When your partner opens in a major suit, playing "2 over 1 forcing game", it is essential to the system that you respond 1NT for one round force.
Opener Responder or Opener Responder
1
1NT <= forcing
1
1NT <= forcingand the range of 1NT change from 6-9 to 5-11 hcp (high cards points)
However, many partnerships adopt an inverted response bidding for 1
and 1NT, after partner has opened 1, because this makes an improvement in the
bidding. Without the inverted response, minimum hands (12-15 hcp) in 4=5=2=2 distribution
like:KJxx 
Q9xxx
Ax 
Kx
or AQxx J87xx
Ax Qxhave no suitable bid after 1NT forcing because opener would have to bid 2 Clubs with 2 cards or rebid his 5 cards heart suit.
Examples of 1nt inverted and forcing are:
Opener Opponent Responder
1
pass
1 => is 1NT
forcing (5-11 hcp) up to 4 cards in Spades;1
pass
1NT => shows 5 or + cards in Spades and unlimited hcp.After 1
from responder, the opener of 1
Bids:a) 1NT to show 4 cards in Spades (hand type 4=5-x-x) and minimum. If responder has 4 cards in Spades he bids 2
with 5-9
hcp and 3 with 10-11 hcp.Example: Opener =>
KJxx Q9xxx
Ax Kx
Responder => A9xx 10x
Jxx QxxxOpener Responder
1
1
Response denies 5 cards in spades and can have zero up to 4 cards so must be
alerted (!)1NT 2
is a SIGN-OFF and must be alerted because it shows 4 cards in
spades.
b) a minor suit at level 2 to show his second suit (can be 3 cards in 5-3-3-2)
Opener Responder
1
1 Opener
without 4 cards in other suit and without 6 cards must bid 2
with 3 cards
2minor in Clubs (a) or 2
with 3 cards in diamonds (b) (in case of 2 cards of Clubs)Examples: (a)
A9 KJ10xx
Qxx Kxx
or (b) Kxx K9xxx
AJx Kxc) 2
with 6 or more cards 12-15 hcp and
may or may not have unremarkable spades holding (with
8xxx
AKJ1087 Ax
x better to say 2 than 1NT after
1 from partner).Opener Responder
1
12
<= shows 6 (or 7) cards in hd) 2
to show strong hand 18-20
HCP (hand type 4=5-x-x). If partner then bids a minor suit, with singleton we
can pass, but with 3 cards we can go to game in his suit by either making an invitation or
bidding directly 5 in his suit depending on our first controls (Aces) in majors.Opener Responder Opener Responder
1
1
1
12
<= shows 18-20 hcp
2
3 <= shows 6 or 7 cards sign-off 5-7 hcp4=5-x-x ?
Opener with
AQxx KQJxx
AQx x
must passOpener with
KQxx AKJxx
Kx Kx
must passOpener with
KQxx AKJxx
x AJx
bid 4Opener with
AKxx AK9xx
x Axx
bid 5 e) 2NT to show strong hand 18-20 HCP, necessarily with 4 cards in other suit (hand type 5-4-x-x). This bid will distinguish a 5-5 distribution from a 5-4 distribution.
So after 2NT, the responder bids 3
asking
for explanation of the suit.If the Opener has opened 1
and he doesn't
have 4 cards in spades, he bids:3NT => having 4 cards in Clubs with 5-4-2-2;
3
=> having 4 cards in Clubs with
5-4-3-1;3
=> having 4 cards in Diamonds with
5-4-2-2;3
=> having 4 cards in Diamond with
5-4-3-1;4
=> having 7 cards in Hearts, closed suit,
with 18-20 hcpIf the Opener have open 1
then he bids:3NT => having 4 cards in Clubs with 5-4-2-2;
3
=> having 4 cards in Clubs with
5-4-3-1;3
=> having 4 cards in Hearts with
5-4-x-x;3
=> having 4 cards in Diamonds with
5-4-x-x;4
=> having 7 cards in Spades, closed suit,
with 18-20 hcpIf responder bids a different suit, without asking 3
,
this is sign-off, so if he bids your singleton or doubleton you should pass, but
if was your tripleton (or 4 cards in a tricolor hand) you can think in game and
depending on your first controls in the majors and honor in support of your partner,
you make a invitation or directly bid game or maybe a small slam!f) Jump in another suit is 5-5-x-x with 18-20 hcp. The exception occurs in the rarely hands like 6-5-x-x where the 15-17 hcp are all concentrated in the 2 suits making strong suits with 4, 3 or 2 losers, because you cannot open in 2
having only 16-17 hcp even with 2 presumable losers!Experience shows us numerous disasters when the opener of 2 Clubs having two long suits must make his second declaration at level 5 and his partner passes in his singleton having 4 cards in the other unbidded suit => 2
4 pass passWhat do you bid with
x AKQ10x
AKJ9xx x,
4NT or 5 or 5
or double? Do you make an agreement with your partner about that? And if your partner
doubles 4 to show blank hand or 10xxx in
Spades expecting to find you with 4 or 5 sure tricks, what will that outcome be?g) Jump in the same suit (denying closed suit) is always a problem because some partnerships prefer to use the jump just in invitation cases, with 6 cards and 16-17 hcp (used more), and others use it in game forcing to show 18-20 hcp. Both ask for 2 cards support from partner, but the first case (invitation) needs also 8 hcp or more to continue. In both cases another suit from responder shows weak hand with 6 or 7 cards, so with singleton the Opener can pass even with maximum hand.
Note: It is important to assume that always another suit from responder is not forcing but just a invitation only in his suit (in misfit hand drop the bidding as soon as possible – Terence Reese).
h) Jump in 3NT shows 18-20 hcp in hand type 5-3-3-2, but if the partnership use the jump rebid to show invitation with 16-17 hcp with 6 cards (used more) with 18-20 hcp and 6 solids cards in your suit you can also bid 3NT.
i) Jump to game in major suit tends to show 18-20 hcp with 6 or 7 cards in solid suit.
In the opener's second bid, after responder bids 1NT showing long suit in Spades (unless 5 cards), the opener bids:
j) 2
with 3 (or 4) cards in
Spades and minimum hand 12-15(bad) hcpk) 3
with 3 (or 4) cards in
Spades and invitation hand 15(good)-17 hcpl) 4
with 3 (or 4) cards in
Spades and strong hand with 18-20 HCP (4-5-2-2 or 3-5-3(2)-2(3)m) 4 in a minor suit at level 4 (splinter) showing a singleton with 4 cards in Spades in strong hand 18-20 hcp 4=5=3(1)=1(3) or 4=6=2(1)=1(2)
n) jump to a minor suit, forcing game, in principle 5-5-x-x, and then bidding 4
to show 3=5=4(1)=1(4) or 3=5=5(0)=0(5) in a hand of 18-20 hcp. The singleton or
void is marked by exclusion.In hands with 16-17 hcp, opener after 1NT must bid like having 12-15 hcp in first round and bid again if he has chance:
A 1NT response after 1
opening or 1 response after 1
opening shows 5-11 hcp and can be done with many types of hand, so the Opener must
be careful in his second bid and prudent assuming partner with minimum
range hand 5-7 hcp in principle. So he needs to bid like having 12-15 hcp and not
16-17 hcp, because a jump is reserved for a strong hand with 18-20 hcp.Partner could have a middle range hcp (8-9) or a maximum range hcp (10-11) hand.
If your partner has a maximum range (10-11 hcp) after your bid, he must bid again, normally NT or jumping to his long suit or jump to your suit to show 3 cards support or making a simple raise in your other suit. In all these cases you can go to game without problem.