Source: Improve Your Bidding Judgment By Neil Kimelman
Like the Law of Total Tricks, this subject has generated a great deal of literature. Eddie Kantar is one notable world-class player and teacher who has written extensively about forcing auctions. Simply stated, when your side has game-going strength, a pass by either partner in a competitive auction is forcing. This allows you more options with which to describe your offensive and defensive potential. Here is a list of possible actions in a forcing pass auction example, with you and partner being North-South:
1. Game-forcing.
Since 2
was game-forcing, the forcing pass principle applies. The meanings of various actions by North now are as follows: Pass—no strong opinion, often showing either short hearts (zero or one) or long hearts (three-plus). It is a green light, if South is interested in bidding on. However, if South then doubles, any further bid by North shows a serious slam try. New suit—this bid is natural, usually indicating shortness in the opponents’ suit, and looking for help with the decision as to what to do if the opponents bid 5
. It denies a serious slam try, because with that hand North would pass and then bid his second suit.
Four spades—this bid says I want to play 4
‘, and inferentially denies a slam try or strong distributional hand. Double—this shows either minimum values and/or no fit in clubs, and/or a doubleton in their suit, which is the worst holding possible. This is a strong yellow light to partner.
This is a hand from the 1978 Vanderbilt.
Both tables arrived at this point in the bidding.
Passell’s sequence had shown a strong hand, good enough to bid game in spades by himself. The opponents, by their bidding, were almost certainly sacrificing. The forcing pass structure allows East, in this example, to conunu-nicate to his partner what he thinks the partnership should do, with the knowledge that he has at the time. In this case, Rosencrantz did not have a fit for spades and had length and some strength in the two suits bid by South, so should clearly have doubled. At the table he passed, which normally would say, ‘Partner I don’t have any strong opinion what to do—you decide: Passell reasonably bid five spades on that assumption, and was very disap-pointed with dummy. The opponents gave a trick away, but 5 still went down one, while 5 would have been down at least three, doubled!
Here is an interesting hand that exemplifies an important high-level strategy, especially at teams. It came up in the 2005 CNTC finals.
You hold as South: 
A twenty-count. The bidding goes, with East-West vulnerable:
All of a sudden this hand has taken a downturn. Not only have the opponents not let us play in 4 but also I am not sure we can beat 4. Since they are vulnerable I decided to take insurance, along the lines of Tip 11, and bid one more. However, I bid 5
, not 5. This bid tells partner that I have a longer diamond suit, and in case his hearts are poor or we have a better diamond fit, 5 will be safer. Was I ever right!
This was the full deal:
As you can see 5 is down one and 5 is down many, while 4 may or may not make. However, if you exchange West’s 3 for the 3, 4 makes easily.
One point to note is that since North had to bid on the first round, his pass of 4 is not forcing, but only says, ‘I have nothing to say’. It suggests a bad hand, which describes North’s holding nicely. Here is another one: 
Being too strong for 1NT. you open 1 and partner bids 1. Looks easy… but what do you do? At the table, South bid 4. Partner with 
trotted out Blackwood and got you to a bad slam. Is there a problem? If so, what is it?
I believe that the 4 bid is wrong for a couple of reasons. First, your hand is not good enough. Besides having only 18 HCP you have no distribution. How does partner know whether you are balanced or semi-balanced?
An alternative that most experts would choose is a bid of 2NT, showing 18-19 HCP and a balanced hand. Over the likely 3NT by partner, you can pull to 4, confident that partner will have a good idea as to both your strength and distribution. Another advantage of bidding 2NT with this type of hand is that when you bid 3 directly partner can infer that your hand is either unbalanced or semi-balanced, such as 24-2-5 shape.
Okay, now try this one. You are South.
The bidding goes:
This should be easy. Bid 6. Partner has enough values to commit to game when all you showed was a minimum response, no fit for partner, and at least six diamonds. You might hold:
Also, partner has implied he is short in hearts by bidding spades and clubs, then strongly supporting diamonds.
I was shocked when the author of the article in which this hand was described suggested that North was at fault for not getting to the slam! My view is almost the exact opposite. By making a value call of 5. North paved the way to easily getting to six. However, South did not take into account the difference between what he promised and what he actually had, thus what partner needed. As an aside. most experts would rebid 3, not 2 over 1. Sometimes you know what you want to do, but need strategy to accomplish that goal. This spectacular result is from way back. It occurred at the 1976 Nationals in Salt Lake City, which happened to be my first big tournament. Your hand as South is: 
Playing matchpoints, vulnerable against not, the bidding goes:
What do you bid? First, we need to examine the previous bidding. It looks like partner has both black aces and a second-round heart control. What else can he have? The A and the A? With those cards, partner might have bid 5 on the way to 6. Also, it is likely that one of your heart-bidding opponents has the A.
What will happen If you bid what you think you can make 7? The opponents at this vulnerability will likely take the sacrifice. Is there anything you can do about this?
Mike Smolen passed! His reasoning was the opponents would be likely to sacrifice in 6 over 6, but then might not sacrifice against seven ‘knowing that the opponents were ‘pushed’ to the grand slam. Smolen got what he wished for. West sacrificed in 6 and Smolen duly pulled his partner’s double to 7. The opponents let the logic of the auction dictate that 7 had a good chance to go down, since it hadn’t been bid on the previous round. This created a well-earned swing as Smolen’s teammates sacrificed in 7 after a different auction. The full deal: 
Here is a final high-level competitive decision for this chapter. You, East, hold at favorable vulnerability:
Let’s look at what you bid with this hand in various auctions.
A bid of 4 seems reasonable. It would be nice to bid4, but you really don’t have the values for that bid.
In this situation, 5 is comfortable. You are suggesting an offensively oriented hand with spade shortness.
The air is getting more rarefied. How do you feel now about bidding on? At the 2004 CNTC finals, some Fasts bid 6. This became the final contract, sometimes doubled, but at this level neither side could make anything. The full deal: 
The secret on hands like this is not to let the opponents push you into actions that are not supported by your cards.