What are the preconditions for a trump promotion in bridge?

My understanding is that there are two main conditions. The first is that the defense has a long suit with which they can set up a "ruffing finesse," usually against the declarer's trumps by leading through a newly created void (usually after a lead or two).

The second condition seems to be when the defense has a number of "intermediate" trumps, typically ranging from Q to 8. (If the defense had four trumps 5432, a promotion wouldn't work, and if the four defensive trumps were AKQJ, it wouldn't seem to matter.) With a promotion, a defender uses an intermediate trump to force out a higher trump to promote partner's intermediates.

Is this second precondition in fact the right one? And if so, how do you, a defender, detect the precondition either when making an opening lead (West) or responding to one (East)? Is it because you see a lot of low trumps in dummy and some intermediates in your own hand? And then do you infer that if partner has one or more trumps that they are likely to be intermediates?

• This is far too broad Tom - as in any card-game coup, the essential precondition is an imposition of zugswang, the compulsion to move (first, and suffer consequential severe disadvantages). If you are talking about how one recognizes such a condition that is because one is skilled and counted the opponents' hand. If you are actually asking about when to suspect this when choosing an opening lead, ask that question instead of this one.. Feb 6, 2016 at 13:02
• Expert bridge players don't think this way; there is no magic check-list of coups and strategems that they review in their head as they decide on a play. Rather they have studied these play sequences extensively, and at the table concentrate on counting the opponents' hands, simply recognizing patterns as they are spotted. The underlying principle is always about maneuvering the sequence to impose zugswang on the opponent before it is imposed on you - someone is always under compulsion to make a next play. Feb 6, 2016 at 13:07
• @PieterGeerkens: Amended the question per your suggestion. Feb 6, 2016 at 17:29

The Bridge Encyclopedia identifies 4 situations in which trump promotions ("the creation of trump tricks by forcing the premature use of trump cards by the opposition").

• Uppercuts - ruffing high to force opponent to overruff, thus promoting a trump trick in partner's hand.
• Establishing long tricks in trumps by forcing opponent to ruff - as in a forcing defense.
• Coup en passant to create a positional trump trick. Example:

``````      K
-
-
2
A           Q
-           -
-           A
A           -

J
-
2
-
``````

With spades as trumps and the lead in the south, if declarer (south) leads a trump, they lose both tricks. But if they lead a diamond, the spade King will be scored en passant - either west will trump and declarer will discard from dummy, or west will discard and declarer will ruff with the king.

• A positional overruff threat. For example, if south holds KQx in trumps and west holds AJ, playing on trumps will lead to west taking a single trump trick. If instead east plays on a side suit in which south and west are both void, south must ruff high to prevent an overruff with the J, but this establishes the J as a second trump trick (as long as west does not overruff with the ace!).

• The fourth case is even more interesting when West holds AJx in trumps, and must under-ruff South's ruff with the K or Q in order to preserve the extra trick. Feb 6, 2016 at 18:43