[Liversidge]

I play Acol. With one partner we have just started playing negative doubles, with the other less experienced partner we don't play it. I have good (though varied!) references on the negative double, except for what to do if the bidding goes `♦ - (2♣), and I can't find a lot on what responder's requirements are in terms of suit length after an overcall when not playing negative doubles.

First of all, using the negative double, I understand that I need a minimum of 6 HCP to double if my bid would have been at the 1 level, and 8 HCP if it would have been at the 2 level. I can't find any guidance on when the bidding goes 1♦ - (2♣), when a negative double shows just one major. I assume that you don't bid the negative double here unless you have a backstop response if partner bids the major you don't have, but shouldn't I also need a bit more than 8 HCP as I may well have to rebid at the 3 level?

Secondly, if playing with the partner who does not use the negative double, I assume that after 1♦ - (2♣) a bid of 2♠ requires 5 spades and 10+ HCP, but for any other sequence where opener's partner's bid is at the 2 level after an overcall, can the response be in a 4 card suit? For example, 1♠ - (2♦) - 2♥. With my more experienced partner I would make a negative double with 10+ HCP. If I can bid hearts with four cards, why is the negative double a superior bid? What additional information does it give partner?

[BillPatch]

Responding to OP.
1. Since modern acol is typically played with the weak NT at any vulnerability, the 1♦ promises either extra strength or extra distribution, so with the normal minimum of 8 hcp, as specified in Bergen. Negative Doubles for Acol Players. ed. Tim Bourke. Not the same as Standard American.
2. I assume so. If you're willing to play the Moysian fit(4-3). Do not waste too much time trying to develop detailed understandings with partners who have not learned negative doubles.
3. If a player makes a negative double rather than the 2 over one there is the negative information that partner does not have 10 hcp and a 5 card suit.

[steve2005]

1♦-2♣ is a special case, it is often undiscussed even by experienced partnerships.
2♣ causes some problems.
It raises the bidding as much as possible without preempting
For a negative double responder needs both majors unless you agree to double on 4-3 hands

Often partnerships have not defined what strength 2♥/2♠ means,

It is often a good tactic by responder to raise opener (especially in Acol) when values are questionable or doesn't have an ideal neg X

[wank]

As was alluded to above, all the books you'll see assume you're playing 5 card majors, but more importantly strong nt. As weak nt, 4 card majors is such a minority method globally there are no decent books about it as far as i'm aware.

If you play weak nt, doubles at the 2 level are geared towards getting to 3nt when opener has a strong NT rather than showing majors.

Weak nt is very difficult to play. Of course it's easy when you open 1nt but the extra values you might hold (in hands shape unsuitable for reopening) when you don't open 1nt mean responder has to bid more over intervention than strong NT bidders do to cater to those strong hands.

[Liversidge]

 BillPatch, on 2015-August-23, 14:01, said:

so with the normal minimum of 8 hcp, as specified in Bergen. Negative Doubles for Acol Players. ed. Tim Bourke.

£66 on Amazon!!

[rmnka447]

Your questions about bidding when not playing negative doubles highlights why they came into being in the first place. They provide a way for finding a major suit fit without forcing you to bid a 4 card major suit at the 2 level. This often makes it easier for opener to assess the major fit properly.

Take the auction you suggest -- 1 ♠ - (2 ♦) - 2 ♥ - ?

If opener has 4 ♥s, there's no problem in raising. But if opener holds only 3 ♥s and you can be bidding on only 4 ♥s, a raise may not be so clear. It's especially true if opener holds length in the opponent's suit. Holding say ♠ AKxxx ♥ Qxx ♦ xxx ♣ Kx, raising ♥s is risky because 3 rounds of ♦ forcing the 4 card suit to ruff may cause your side to lose control of the trump suit and the hand. OTOH, if opener fails to raise, he/she may find out later that responder held 5 ♥s and they missed their fit.

Obviously, if you decide to reserve the 2 ♥ bid for hands with 5+ ♥ without negative doubles, then you risk losing out on finding 4-4 fits on many hands where opener can't find a ♥ bid.

So, there are problems with 2 level free bids however you decide to play them when you don't play negative doubles.

However, playing negative doubles, responder negative doubles with 4 ♥, so the 2 ♥ bid promises 5+ ♥. Now opener has an easy raise with 3. Yet at the same time, after a negative double, a 4-4 ♥ fit can still be found when it exists.

[BillPatch]

 steve2005, on 2015-August-23, 15:30, said:

1♦-2♣ is a special case, it is often undiscussed even by experienced partnerships.
2♣ causes some problems.
It raises the bidding as much as possible without preempting
For a negative double responder needs both majors unless you agree to double on 4-3 hands

Often partnerships have not defined what strength 2♥/2♠ means,

It is often a good tactic by responder to raise opener (especially in Acol) when values are questionable or doesn't have an ideal neg X

Agreement to reopen only the perfect 4-4 or the imperfect 4-3 majors is too conservative for Bergen, Bourke. Op.cit. p. 44. Their examples for Imperfect doubles on this auction. ♠ A9854 ♥ KQ7 ♦ 98 ♣ 865 &
♠ A2 ♥ KQ75 ♦ J643 ♣732
Note that the 2-4 hand has 10hcp and 4♦ in order to rebid 3♦ when partner rebids the wrong major.