When opponents open 1NT and their partner responds with Stayman or Transfers, how do you play a double?
The conventional view when I was learning the game was that double showed a hand that would have doubled 1NT, as otherwise these hands were difficult to bid. Having said this, even amongst the top players, there are many who play the double as natural, showing the suit bid. Some combine the two, saying that double is either natural, or the first move on a strong hand.
The last option, whilst sounding to be a good compromise, is actually fairly unplayable, though I play it myself with some partners! However, if you add some methods in, it becomes a good compromise, allowing you to compete in diamonds, take penalties when they are due, and bid game as appropriate. The following is rather technical, so if you are not called Wightwick this could be a good point to skip to the next article!
The key is that double by responder is the normal action with 3 card support for partner's possible suit, and 7+ points. We illustrate over the two diamond transfer.
(1NT)-P-(2)-X,-(2)-X = 3+ diamonds, 7+ points (but not long hearts).
(1NT)-P-(2)-X,-(2)-2/3 = Fit jumps (5 spades, 3 diamonds); note no overcall of 1NT.
(1NT)-P-(2)-X,-(2)-2NT = 12-14, natural (taking a view that partner has the weak hand).
(1NT)-P-(2)-X,-(2)-3 = Constructive.
(1NT)-P-(2)-X,-(2)-3 = To play opposite the strong hand (taking the view partner has not got a weak hand with diamonds).
(1NT)-P-(2)-X,-(P)-2 = UCB, about 12-14 (other bids as before).
The important part of the system is how to continue after (1NT)-P-(2)-X,-(2)-X-(P)-? Basically `rebidding' your suit is weak, and all others are strong:
P = For penalties.
3 = Weak with diamonds (may have other suits as well, but too bad!).
2 = Natural, 4 or 5 spades usually.
2NT = Scramble, 16+ points (any hand with four card suits, or minimum with diamonds)
3 = 16+, natural, but minimum.
3 = Game forcing with a minor.
3 = Game forcing with six spades.
4m = 5-5 with spades and the bid minor (ie Roman Jump).
If the auction commences (1NT)-P-(2)-X,-(2)-P-(P), now all bids are strong, doubling being for take out (with Lebensohl), 2NT being used as a minimum strong hand with a minor, 3m is stronger but not forcing, the cue asks for a stop (ie based on a big minor suit hand else you would double), and 4m is a Roman jump as above.
A final sequence worthy of comment: (1NT)-P-(2)-X,-(P)-P-(2)-P = Weak with diamonds or strong wanting a penalty from 2 (partner can now double without 3 diamonds, eg 4225 shape).
You will note that the above does not cater for every hand. In particular you don't always take a penalty when the weaker hand has shortage in both red suits. Also. it is perhaps better to play (1NT)-P-(2)-X,-(2)-P-(P)-2NT as natural, about a 20 count, taking the view partner is not likely to be passing a take out double.
I should thank Ian Pagan for the basic idea of this system - the continuations are a joint effort.