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Introduction to MOSSO: MOsca with Standard Spade Openings
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It's now more than three years since I bought a copy of "Fantunes Revealed" and became interested in that bidding system.  It soon became clear to me that Fantunes could be effectively simplified and I started to develop the SWIFT system.  More recently I've made some major changes to SWIFT and derived the MOSSO bidding system.  See my previous article (and the links therein) for the background to MOSSO.

Just as in SWIFT (and Fantunes), the MOSSO opening bids of 1, 1 and 1 are unlimited and forcing for one round, while the 2 and 2 and 2 openings are Intermediate, showing a 5+ card suit with 9-12 points.

The main difference is that a 2 opening is a standard Weak Two (5-9 points), while 1 is limited to about 10-16 points (and therefore non-forcing).  Stronger hands with 5+ spades are opened 1, which now becomes a 3-way bid: either clubs (13+), spades (17+) or balanced (any strength outside the ranges of 1NT or 2NT).

This is in some ways similar to a 1 opening in standard Polish Club, but there is an important difference: an unbalanced MOSSO 1 opening is only strong when opener has length in a black suit.  With 13+ points and length in a red suit the opening bid is still 1 or 1, regardless of the strength of the hand.  A MOSSO 1 opening is therefore less likely to be affected by high-level intervention than a Polish 1 opening.

The name MOSSO is an acronym: MOsca with Standard Spade Openings.

The purpose of this article is to present a summary of the MOSSO bidding system. I've left out much of the detail, but hopefully there's enough information for people to get started with the system.  I've also not covered developments after the 1, 1NT, 2 or 2NT openings because a partnership can retain their existing approach after these bids.

General nature of the MOSSO bidding system

It's a little difficult to classify the MOSSO bidding system as it is essentially an amalgam of parts of Fantunes, Polish Club and 2/1.  MOSSO brings together some of the best features of all three systems, while providing an effective interface between them.

One important feature of MOSSO is the 1 negative response to the 1 opening, which allows the partnership to stop at a low level when responder is very weak.  It also means that many sequences after a natural 1 or 1 response essentially reduce to 2/1 (or something similar), thus allowing a new MOSSO partnership to retain their existing methods.

The MOSSO opening bids of 2 of a suit aim to strike the right balance between obstructing the opponents and causing difficulties for the opening side.  Constructive bidding over a Fantunes 2 opening can be difficult, so reverting to a Weak 2 removes this aspect of the system.  It's much easier to develop the auction over an intermediate 2, 2 or 2 opening, which are still high enough to inconvenience the opponents.  These openings can still cause problems for the opening side, but reducing the range from 10-13 to 9-12 makes this slightly less likely.  The lower range means that MOSSO doesn't have to pass so many Weak Two hands (6-4 hands with 8 points also qualify) and this is partially offset by the ability to open 2 as well as 2 and 2.

There is still an issue with 11-12 point hands with 4-5 in the majors.  Although SWIFT opened these with 2, it has been decided that MOSSO should incorporate these into a 1 opening, in a similar way to Fantunes.  But the MOSSO 2 and 2 responses to 1 are game-forcing, since the use of the Kaplan Interchange supports a wide-ranging negative 1 response.

The need to open 1 with strong spade hands means that MOSSO can't really be categorized as a natural system, but it's usually fairly easy for opener to show this type of hand (even after intervention), after which most sequences have a natural basis.


Abbreviations used in this article:

NF non-forcing

F1R forcing for one round

GF forcing to game

OM other major


Opening bids in MOSSO

1    3-way bid: (a) 13+ unbalanced, either 5+ clubs or 4=4=1=4 shape;

                          (b) 17+ with 5+ spades;

                          (c) balanced with 12-14, 18-20 or 23+ points.  A balanced 12-14 points might                                have 5 hearts (but not 5 spades)

1          13+ unbalanced, either 5+ diamonds or 4-4-4-1 with 4 diamonds.  Might be 4-5 in                  the minors if 18+.

1          5+ card suit.  Normally 13+ points, but might be 11-12 with 4 spades (rule of 20).                     Denies 5-3-3-2 shape unless too strong for a 1NT opening.

1          5+ card suit, 10-16 points (or a poor 17).

1NT        15-17 balanced. The normal opening with 5-3-3-2 shape, although 1 is an                            alternative with 5 spades.

2, 2   9-12 points, either 6+ card suit or 5 cards with a second suit (normally 4 cards, but                 a 2 opening could have 5 clubs).  (May be 5-4-2-2)

2         9-12 points, either 6+ card suit or 5 hearts with a 4+ card minor.  (May be 5-4-2-2)

2NT       21-22 balanced - may have a 5 card major.

Higher bids       As in 2/1.


The 1, 1 and 1 openings are unlimited and forcing for one round.  They may not be shaded in 3rd or 4th position.

The point counts for unbalanced hands assume a 6 card suit or 5-4 in two suits.  The 1 opening, the club suit variant of a 1 opening and the normal range of a 1 opening therefore follow the rule of 22, or a queen more than 2/1.  Similarly, the 2, 2 and 2 openings follow the rule of 18-21.

2, 2 and 2 may be shaded third in hand.  For example, it's perfectly OK to open any sound Weak Two at the 2 level, even vulnerable.  The 2 level openings can be even lighter third in hand non-vulnerable.

4-4-4-1 hands with 12 points or less must be passed.  (It is accepted that 4-4-4-1 hands with 13 points don't strictly pass the rule of 22.)

An unbalanced 1 opening denies a 5 card major (unless 17+ with 5 spades), thus allowing opener to rebid in a 5 card major without implying a club suit.  

The 1 opening also denies reversing values with 5 clubs and 4 diamonds.  This makes it easier for opener's 2 rebid to be used conventionally.


Responses to 1

1           Any hand with 0-6 points.  Might also be stronger with no 4 card major if              unsuitable for a higher response, i.e. 7 points or 13+ balanced or 7-12 unbalanced.

1/1      7+ points, 4+ card suit.  May contain a longer minor with less than 13 points.

1NT        7-10 balanced (or a poor 11), no 4 card major.

2/2    13+, 5+ card suit, GF.

2/2    4-7, 6+ card suit.

2NT       Good 11-12 balanced, no 4 card major.

3         7-9 (or a poor 10), 6+ card suit, no 4 card major.

3         7-9, 7+ card suit, no 4 card major.


Rebids after 2 and higher responses are generally natural.

Opener's rebids after 1 - 1

1        2 way rebid, NF: (a) 12-14 balanced (3+ card suit, no more spades than hearts);

                                        (b) unbalanced with 4 hearts and 5+ clubs (or 4=4=1=4 shape).

1        3 way rebid, NF: (a) 12-14 balanced (3+ card suit, more spades than hearts);

                                        (b) unbalanced with 4 spades and 5+ clubs;

                                        (c) 17-19 (or a poor 20) with 5+ spades.   

1NT                18-20 balanced.  Responder bids as after a 1NT opening.

2                13-18 with 6+ clubs or 5 + 4.  

2                3 way rebid, F1R: (a) 20+ with 5 + 4;

                                                 (b) 20-22 with 5+ spades;

                                                 (c) 25+ balanced.

2                 20+, F1R with 4+ clubs and 4 hearts.  Over this 2NT is Lebensohl.

2                 5+ spades, GF.

2NT               23-24 balanced.  Subsequent bidding is as after a 2NT opening.

3                Natural, invitational.

3/3/3     Singleton or void in bid suit, 6+ clubs, GF.

3NT              Solid clubs with stoppers.

After 1-1-1/1, responder may raise, bid 1NT or bid 1 over 1 with 3-5 points. Other suit bids at the 2 level promise 7-12 points.   Responder jumps to 2NT (GF) with 13+ balanced.

 After 1-1-2 responder generally rebids 2, over which opener rebids 2NT with 25+ balanced.

Opener's rebids after 1 - 1/1

1 (over 1)   Any unbalanced hand with 4+ spades, F1R.

1NT                12-14 balanced.  Might have 4 spades over 1, or 5 hearts over 1.                                         Two-way Checkback applies over this rebid.

2                 5+ clubs, NF.

2                 GF, one of three types of hand:

                           (a)  6+ clubs without 4 cards in the other major;

                           (b)  balanced with 3 card support (i.e. 18-20 or 23+);

                           (c)  any game-going hand with 4+ card support.

Raise              Usually 4 card support, minimum, might be balanced or unbalanced.

2 over 1     Natural reverse, GF.

2 over 1     Not used at present - could be defined as certain hands with 5+ spades

2NT                Balanced (i.e. 18-20 or 23+) with exactly 2 cards in responder's suit.

3                 6 card suit with 3 card support for responder's suit.

3/3            Natural, strongly invitational.

3NT               Solid clubs, singleton or void in responder's suit.

After 1-1-1, responder rebids 2 with 11+ (4SF, GF), otherwise (with 7-10) chooses between 1NT, 2, 2 and 2.  Except over the last of these opener's 2 rebid is GF with 5+ spades (saying nothing about clubs).  After 1-1-1-1NT/2 opener rebids 2 with a strong unbalanced hand with clubs.

Opener's 2 rebid is a form of Odwrotka (a Polish Club convention).  Responder bids 2 with 4 cards in his suit, 2 with 5 cards or 2NT with 6+ cards.  Opener plans to rebid 2 with 4 card support, 2NT with 3 card support in a balanced hand or 3 with 6+ clubs.  If responder's second bid prevents this, the partnership must have a 9+ card fit in responder's major, so opener starts cue-bidding (3 or higher). 

Opener's rebids after 1 - 1NT

2                 Minimum unbalanced hand with clubs.  Responder may bid again with a                               maximum.

2                 Non-minimum unbalanced hand with clubs, no relation to diamonds.

2                 12-14 with 5-3-3-2 shape.

2                 5+ card suit, GF.

2NT              Natural, invitational (unabalnced with clubs).

3                Natural, invitational.


Opener's rebids after 1 - 2/2

2 (over 2)    4 card suit, usually balanced.  Might be unbalanced with clubs.

2                    4+ card suit, usually balanced.  Might be unbalanced with clubs.

2                    4+ card suit, any type of hand.

2NT                  balanced, no 4 card major.

3                    unbalanced with clubs, no 4 card major.

3/3               Splinter bids, non-minimum.

 Subsequent bidding is mainly natural.  Responder will often use 2NT as a waiting bid, in order to give opener a chance to describe his hand further.

Responses to 1

1/1          0+ points, 4+ card suit.  Might have diamond support.  Might have longer clubs                   with less than 11 points.

1NT            0-8 points, no 4 card major.

2             9+, natural, forcing to 2NT.  Might have a 4 card major if 11+.

2             9+, natural, forcing to 3.  No 4 card major.

2/2        7-9, 6+ card suit.

2NT            5-8, 4+ diamonds (Bergen-style, to fill the gap between 2 and 3).                        Opener may rebid 3 as a game try or sign off in 3.

3             Natural, weak.

3             0-4, 5+ diamonds.

3NT           11-13, all suits stopped, 3=3=3=4 or 3=3=4=3 distribution.

Rebids after 2, 2, 2 and 3 are similar to those in 2/1 and similar systems.

Rebids after 1 - 1/1

1 (over 1)     13-20 points, 4 spades, NF.  Might be 4=1=4=4 shape.

1NT                   18+ unbalanced, any distribution (except 6+4OM).  Might be 16-17 with                                   4 card support (if opener wants to be in game opposite 6+ points).                                        Denies a GF hand with 3+ card support.

2                   13-17, normally at least 5+4.  Occasionally 4+5 if the diamonds are                              very much better than the clubs.

2                   13-17, 6+ diamonds.  Might also be 5+4 after a 1 response.

Raise               Denies enough for 1NT, might sometimes be 3 card support.

2NT                GF, 3+ card support for responder's suit.

Higher bids are generally 15-17, natural and distributional.


Rebids after 1 - 1/1 - 1NT

2               6+ points, GF, waiting bid with virtually any shape.

2               0-5 points, most hands

2/2         0-5 points, 6+ card suit or 5 card suit with 0-1 diamond.

2NT             6-9 points, 4-3-3-3 shape.

3               0-5 points, NF, 6+ clubs, only 4 cards in the bid major.

Rebids after 1 - 1NT

Pass        13-17, denies 6 diamonds or 4 clubs.

2           Gazzilli.  Either 13-17 with at least 4-4 in the minors, or most 18+ hands.

2           13-17, usually 6+ diamonds.  Might be 1=4=5=3 or 4=1=5=3 shape.

2/2     5+ card suit (hence 6+ diamonds), F1R.

2NT         GF, 6+ diamonds.


Rebids after 1 - 1NT - 2

2           0-5, either 3 diamonds or 3=3=2=5 shape.

2/2     6-8, feature in suit bid, 4+ clubs

2NT         6-8, no major suit stopper, 4+ clubs

3           0-5, either 7+ clubs or 6 clubs with 1 or 2 diamonds.

3           6-8, 3=3=4=3 shape.

Note that the above rebids are somewhat different from those over Gazzilli when it follows a 1 opening.


Rebids after 1 - 2

2            5+ card suit, unlimited, might have a 4 card major if minimum.                                                    F1R: the bidding may stop in 2NT, 3 or 3.

2/2      Natural, GF, possibly 4-4-4-1 (2♠ denies 4 hearts).

2NT         Minimum 4=4=4=1, NF.

3           Natural, minimum, NF.  Might be 4=1=4=4 or 1=4=4=4.

3           6+ card suit, strong suit, GF.

3/3     Splinter bids in support of clubs, not 4-4-4-1.

Developments after a 1 opening

The 1 opening normally shows 13+ points (rule of 22) with a 5+ card suit, but can be 11-12 points with 4-5 in the majors.

In most cases, a partnership can use its existing 2/1 methods.  There are, however, two necessary changes from "standard" 2/1:

  • It's essential to use the Kaplan Interchange of the 1 and 1NT responses;
  • After a 1 or 1NT response, opener's cheapest rebid is Gazzilli.

It is also useful to employ both 2 and 2NT to show 4+ card support.  There's little value in using 2 as a Weak Jump Shift, especially as the 1NT response already shows 5+ spades.  This approach allows 3 and 3 to be played as natural, rather than as Bergen raises.


Responses to 1

1                 0-12 points, F1R, denies 5 spades.  Might have 3 hearts with 0-4 or 9-12 points.

1NT              0+ points, F1R, 5+ spades.

2/2          12+, GF, natural in principle.

2                5-8, 3 card support.

2                Jacoby-style, 4+ card support, limit raise (opposite 11-12) or better.

2NT              Bergen-style, 4+ card support, 6-10 points.

3/3           Natural, invitational.

3                Pre-emptive, 3-6 (including shortage points), 4+ card support.

3NT              13-15 balanced, stoppers in unbid suits, 3=3=3=4 or 3=3=4=3 distribution.

3/4/4     Splinter bids in support of hearts.


Rebids after 1 - 1

1NT          Gazzilli – either 11-16 with spades or most 17+ point hands.

2/2     13-16 with 4+ card suit.

2            13-16, 6+ hearts.

2NT          GF.

Other bids are natural, strong but NF.


Rebids after 1 - 1NT

2         Gazzilli – either 13-16 with clubs or most 17+ point hands.  Might be slightly less                     with spade support.

2         13-16 with 4+ card suit.

2         13-16, 6+ hearts.

2         11-15, 3+ card support.

2NT       GF.

Other bids are natural, strong but NF.


Outline of Gazzilli after a 1 opening

Responder usually bids the next step up with 7+ points.  After this, opener's rebid in his major suit shows the weak type and other rebids (showing 17+) are GF.

With 0-6 points responder makes the most descriptive higher rebid, which will often be 2 of opener's suit with a doubleton.

Opening bids of 2, 2 and 2

In MOSSO a 2 or 2 opening shows 9-12 points and either 6+ cards in the bid suit, or 5 cards with a second suit (usually 4 cards, but a 2 opening could be 5-5 in the minors). Another way of looking at it is that it shows a 5+ card suit with any shape except 5-3-3-2.

The MOSSO 2 opening is similar, but denies 4 spades.

It's fair to say that these opening bids aren't the most accurate part of the system. Responder often has to pass the opening bid and this can result in a poor 5-2 or 5-1 fit, with other pairs finding a better contract after an opening bid at the 1 level or an initial pass.  Even when responder is strong enough to bid, there is sometimes insufficient space for exploration, especially after a 2 opening.

On the other hand, with opener having 9-12 points, the hand is just as likely to belong to the opponents. Now they are the ones to suffer from lack of bidding space, especially if responder has support for opener's suit and can continue the preempt further.

MOSSO doesn't mandate opening 2, 2 or 2 with 9-10 points: opener always has the option of passing, especially with 5-4-2-2 shape.

The 2 opening is quite similar to Precision. The slightly narrower range in MOSSO is offset by the possibility that opener might have 5 clubs and 4 diamonds, with which most Precision players would open 1. These players can stick to their existing methods, although the recommended MOSSO approach is quite similar to traditional Precision. Using 2 as a relay (showing invitational-plus values) works quite well.

Life isn't so easy after a 2 or 2 opening. The next bid up is used as a relay, with a 2NT response showing 5+ cards in the suit above. This approach allows 4-4 major suit fits to be located after 2 (not necessary after 2), although subsequent bidding can still sometimes be difficult.

Responses to 2

2           Relay, at least an invitational hand.

2/2     NF, 5+ card suit.

2NT         5+ diamonds, F1R.

3          Preemptive.


Rebids after 2 - 2

2/2     4 card suit, any strength.

2NT         Minimum, 6 clubs or 4 diamonds.

3          6 card suit, maximum.

3          4 card suit, maximum.


Responses to 2

2          Relay, at least an invitational hand.

2          NF, 5+ card suit.

2NT        5+ hearts, F1R.

3          6+ card suit, F1R.

3          Preemptive.


Rebids after 2 - 2

2       4 card suit, any strength.

2NT     Minimum, 4 hearts.

3       4 card suit, any strength. Might sometimes be maximum, 6 diamonds, club feature.

3       6 card suit, minimum.

3       4 card suit, maximum.

Responses to 2

2           Relay, at least an invitational hand.

2NT        5+ spades, F1R.

3/3     6+ card suit, F1R.

3          Pre-emptive.


Rebids after 2 - 2

2NT           Any maximum hand. Responder can relay with 3 to discover opener's                                 second suit.

3/3       4 card suit, minimum.

3             6 card suit, minimum.



This article has been written in order to provide an introduction to MOSSO, highlighting the areas that are significantly different from 2/1.  I didn't want to make the article too long, but I've tried to provide enough information for people to try out the system.  I realize that more detail would be required for a serious partnership.

In particular, I've said nothing about handling intervention, although I'm happy to write a follow-up article on this topic if there is sufficient interest.  I am also willing to provide further information on particular sequences.

So, does MOSSO work?  So far I've only played the system for a few months, but much of my 2-3 years experience of SWIFT carries across to MOSSO.  The new MOSSO sequences seem to work well in practice and overall results so far have been encouraging.

What about the opening 2 bids?  For nearly two years I kept records of the SWIFT 2 bids.  The SWIFT 2 opening led to only a very small gain on balance and the significant number of poor results was one factor in the move to MOSSO.  The SWIFT 2, 2 and 2 openings all showed a healthy profit.  Partnerships therefore need not feel nervous about using these three intermediate opening bids.

It is probably impossible to design a system based around unlimited 1-level opening bids that doesn't possess a number of quirks.  There are several in MOSSO (e.g. opening 1 with a balanced 12-14 points with 5 hearts), but these don't seem to cause significant problems.  MOSSO has a number of advantages over natural systems such as 2/1, such as being able to play in 1NT with 18-20 balanced opposite a weak hand (via the sequence 1-1-1NT).  Also, constructive bidding is often easier in MOSSO because some NF 2/1 sequences become F1R in MOSSO and some F1R sequences in 2/1 become GF in MOSSO.

MOSSO has been developed as a serious bidding system, but it's also fun to play.  Why not give it a try?

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