In either case, the important thing is to make sure that the various possible hand types go well together.
The One-Bid-Or-Two principle is very relevant here. If opener has a pure two-bid hand, then he will be able to reveal which hand type he has with his rebid. But if he has a one-bid hand, he may be unable to add anything to the initial description except to deny a hand suitable for taking a second bid. So, although responder's bids must cater for all the possible hand types opener can have, it is opener's one-bid hands which you need to be most concerned about. The opening bid must provide sufficiently good information about the one-bid hands that responder will know what to do. This does not necessarily mean that responder must be able to place the contract immediately, but he must at least be able to control the auction.
The easiest way to do this is to make the one-bid hands homogeneous. That is, while the opening bid as a whole may be a multi-way bid with a variety of different options, it is a good idea for all the one-bid hands to be covered by a single hand type - or perhaps by a small number of homogeneous hand types. The reason is simple: responder needs to know immediately what he should do opposite a one-bid hand, and a homogeneous opening bid is the best way of providing immediate information. All of the ideas about what makes a good homogeneous bid apply here.
For the two-bid hands, homogeneity is not so important: it is possible to have different rebids showing different hand types. The Swedish 1C opening is an excellent example of this. The one-bid hands are very homogeneous, consisting of a single hand type (11-13 HCP balanced), whereas there is much more variety in the two-bid hands: any shape is possible for the strong option. Many other well-designed multi-way bids work the same way: they have homogeneity in their one-bid hands, but it does not extend to their two-bid hands.
One problem with this sort of opening bid is a lack of flexibility. The different hand types are very clearly separated. So, if opener has a hand which is supposed to be treated as a two-bid hand, it is important to follow up by actually making the rebid which shows the hand. Unfortunately, as we know, not all hands are "pure" examples of one-bid or two-bid hands. A balanced 17-count is certainly not a pure two-bid hand. But if you open a two-way 1C, then this hand is treated as belonging to the strong variant. So if you are unlucky enough to have LHO overcall 2S, say, and responder raise to 3S, you will be in a difficult position. If you pass then partner will play you for a weak balanced hand, but there is no safety in making a free bid either. The lack of homogeneity between the different hand types is the problem here.
So this sort of bid works best when the "strong" hand types are genuine two-bid hands - as pure as possible. Ideally, they should either have overwhelming high-card strength (20+ HCP should ensure that the hand is a two-bid hand) or be very distributional - though in the latter case you need to be careful that you can actually describe the shape well with your rebid. (Single-suited hands are best for this.) In practice, most systems will have to allow some dubious hands into their strong options because of a lack of better places to put them, but clearly the strong option in our favourite example (17+ HCP, any shape) is already rather light, and anything weaker than this would be really asking for trouble.
Typically, if the one-bid hands are going to be homogeneous, this would mean that there is a particular hand type which responder will play opener to have until proven otherwise. We would call this the dominant hand type. Obviously the dominant hand type in the Swedish 1C opening is the weak balanced hand, but the term also makes sense for natural bids. For example, playing a standard 5-card major system, the dominant hand type in a 1S opening bid is a minimum hand with precisely 5 spades. More generally, the dominant hand type would usually be the most frequent one-bid hand type that opener can hold. We can state a general "homogeneity principle" in these terms:
All the one-bid hands in an opening bid should be as
close to the dominant hand type as possible.
The idea from a previous post that the "average" length (or strength) promised by an opening bid should be as close as possible to the minimum length (strength) is really just a special case of this. But we can now see that the average should be taken over only the one-bid hands. Two-bid hands do not need to be close to the dominant hand type, provided that they are pure two-bid hands. With an "in-between" hand you have a slight problem - it may work adequately well to treat them as two-bid hands, but it would also be helpful to have them be fairly similar to the homogeneous one-bid hands, in case the auction prevented opener from showing the precise hand type.
Bids which have a wide range of one-bid hands, or where there is no single dominant hand type, are much more problematic. But they do exist, with the most obvious example being the multi-2D opening bid. A multi-2D shows a weak hand with either hearts or spades (possibly with other strong options which are genuine two-bid hands). Although the strength promised is the same no matter which major suit is held, clearly in terms of distribution this is not a homogeneous bid. In a case like this, you have to find particular reasons why the bid "works" - why should responder be able to cater for both hand types at once? In general there is no guarantee that it will be possible.
There are a few reasons why the multi-2D is an effective bid. In particular:
- It is a pre-emptive bid, and will hopefully cause even more problems for the opposition than it does for opener's side.
- It is highly likely that responder will have at least as many cards in the other major as he does in the suit that opener actually holds. If opener has hearts and responder has 3-card heart support then the partnership should probably be playing in at least 3H; provided that responder has at least three spades as well, he will know that it is safe to bid 3H because his support for a spade suit would be just as good.
- If this is one of the rare deals where responder is actually shorter in the other major, then the opponents will almost always have a fit there and probably ought to be playing in that suit. If they do bid that suit, then this will let responder know what is going on.
- Because opener has a long major, if the hand belongs to opener's side, the most likely denomination is opener's suit. So responder will not often need to find out much more information than what opener's suit is. If opener's suit was a minor there would be much more information needed, and this would be difficult to get since you are already a step behind by not knowing what opener's suit is immediately.