtful 6NT. Holding three aces yourself keeps the small slam safe even if partner has none.
Two things switch the game force off. After an overcall, a 2/1 is only a one-round force, so opener may pass. And when responder has already passed, with partner opening in third or fourth seat, that hand cannot hold opening values, so nothing it bids can promise game.
A passed responder bids Drury or raises with a fit. Without one it bids 1NT, not forcing, on about 6–12 points, and opener may pass it with a balanced minimum.
2/1 is BidMaestro’s recommended baseline, but it is a switchable convention: turn it off and a two level bid over a one level opening becomes a one-round force in the original Standard American style.
