If you play weak NT 12-14 HCP, open this hand 1NT.
If you have
a ♥ fit, you may be pre-empt by opposing spades when opening 1♥. If you have no fit, your partner will take a good decison if you open 1NT.
Remark : when responding to 1NT with weak 5♠-4+♥ (maxi 10 HCP) it would be good to have developments to bid these hands. If not, you risk playing a 5-2 fit in spades with a 4-5 or
5-5 fit in hearts.
If you play strong NT 15-17 HCP, open 1♠.
A spade fit occurs half the time, and it's better to play in spades especially a
part-score.
And in that case you have advantage to be in the higher ranking suit.
If you have no spade fit, opponents are not well-placed to overcall with success, on either 1♠ or 1NT opening.
But beware, after opening 1♠ you will have a difficult rebid in the French standard.
If partner responds 1NT, you will
struggle to bid this hand. You'll say it was better to open 1NT.
If partner responds
2♠, it is very dangerous to
make a game try. You'll say that it was preferable to open 1NT (but you shoul have missed the spade fit, which statistically happens half the
time).
The solutions in MAJEURE SECURISEE :
the 2♣ SAUVET in response to opening : 9+ DH 3 cards support, associated with the 2 level raise = 6-8 DH.
the 2♣ GAZZILLI rebid by the opener : forcing, at least 14+ HCP, which contains balanced hands of 15-19 HCP.
Conclusion : open possibly 1NT with 5 hearts (for its barrier effect) but banish opening 1NT with 5 spades (that is detestable to miss fit in the highest ranking
suit.
1NT = 15-17 HCP
What to do with 5♠-4+♥ (max 7 HCP) in response to 1NT opening.
Play the STAYMAN 3 responses. Opener's
rebid of 2♥
shows 4-5♥ and may have 4-4
major.
If opener rebids 2♥ or 2♠, you pass or possibly upgrade the 9th fit to propose the game.
If opener responds 2♦ , rebid 2♥ TRANSFER for spades. On the rectification you pass with the weak hand and you calmly describe your hand by
bidding 2NT or 3x with an invitational hand. And bid of 3NT shows a major 5-5 without ambitions, while 4m shows ambitions.
Of course the direct 2♥ TRANSFER is now weak or game force, except with invitational hand of 6+ ♠ .