When it is your turn (in the first round of the auction) to open the bidding you will normally Pass with less than 13 pts. This Pass immediately puts an upper limit (of 12 pts) on the strength of your hand, and converts all future responses you make to your Partner's Opening bid into limit bids. This means that the Opener can Pass at any time, even after you bid a new suit.
It is therefore important to make an aggressive bid if you hold 11-12 pts (a so-called maximum pass).

The various responses by a Passed hand (Bidding Guide p.16) are listed on the Diagram below.

• Responses with minimum hands (6-10 pts) are the same as if you had not passed previously.

• However Responses with maximum pass hands (11-12 pts) are distinctly different.
  1. Jump raise Opener's major suit if you have trump support
  2. jump-shift showing a 5 card (or longer) suit
  3. Bid 2NT with no 5 card suit (or bid a 4 card suit at the 1 level)

• If you have a trumpfit with Partner's suit and, counting shortage point, now have 13+ points : bid straight to Game.

Responses to a 1NT opening bid are the same as if you had not passed before (Bidding Guide page 3), but they have of course an upper limit of 12 points.
Here follow some typical examples.

1. If your Partner opens with 1♣ or 1♦   Your Response = 1NT
   With a balanced hand and no 4-card major suit bid NT

2. If your Partner opens with 1♥ (or 1♠)   Your Response = 2♥ (or 2♠)
   Single raise your Partner's major suit.

1. If your Partner opens with 1♣ or 1♦ or 1♥  Your Response = 1♠
   With 6+ points and a 4-card major suit : bid new suit at the 1 level

2. If your Partner opens with 1♠   Your Response = 2♠
   With 6-10 points and trump support single raise Partner's major suit.

1. If your Partner opens with 1♣ or 1♦   Your Response = 2NT
   With a balanced hand, 11-12 points and no 4-card major suit jump bid NT

2. If your Partner opens with 1♥ (or 1♠)   Your Response = 3♥ (or 3♠)
   With 11-12 points and trump support jump raise your Partner's major suit.

1. If your Partner opens with 1♣ or 1♦   Your Response = 2♠
   With 11-12 pts and a 5 card suit : jump-shift

2. If your Partner opens with 1♥ (or 1♠)   Your Response = 3♥ (or 3♠)
   With 11-12 points and trump support jump raise Partner's major suit.

1. If your Partner opens with 1♣ or 1♦   Your Response = 2♠
   With 11-12 pts and a 5 card suit : jump-shift

2. If your Partner opens with 1♥ (or 1♠)   Your Response = 4♥ (or 4♠)
   You now have 13 points (including shortage pts) and a trump support : make sure you reach a Game contract (Partner may Pass at any time) and Game raise Partner's major suit.

1. If your Partner opens with 1♣ or 1♦   Your Response = 1♥
   With 11-12 pts and a 4 card suit : bid that suit at the 1 level

2. If your Partner opens with 1♥   Your Response = Jump raise to 3♥
   Showing trump support and a maximum pass (now 11 HCP + 1 SP = 12 points).

3. If your Partner opens with 1♠   Your Response = 2NT
   Showing a maximum pass but with no 5+ card suit.

Normally, after your opening bid, Partner's response of a jump raise, jump shift or 2NT bid are forcing to game.

But when he has passed already Partner's responses of a jump raise, a jump shift or bid of 2NT show 11-12 points and are invitational only ! You should pass with a minimum (12-13 points) but should raise to Game with anything more.

After a new suit bid by Partner you also may pass at any time if you feel a Game contract is out of reach. Be aware however that if you find a trump fit and Partner has an unbalanced hand his strength may increase (through additional shortage points) to 13 points or more.

Here follow two examples.

Hand 7
Partner has passed when it was his turn to open the bidding.
You have a balanced hand with 15 points, and open (in 3rd position) with 1♣.

1. If your Partner responds with 1♦, 1♥ or 1♠   Your reply = 1NT
   With a balanced hand and no 4-card major suit bid NT

2. If your Partner responds with 1NT   Your reply = Pass
   Your Partner has 6-10 points, not enough for Game.

3. If your Partner responds with 2NT   Your reply = 3NT
   Your Partner has 11-12 points, enough for a Game contract.

4. If your Partner responds with a jump shift of 2♥ (or 2♠)   Your reply = 4♥ (or 4♠)
   You have a 5-3 trump fit and enough points for a Game contract.

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(Down - Up - Top)
Hand 8
Partner has passed when it was his turn to open the bidding.
You have a balanced hand with 12½ points, and open (in 3rd position) with 1♣.

1. If your Partner responds with 1♦ or 1♥   Your reply = 1♠
   Always bid your major 4-card suit.

2. If your Partner responds with 1♠   Your reply = 2♠
   Your Partner has 6-12 points. Your hand has increased to 13 points. If Partner is maximum and unbalanced a Game contract can not be ruled out entirely.

3. If your Partner responds with 1NT   Your reply = Pass
   Your Partner has 6-10 points only, 7 tricks is probably all you are going to make.

4. If your Partner responds with 2NT   Your reply = Pass
   Your Partner has 11-12 points and you only 12½, not enough for Game.

5. If your Partner responds with a jump shift of 2♥   Your reply = Pass
   You have only 5-2 in the trump suit, but further bidding may get you in hot water.

6. If your Partner responds with a jump shift of 2♠   Your reply = 3♠
   You have a 5-4 trump fit, even with 25 points in the combined hands there is a chance for Game.