Kaitlyn S, on 2016-September-03, 20:09, said:
Think of it this way. The reason 2NT shows 11-12ish when partner could be minimum is that two minimum hands want to try to stay below 2NT (unless they have a fit and the opponents push them.) Note that 2NT isn't forcing.
Over the reverse, 2NT isn't forcing either. What does your partner have? You don't need very much to have enough for game. If you bid 2NT non-forcing, you are saying you don't have enough to make game opposite a minimum reverse.
The vast majority of good players play 2nt as forcing, looking for signoff in one of opener's suits.
It's split into two main camps:
1. Bridge World Standard style -- cheapest call of 4th suit (at 2 level) or 2nt is forcing, but normally weak. Opener usually rebids 1st suit with non-GF reverse. If 2-level 4th suit was available, 4th suit = weak, only 4 cds in major response, 2nt = natural forcing. After the weakness signal, can pass opener's minimum rebids. So on this style, on your first example conceivably the auction would often continue 1c-1h-2d-2s!-2nt which you could pass, or 3c if opener had 6c and you could comfortably pass that.
2. Lebensohl/Ingberman style -- 2nt is always the potential weakness signal.
There are also some split if after 1m-1M-2R-2M whether responder's rebid of major is forcing or not, most play as forcing 5+M.
And after weakness 2nt, there is also some split between always rebid 3c even if opener's first suit is diamonds (to cater to responder weak long clubs 4M), vs. reserving 4th suit for say GF hand looking for stopper 4th suit. Arguably one could play 1d-1s-2h-3c as the weak 4-6 long club hand NF if playing everything else forcing.
Why people play 2nt as F1:
- It allow distinguish between show fit for partner with good hand, forcing (9/10+), vs. weaker hand trying to play partial. If the direct preference wasn't forcing, showing the fit after 4th suit would often entail bypassing 3nt which can be problematic.
- 2nt nf is aiming for a very narrow target where only 2nt makes exactly 2 but 3 of opener's minor goes down. Opener will often have 6 cd opening suit, and even if 5-2 sometimes the suit contract plays better. It just doesn't come up often enough where 2nt is last and only making contract to give up the other advantages of having lots of forcing calls available.
- Now you don't have to jump 3nt with wide range, easier to bid after 1c-1s-2h-3nt if 3nt has reasonably narrow range, and can do something like 3nt=12-14, 2nt then 3nt =8-11, and with 15+ you can bid 2nt to start without any fit for partner's suits then 4nt/6nt/more/other as appropriate.