Suppose partner opens 1♦ and you have a hand such as:
| Kxx |
| xx |
| Qxxx |
| Q10xx |
It is a bit much to jump to three diamonds with no shape and partner possibly having only three diamonds, so, playing inverted raises, this hand would probably respond 1NT. There are two important reasons that a 2♦ response is likely to work out better.
The first is that the 1NT response is likely to lead to any notrump contract being played from the wrong side. Maybe the two hands are something like this:
| Q10x | Kxx |
| AQx | xx |
| AKxx | Qxxx |
| KJx | Q10xx |
There is a much better chance of making 3NT when played by the West hand. Since the 1NT response with four card support will be made on a weak hand with no four card major it is quite likely that the hand will lack good stoppers in the majors and a NT contract will play better from the other side after an auction such as 1♦-2♦-3NT.
The second reason to bid 2♦ is that supporting immediately allows partner to compete when it is correct to do so. Maybe the full hand is something like this:
| J10xx | ||
| 109x | ||
| Kx | ||
| 98xx | ||
| xx | Kxx | |
| AQxx | xx | |
| AJ10xx | Qxxx | |
| Kx | Q10xx | |
| AQxx | ||
| KJxx | ||
| xx | ||
| AJx |
South will double the 2♦ response and West can bid an immediate 3♦. This may or may not shut out the opponents, but you are assured of a plus score since 3♦ makes and 3♠ is down at least one. If South had responded 1NT instead, South would double. It isn’t really safe for West to bid 2♦ because partner could easily be 3325 and with the doubler likely short in diamonds as well it could get very messy. So when West passes and North bids 2♠, East has to guess whether to compete to 3♦. Maybe the full hand is:
| J10xx | ||
| 109x | ||
| KJxx | ||
| xx | ||
| xxx | Kxx | |
| AQxx | xx | |
| A10xx | Qxxx | |
| Kx | Q10xx | |
| AQx | ||
| KJxx | ||
| x | ||
| AJ98x |
You will probably be down two doubled in 3♦ and the opponents’ 2♠ may not make either. If you play a weak notrump West will not have that hand, however if the king and ten of diamonds are switched West will have a 1♦ opening and both 2♠ and 3♦ are still down.
There is plenty of space to handle stronger hands with support for partner’s minor because we can use jump responses. Traditional strong jump shifts don’t occur very often and weak jump shifts have little advantage over just bidding and rebidding the major suit.
I recommend the following structure over a 1♦ opening:
| 2♦ | Four card support and about 5-9 HCP |
| 2♥ | Five spades and four hearts with about 7-9 HCP |
| 2♠ | Four card or better support and about 10+ HCP |
| 2NT | 16+ balanced |
| 3♣ | Five card support and about 7-8 HCP |
| 3♦ | Five card support and 4-6 HCP |
I like to use the 2♥ response for a hand such as Axxxx KJxx xx xx because otherwise a 1♠ response and 2♦ rebid from partner will make life difficult. Partner could have either of the following hands:
| x | x |
| AQxx | xxx |
| AKxxxx | KQJxxx |
| xx | AKx |
Opposite the first hand I want to be in four hearts. Opposite the second I would prefer to be in 2♦ but can live with playing 2♥ or 3♦. But after a forcing and unlimited 2♥ rebid partner really has to drive to game with the second hand. There is also a possibility that partner could have 1444 shape and we can make 9 or 10 tricks in hearts but could be playing 2♦ if I respond 1♠ and partner rebids 2♣.
I also like to have a bid for strong balanced hands as these are hard to describe accurately, for example:
| xx | Kx | AQxx | ||
| Ax | or | Ax | opposite | Kxxx |
| KQxxx | KQxxx | Ax | ||
| Axxx | Axxx | KJx |
After 1♦-1♥-2♣, East would like to stop in 3NT opposite the first hand but 6NT has good play opposite the second. Fourth suit forcing can be used but this tends to show doubt about strain, rather than necessarily extra values. Responding 2NT with 16+ balanced solves this problem and a natural 2NT response is not really needed as we can respond either 2♣ or 2♠ with those hands. I don’t recommend that you play 1♦-2♣ as forcing to game even if you normally play that a two over one is game forcing.
We also have two ways to show five card support. Since we are already at the three level with no space to investigate further without going past 3♦, it makes sense to have narrower ranges in case partner is considering bidding on.
All of this does mean that our forcing raise is two steps higher. However there is still plenty of space to investigate stoppers below 3NT.
If the opening bid is 1♣, you can do the same one step lower or rearrange things a little if you prefer, e.g.
| 2♣ | Four card support and about 5-9 HCP |
| 2♦ | Four card or better support and about 10+ HCP |
| 2♥ | Five spades and four hearts with about 7-9 HCP |
| 2♠ | Five card support and about 7-8 HCP |
| 2NT | 16+ balanced |
| 3♣ | Five card support and 4-6 HCP |
A final point is that a single raise, 1♣-2♣ or 1♦-2♦, does not deny a four card major. Though you will often respond in a major, there are considerable tactical advantages in bypassing a major to raise partner’s minor, especially when the major is hearts. If your side has a 4-4 heart fit and you have support for partner’s minor suit, there is a good chance the opponents can make a spade contract. Maybe they can still find it if you raise, but your LHO opponent may not be willing to overcall at the two level, or may have a hand that cannot double for takeout due to short hearts, for example:
| Jxxx | ||
| Axx | ||
| Jxx | ||
| Q10x | ||
| Q10x | xx | |
| KJxx | Q10xx | |
| AKxx | Qxxx | |
| xx | Kxx | |
| AKxx | ||
| xx | ||
| xx | ||
| AJxxx |
East-West can make eight tricks in either red suit, while North-South can make nine in either black suit. If East responds 1♥ to West’s 1♦, South will double and North-South will go plus in a spade contract or defending 3♥. If East instead raises to 2♦, it may go all pass. East-West will certainly not be upset to score 90 in 2♦ instead of 110 in 2♥.
