A very complicated question I recently received, not reproduced because of the complexity, brought up an aspect of theory that may be of interest to some.
There are occasions when you just plain do not seem to have space to tell your tale. In such auctions, a little bit of general theory can be useful.
The Serious 3NT call and Last Train to Clarksville are often used to fill the gap between what can be directly shown and what must be shown in “general terms.” Obviously, if you can tell you tale with one final cuebid, or with two prepared cues that you will be able to make when it matters, that is your solution. Equally, if you do not tell your tale with that one final cuebid, or two prepared cuebids, you must have a hand that cannot be completely described in that manner. This may seem obvious, but the subtlety is often missed.
When you need a “general terms” auction, it is a good idea to have default understandings as to what specific “general cuebids” (Serious 3NT and Last Train) mean. One default that I often use is that a Serious 3NT call, a call that shows “extras” in general terms, tends to be based upon good trumps when neither I nor partner could show good trumps any other way. For instance, if a major is agreed at the three-level, there is no ability to cuebid trumps. Thus, a Serious 3NT often is justified because of good trumps.
Conversely, the “companion” default is that Last Train, a bid that asks for “extras,” tends to be the call used to ask about external controls that may still be needed. Thus, you would tend to bid 3NT when you need to express the strength of your internal values (trump quality), but you would tend to use Last Train (or rely upon partner to use Last Train) to ask about the strength of the unknown external values (controls).
By default “tendencies,” this does not mean that a Serious 3NT or a Last Train call always is defined according to these defaults. Rather, you “think trumps” when interpreting a Serious 3NT and “think outside controls” when responding to a Last Train invite, always governing your interpretation on the preceding auction. The “defaults” really are designed to guide a partnership when ambiguities develop or when deciding between two courses that seem equally plausible.
A similar problem might occur in the context of an auction where, perhaps, trump quality is completely known. For example, one person bypasses 2NT (two trump honors) and then someone cues trumps to show the third top trump honor.
However, the four-level may provide insufficient space to tell some vital part of your story. This often happens when you have a holding that would justify cuebidding a suit twice if you had space; for example, showing two top honors in partner’s suit when you have not yet had a chance to show any top honor in his suit. These two cuebids might be collapsed into justifying a Serious 3NT call because, in a sense, the two cards of value are “touching” and not otherwise biddable.
Similarly, you may have a desire to cuebid two suits that are touching. Consider having the need to cuebid clubs (4♣) then hearts (4♥). This will be easy if you expect, or will need, a 4D cue from partner, right? Well, what if you would like to cue clubs and diamonds? If you cue 4♣, partner’s next call per force will preempt you out of ability to cuebid your value in diamonds. This is bad. Again, however, 3NT may solve the problem, insofar as 3NT again is handling two “touching” values.
So, when deciding whether to use a Serious 3NT call or not, consider that another default tendency is for 3NT to handle “touching” values. Conversely, keep that in mind when interpreting a Serious 3NT call from partner.
Note that both of these defaults have a common sense logic to them. We often tend to overstate our strength if we hold unexpected strength in trumps or in partner’s side suit because we expect partner to be conversely cautious because of his obvious weakness in trumps or in his side suit. Using Serious 3NT makes sense as a practical solution to this recurring problem. Articulating this theory and recognizing it in practice should help to define ambiguous auctions in a meaningful way.