After opening 1 in a Major, the opener's rebid

Responder's supporting bid at the 2 level, means that he has 6-10HCP and at least 3 cards in the suit. Opener has several possibilities:
With a 1st zone hand (12-14HCP)the side isn't strong enough to go for Game. He can PASS or repeat the major at the 3 level to avoid a possible overcall.
With a 2nd zone hand Opener bids :

2 SA; a general trial bid looking for game or even Slam (forcing for a round.)
3 in another suit; a trial bid looking for the best game with an unbalanced hand (forcing for a round.)

With a 3rd zone hand 4 in the major suit imposing Game if a Slam isn't possible.

S	W	N	E

Problem E5173 4 spades Slam is out as you don't have a singleton and your Partner has less than 10HCP. On the other hand even if the support was minimum, Game is possible.

S	W	N	E

Problem E1691 PassGame isn't possible with this flat hand

Trial bids are used to propose game and, sometimes, slam. They require a 2nd zone hand (15-17HCP):

2NT : a general trial bid
3 in a minor with an unbalanced hand (you need a void or a singleton) and at least 4 cards in the suit. This tells Responder that you wish to go to Game but need an honor or two in this suit in the hand opposite.
the other major with 4 solid cards. It's possible that Responder has a weak hand with 6HCP and 4 or 5 cards in the other major. This rebid allows you to find a possible better fit in the other major

S	W	N	E

Problem E1695 With a 2nd zone hand, propose Game and check at the same time that Responder doesn't have a 4 spade fit.

S	W	N	E

Problem E5176 Your partner knows that your problem is with this suit in particular. Thanks to this trial bid, he can get over it either by ruffing clubs or with some extra club honors.

Be careful!

Opener's rebid of 3 in the major after a supporting bid, is a pre-empt to avoid overcalls and not game proposal.
Slam bidding generally begins with a 2NT general trial bid (and not with a rebid in a 2nd suit)
After Responder's support, the notion of a maximum 2suiter bid no longer exists.
Don't use the trial bid of 3 in a minor without a void or a singleton.

S	W	N	E

Problem E1696 Extending the pre-empt ... to avoid nasty overcalls. Responder has to pass even if his bid was maximum!

Subsequent bidding
After Opener's 2NT rebid :

Minimum, Responder returns to Opener's major at the 3 level.
Maximum, he bids Game : 4 hearts or 4 spades.

After Opener's rebid of 3 in a minor:

Without any honors in that suit, Responder returns to Opener's major at the 3 level.

After Opener's rebid in the other major:

With maximum support, Responder bids Game in the best major
With minimum support, he stays at the 3 level in his best major

S	W	N	E

Problem E1704 Responder who was maximum with 9HCP bids Game.

Main

Detail specifications 12AB - Level 2 ★

After opening 1 in a Major, the opener's rebid

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