Source: www.bridgeguys.com This conventional method carries the designation of the surname of Mr. Michael Cappelletti, born in the year 1942, of Alexandria, Virginia, United States, who developed this conventional method as a defense method against an opening of No Trump by the opposing side. There is the matter that other bridge authors and experts have devised the same conventional method and is also known under their surnames.
Cappelletti Michael
Cappelletti Michael
Note: An interview of Mr. Michael Cappelletti was published in the Daily Bulletin, Tuesday, March 13, 2007, Volume 50, Number 5, of the 50th Spring North American Bridge Championships held in St. Louis, Missouri United States. The essence of the interview were his personal views on the concept behind this conventional method.

Added to this confusion is also the designation Pottage for the same concept, ascribed to Mr. John F. Pottage of London, England, under which designation the conventional method is known. The origin of this concept is also claimed by Mr. Gerald W. Helms of Charlotte, North Carolina, United States, but is not designated as such.

Therefore, when a bridge player refers to Cappelletti, Hamilton, or Pottage, then the bridge player refers to the identical defense method employed against an opening of No Trump by the opponents.

The concept is employed as a defense method following an opening of No Trump by the opponents in either the direct seat or in the balancing seat. The overcall promises either a one-suited holding or a two-suited holding with values not exceeding 15 points. Importance must be given to the state of vulnerability and the location of the values, which should be in the suit or suits promised or indicated.

Although it is a matter of partnership agreement, the one-suited holding should contain at least a 6-card plus suit, and for a two-suited holding the distribution should be at least 5-5. Some advocates have reduced the distribution to 5-4 if the values are located only in the two suits such as: KQJ10 and AQ1087. Some very aggressive players will even decide to overcall with a 4-4 distribution, but only in the Major suits. This is purely a matter of partnership understanding.

After a No Trump opening, the bids of the overcaller (also referred to as the intervenor – partner is called the advancer) are as follows:

Opponent Intervenor Meaning
1NT The range of the No Trump should be announced.
2club suit Shows any one-suited holding.
2diamond suit Shows Hearts and Spades, both Major suits.
2heart suit  Shows Hearts and an unspecified Minor suit.
2spade suit Shows Spades and an unspecified Minor suit.
2NT Shows both Minor suits.
Double If the intervenor has not previously passed, then any double is for penalty. Partner must pass.

Each overcall generally promises fewer than 15 high card points. All overcalls at the three level are natural.

Advancer and Continuances

The advancer has several options, not forgetting that the 1NT bidder generally sits to his left with a defined strength and distribution.

Responses after Intervenor has overcalled with 2club suit showing a one-suited holding:

Pass: with at least 6-card support in Clubs.
2 diamond suit: Relay bid, allowing his partner to pass or bid his suit. If the suit is Diamonds, then the intervenor passes. However, if the intervenor holds a 6-card Club suit and a 4-card Diamond suit, then the intervenor rebids 2 No Trump. An example would be:
Intervenor
spade suit 64
heart suit 10
diamond suit KQ97
club suit AQJ853
2NT
2heart suit: This bid shows a 5-card Heart suit and also weak values.
2spade suit: This bid shows a 5-card Spade suit and also weak values.
2 NT: Promises 11 plus High Card Points and support for all four suits. Partner is invited to bid game with a maximum.

Responses after Intervenor has overcalled with 2diamond suit showing both Major suits:

Pass: with at least 6-card support in Diamonds.
2heart suit: Cheapest Relay bid, choice of suit, unconstructive. Shows preference.
2spade suit: Choice of suit, unconstructive. Shows preference.
2NT: Shows length in both Minor suits and is an asking bid for the better Minor suit of the intervenor.
3club suit: This bid shows a 6-card length in Clubs
3heart suit: Invitational, promising 4 or more Trump. This jump may also be regarded as preemptive in nature. Partnership agreement.
3spade suit: Invitational, promising 4 or more Trump. This jump may also be regarded as preemptive in nature. Partnership agreement.
Responses after Intervenor has overcalled with 2heart suit or 2spade suit showing the bid Major suit and an unspecified Minor suit:
Pass: Shows a fit for the known Major suit and between 0-7 points.
Single Raise: Shows a fit for the known Major suit and about 8-9 points.
2 NT: This is a relay bid by the advancer asking the intervenor to bid his unspecified Minor suit. However, if the advancer raises the Major suit of the intervenor on the second round of bidding, then the advancer shows a good fit for the known Major suit and around 10-12 points. This is then invitational.
Responses after Intervenor has overcalled with 2 No Trump showing both Minor suits:
3club suit: Shows a weak holding. This is a preference for Clubs and also a sign off. No game interest.
3diamond suit: Shows a weak holding. This is a preference for Diamonds and also a sign off. No game interest.
3heart suit: Advancer promises a one-suited holding in Hearts (generally a 6-card plus suit) and shortness in both Minor suits.
3spade suit: Advancer promises a one-suited holding in Spades (generally a 6-card plus suit) and shortness in both Minor suits.
4club suit: A jump in Clubs promises a distributional holding, good support, and invites game if the intervenor has maximum values.
4diamond suit: A jump in Diamonds promises a distributional holding, good support, and invites game if the intervenor has maximum values.
If the intervenor has previously passed, then a double by the intervenor cannot be for penalty. In this case the double promises either a one-suited holding in Clubs or a two-suited holding in the red suits, Diamonds and Hearts. The advancer relays with a bid a 2 Clubs, which the intervenor passes if Clubs is the suit.
1. If the intervenor has a two-suited holding in Diamonds and Hearts, then the intervenor bids 2 Diamonds after the 2 Clubs relay. The 2 Diamonds rebid promises good support in both red suits. The advancer must then determine whether the contract should be in Diamonds or Hearts. With better Diamonds the advancer should pass since game in a Minor suit is not an option opposite a 1 No Trump opening by the opponents. With better Hearts the advancer will correct to Hearts and the intervenor will most likely pass since the intervenor has previously passed.
2. If the intervenor rebids 2 Hearts after the 2 Clubs relay, then the intervenor promises Hearts and Clubs as a two-suited holding, whereby the Heart suit is generally the stronger, normally longer suit. The advancer either passes or corrects to Clubs since the Minor suit is always the Club suit. 
3. If the intervenor rebids 2 Spades after the 2 Clubs relay, then the intervenor promises Spades and Clubs as a two-suited holding, whereby the Spade suit is generally the stronger, normally longer suit. The advancer either passes or corrects to Clubs since the Minor suit is always the Club suit. 
Note: Regarding the inclusion of the pre-condition that a rebid by the intervenor of either Major suit shows that suit and only the Club suit as the second suit is from the original version as set forth by Mr. Michael Cappelletti. However, this pre-condition has been revised over time, even by the developer himself, and the consensus is that the rebid of the intervenor of a Major suit shows that suit and either of the Minor suits. Note: The general consensus is also that the advancer, once the intervenor has defined the two-suited holding, passes with values ranging from zero to about 6/7 high card points. If the established fit is a Minor suit, then the advancer will not seek game or even raise partner opposite a No Trump opening by the opponents. However, if the partnership has established a Major suit fit, then the advancer may raise generally with a good 8 to 11 points. These conditions are, as always, a matter of partnership agreement. Note: Both the intervenor and the advancer must agree as to the length and strength of the one-suited holding and/or the two-suited holding generally in relation to the state of vulnerability. The decision to compete in this manner should depend on the responder of the No Trump bidder remaining silent, and be based on a relatively sound valuation method and/or trick-taking ability of the holding(s).

In the case that the auction proceeds as follows: 1 No Trump – 2 Clubs – Double, a Redouble shows 7 or more high card points and support in all suits, and invites his partner to compete on the three level.

As already mentioned, the Cappelletti conventional method can be used as either a direct overcall or in the pass-out seat. The conventional method can also be used after the opponents have opened a 2NT or even a 3NT. The conventional method can also be used over Gambling 3NT. The conventional method can also be used if your partner has opened the auction and an opponent overcalls with 1NT.

As with all conventional methods there are some flaws to the concept. For example if the intervenor doubles and the advancer holds a long suit, he may not preempt to show this suit. The advancer is first obligated to bid 2 Clubs and later indicate the long suit and shortage in all other suits.

When this auction happens, the intervenor must base his rebids logically upon the insistence of the advancer for this one long suit. Since the advancer is not bidding according to the guidelines set forth in the established responses, then the intervenor must infer that advancer has a preemptive-style suit, which he has been unable to bid.

Mr. Jerry Helms arrived at a solution to solve this problem in the bidding sequences with the decision to reverse the meaning of an immediate bid of a Major suit and the meaning of the artificial 2 Clubs, as shown below:

2club suit: An artificial bid showing a two-suiter and one unspecified Minor suit. The advancer bids 2diamond suit asking for the Major suit. If the advancer does not have support for the suit of the intervenor but good support for either Minor suit, the advancer rebids 2 No Trump.
2heart suit: This bid is natural and shows at least a 6-card plus Heart suit.
2spade suit: This bid is natural and shows at least a 6-card plus Spade suit.