The re-popularization of this lead from the era of Whist is attributed to Mr. Sven Welith and Mr. Seth Wenneberg, both from Sweden. Similar to the rule of eleven, which may determine the play of a card by partner, who knows that the lead card is the fourth highest card down as per partnership agreement, the rule of twelve is a mathematical calculation from the days of playing Whist when the lead card is the third highest card.
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For more than 50 years, Mr. Sven Welith was one of the key figures in Swedish bridge, as a player, author, editor, writer and debator. His weekly Saturday column in the Scanian newspaper Skånska Dagbladet, which he wrote for thirty-two consecutive years, was widely read and discussed by players all over Sweden. Mr. Sven Welith died in the year 2001. He never wrote his memoirs, but he left a large bridge library. Using that as a base, a group of Scanian writers (Mr. Göran Gjerling, Mr. Hans-Olof Hallén, Mr. Anders Wirgren, Mr. Mats Nilsland, and Mr. P. D. Lindeberg) have written the history of Scanian bridge, much of it in Mr. Sven Welith's own words.
Note: Any additional information as to the bridge personality of Mr. Seth Wenneberg, especially photographic material, would be greatly appreciated.
The rule of twelve states that the player should subtract the number of the card from the number 12, and the result obtained is the number of higher cards than the one led in all of the other three hands. The partnership agreement is that the opener is permitted to open a Major suit with a minimum of four cards, which is standard in many bidding systems, especially Acol.
| Declarer: |
South |
| Contract: |
4 Spades |
| Vulnerability: |
None |
| Lead: |
4 of Hearts |
If the declarer determines that the 4 of Hearts is the third highest card, as per partnership agreement of East-West, then the declarer subtracts the number of the card, which is 4, from the number 12, then the declarer knows that there are 8 higher cards in his hand, the dummy, and the hand of East. Declarer will plan the play according to this information.
If East is certain that his partner has led the third highest card, then East will also play accordingly. In the above example East will play his Jack of Hearts.
However, in the configuration below:
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| Dummy |
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K107 |
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| West |
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Q96 |
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| West |
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AJ82 |
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West leads the 6 of Spades. East, knowing that the lead is the third highest card subtracts the number 6 from 12 and discovers that there are 6 cards higher in his hand, in dummy, and in the hand of the declarer. East has 3 and the Dummy has 3 = 6 higher cards. Declarer can have no card higher than the 6 of Spades in his hand. Since East holds: AJ82 and the 2 is the lowest card, then East knows that the declarer must have three Spades and that these three Spades are: 543 by deduction.
Therefore, if declarer plays the 7 of Spades from the dummy, East plays the 8 of Spades. However, if the declarer plays the 10 of Spades from the dummy, East then plays the Jack of Spades. And if the declarer plays the King of Spades from the dummy, East then plays the Ace of Spades. East-West take four Spade Tricks in a No Trump contract and three Spade tricks in a suit contract.
If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.