Check-back is a mechanism whereby following a 1NT re-bid from opener, the responder can ask opener to define his no-trump range more accurately and also show additional features (it can also be used after a 2NT rebid).
Check-back evolved from Crowhurst (developed by Eric Crowhurst) which catered for the wide ranging 12–16 1NT rebid, but check-back is now associated with the more modern 15-17 1NT rebid. The basic principles are the same in either treatment.
(One reason why a 15-17 rebid has become popular is that a 2NT rebid is now 18-19 points and effectively game forcing, and hence dispensing with the awful Acol 19 point 3NT rebid).
Details differ, but the basis is that following opener’s 1NT rebid (15-17 points), a 2♣ bid by responder asks opener to define his hand in terms of minimum (15, 16(poor) points), or maximum (16(good), 17 points).
Responder’s points will normally be in the 7–9 range (but it can also be used on higher point hands to assess the best game contract, and also to consider slam possibilities opposite an appropriate maximum response from partner)
Opposite any maximum response it is game forcing.
The corollary is that if responder does not use the 2♣ check-back bid, any alternative bid tends to show weakness (some partnerships may treat this differently) – 5-7(poor) points.
Opener’s Responses to 2♣
Lower range (15, 16(poor) points)
Support responder’s suit with 3 card support
(e.g. 1♦ - 1♠ - 1NT - 2♣ - 2♠…)
Bid any new suit below 2NT
(e.g. 1♦ - 1♥ - 1NT - 2♣ - 2♠…) (this is not a reverse from opener)
Re-bid own suit with 5-card suit (with 5 card majors, good 5 or 6 card suit)
(e.g. 1♥ - 1♠ - 1NT - 2♣ - 2♥…)
If neither (a), (b), nor (c), bid 2♦
(e.g. 1♣ - 1♥ - 1NT - 2♣ - 2♦…)
Upper range (16 (good), 17 points)
Support responder’s suit by bidding it at the 3-level.
(e.g. 1♦ - 1♠ - 1NT - 2♣ - 3♠)
With extra length in own suit, re-bid suit at 3-level
(e.g. 1♥ - 1♠ - 1NT - 2♣ - 3♥… shows a 5-card suit or 6-card if playing 5-card majors)
With second suit, bid suit at 3-level
(e.g. 1♣ - 1♥ - 1NT - 2♣ - 3♠… shows a 4-card spade suit
With none of the above, bid 2NT
It’s important that if there is a choice of the three above options(a-c), the appropriate ones must be bid in sequence, with a view to showing any other option in the subsequent bidding(e.g. 1♦ - 1♠ - 1NT - 2♣ - 3♦ - 3♥ - 3♠ - 3NT – 4♥)…. Opener now has 16 or 17 points, and in sequence has shown 5 diamonds, 3 spades, 4 hearts, and has chosen not to reverse in hearts.(This approach avoids confusion in sequences such as 1♦ - 1♠ - 1NT - 2♣ - 3♣ - 4♦. The 4♦ bidder cannot now be cue-bidding agreeing spades, nor can he be asking opener if he has a five card diamond suit – yes he has, together with four clubs. Responder is just showing diamond support, inviting a cue-bid for a possible slam. Moreover if responder had bid 4NT instead of 4♦, this would be key-card in clubs)
If responder does not use check-back 2♣, and instead bids:
A jump response to the 1NT (including 3♣), usually shows a six card suit 5,6, 7(poor) count. Invitational but not forcing.
Any other natural suit at the two level. This tends to imply a 6-4 distribution, i.e. prepared to play at the three level in the 6-card suit. With most other distributions, he would be inclined to pass 1NT.
Examples: (where the sequences differ between 4 and 5 card majors, these are indicated).
((a) – (e) North has a ‘weak’ 1NT rebid)
a)♠ A72b)♠ A7c)♠ A743d)♠ A3e)♠ A7
♥ KJ532♥ KQ532♥ K5♥ J7642♥ J7642
♦ A86♦ A86♦ AQ864♦ AK5♦ AK5
♣ K4♣ Q43♣ Q4♣ K104♣ K104
♠ KJ843♠ K9843♠ K985♠ Q9843♠ Q109843
♥ 64♥ 64♥ AJ64♥ K9♥ K9
♦ K97♦ K97♦ 62♦ 964♦ 964
♣ J63♣ K62♣ 985♣ QJ8♣ QJ
a) 5-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♠ - pass North shows a minimum and 3-card support for partner. If South had only four spades he would bid 2NT which North would pass. He could bid 2♥ with a good 5-card or 6-card suit.
4-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♥ - 2♠ - pass North shows a minimum and also his 5-card heart suit.
b) 1♥ - 1♠ - 1NT - 2♣ - 2♥ - 2♠ - 2NT - pass. North shows a minimum and good hearts (even playing an original 5-card major suit, the heart suit is worth repeating due to the good quality). If South had three card heart support, he would pass 2♥, or possibly bid 3♥ further inviting North.
c) 1♦ - 1♥ - 1NT - 2♣ - 2♠ – pass. South correctly bids his 4-card hearts before the spades. North shows a minimum and four spades. With the fit, South passes.
d) 5-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♦ - 2NT – pass By bidding 2♦ (alertable), North shows his minimum and also denies any useful feature (neither good hearts nor three spades). No point in South repeating his five-card spade suit, he knows North doesn’t have support having by-passed 2♠.
4-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♥ - 2♠ - 2NT – pass North shows his minimum and now five hearts. South must now repeat his spade suit (North hasn’t denied three spades).
e) 5-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♦ - 2♠ – pass North shows his minimum and denies any useful feature. South now repeats his six-card suit which North now passes (North knows that it would be pointless South re-bidding his 5-card suit).
4-card majors: 1♥ - 1♠ - 1NT - 2♣ - 2♥ - 2NT - 3♠ – pass Unlike the situation with 5-card majors, North doesn’t know that South has a six-card suit because he himself has not denied a 3-card spade suit. With his spade holding, South prefers spades to a no-trump contract.
((f) – (k) North has a ‘strong’ 1NT rebid)
f)♠ 76g)♠ J76h)♠ K2i)♠ K75j)♠ 86
♥ AQ43♥ A9♥ AK953♥ AK5♥ AQ532
♦ AK852♦ AKJ106♦ AK8♦ K643♦ AK75
♣ A4♣ A86♣ 864♣ K10♣ A94
♠ Q10985♠ Q10985♠ A984♠ AJ984♠ K9754
♥ K864♥ K864♥ QJ♥ Q764♥ K6
♦ 97♦ 97♦ J107♦ A7♦ Q9643
♣ K3♣ K3♣ 9752♣ A5♣ 6
f) 1♦ - 1♠ - 1NT - 2♣ - 3♦ - 3♥ - 4♥ By jumping in diamonds (i.e. bidding above 2NT), North shows a maximum and a five card diamond suit (in sequence, rather than the 4-card heart suit). South shows his hearts, and North bids the heart game.
g) 1♦ - 1♠ - 1NT - 2♣ - 3♦ - 3♥ - 3♠ - 4♠ Similar to (f), North knows partner must be 5-4 in the majors (with 4-4 he would have bid hearts first), but can now support with the 3-card spade suit. With better spades he may well bid 4♠ rather than 3♠. (In this hand, 3♠ is preferred showing a poor three card suit. South’s spades are just about good enough to prefer 4♠ to 3NT. With say ♠109875, he would probably prefer 3NT)
h) 1♥ - 1♠ - 1NT - 2♣ - 3♥ - 4♥ When North shows a good 5-card or a 6-card suit, even with the heart doubleton, South should prefer 4♥ to 3NT.
i) 1♦ - 1♠ - 1NT - 2♣ - 3♠ - 4NT …… 6♠ South uses 2♣ check-back to investigate slam possibilities. When North is able to support spades, the correct slam can be bid.
j) 1♥ - 1♠ - 1NT - 2♣ - 3♦ - 3♠ - 3NT - 5♦ Even with the known diamond fit, South still repeats his spades – North hasn’t denied 3-card spade support. If North did have 3-card spade support, he would bid 4♠ in preference to 3NT.
k) 1♥ - 1♠ - 1NT - 2♣ - 2NT – 3NT No major (nor minor) fit, so North just re-bids 2NT
((l) – (p) South has insufficient points for a check-back 2♣ bid).
l)♠ AJm)♠ AJn)♠ AJ6o)♠ AJ63p)♠ AQ63
♥ 873♥ Q73♥ 83♥ 8♥ J3
♦ K54♦ K54♦ KQ4♦ AK54♦ AK5
♣ AK1084♣ AK1084♣ AK1084♣ AK1084♣ Q973
♠ K82♠ K82♠ Q984♠ Q854♠ 108
♥ K109642♥ K109642♥ KJ9642♥ KJ9642♥ Q764
♦ 976♦ 976♦ 9♦ 9♦ 9
♣ 63♣ 63♣ 963♣ 63♣ KJ8654
l) 1♣ - 1♥ - 1NT - 3♥ - pass South hasn’t used a check-back 3♣ with 6 points, so the jump bid in hearts is invitational. North declines.
m) 1♣ - 1♥ - 1NT - 3♥ - 4♥ ….whereas, North with his extra useful 2 points accepts.
n) 1♣ - 1♥ - 1NT - 2♠ - 2NT/pass South’s 2♠ bid is not strong (he hasn’t used check-back) – shows 6, 7(poor) points. North either passes (preferred) or bids 2NT.
n) 1♣ - 1♥ - 1NT - 2♠ - 3♠ - 4♠/pass ….whereas with reasonable 4-card support and a singleton he’s worth a single raise. Playing teams South should probably raise to four, but be content with three at pairs. If North had a maximum (or good16) (e.g. ♦A instead of ♦K), he would raise to 4♠ himself.
o) 1♣ - 1♥ - 1NT - 3♣ - pass South hasn’t used check-back so he bids a weak 3♣ (6-card suit).(Even playing a short club opening, I would probably still bid 3♣ given the quality of the club suit)