RESPONSES TO OPENING 1C

PassVery weak (0-5 points), no desire to shut out opponents.
Double of suit overcallTake-out if below 4S. To make a takeout double of an overcall and then pull partner's response when they do take it out is non-forcing with at least a five-card suit, since an immediate bid would have been forcing. (The logic is different after 1NT openings.)
Double of no-trump overcallPenalties
Redouble10+, wants to double for penalties, often a misfit. During the subsequent auction, the partnership has one standard takeout double "in the bank". This is in order to distinguish between a hand that simply wants to compete (will pass and wait for partner to make a takeout double) and one with game-forcing strength (will bid directly, forcing).
Minimum cue bid of overcall where the partnership can still stop in part-score; i.e. below 3 of opener's suitUnassuming Cue-Bid, with trump support and intermediate points. (Might occasionally be a preliminary move on a much stronger hand.)
1D, 1H, 1Snatural, one-round force
1NT after overcallNatural, constructive, about 7.5-10 points and denying four cards in any unbid major. Good holding in the opponents' suit, preferably at least one and a half stops.
1NTA balanced hand with club support that doesn't have a four-card major, is too weak for 1C 2C and doesn't want to bid 1C 3C.
New suit at 2 level after 1NT overcallNatural, non-forcing and to play, because a hand with game-going strength would have doubled.
Raise to 2Inverted Minor, 4+ trump support, denies a five-card major, forcing to 3m, 10-ish points or stronger.
Raise to 2 after overcallWeak, with trump support. If only three, had no better bid.
Raise to 2 after doubleWeak, promises no strength at all
2NT11-12, balanced, would have raised a weak 1NT to two. Denies a four-card major and four of partner's suit, so by inference must have at least four of the other minor.
2NT after doubleIntermediate jump raise in partner's suit. (Might occasionally be a preliminary move on a much stronger hand.)
2NT after overcallNatural, constructive, about 11-12 points. Good holding in the opponents' suit, preferably at least one and a half stops.
Jump shiftStrong six-card suit, 16+ points. Still applies after any intervention except a 1NT overcall.
Jump shift by passed hand or after 1NT overcallFit-Jump, two-suited, at least 5-4, trump support for partner. Forcing and normally shows an 8-loser hand or so, without enough strength to go to game.
New suit response from a passed hand above 2 of opener's suit (after opponents' intervention)Whatever the same bid would have meant without the intervention, e.g. pass (pass) 1C (1S) 2H is a fit-jump in hearts, just as it would have been without the overcall.
Jump raiseInverted Minor, 4+ trumps, denies a four-card major, weak. More informative than the equivalent Inverted Minor raise of a 1D opening bid, since the existence of the 1C 1NT alternative (also showing a club fit) means that partner has actually chosen to pre-empt instead of merely being forced to jump against their will by the bidding system.
Jump cue bid after overcallSplinter
Unnecessary jump shift up to Splinter LevelSplinter, denying a 4 card major. If the splinter is in a major, then by inference must have at least nine minor-suit cards. However if the splinter is in the other minor, then must have at least six-card trump support in a 6331 hand.
3NTstrong no-trump (i.e. balanced 15-17) with four-card trump support.
Raise to 4mMinorwood
Game raise (opponents silent)Shows shape rather than points, might be pre-emptive.
Game raise (contested auction)To play.
Jump shift to Blackwood LevelExclusion Blackwood
Jump shift to Grand-Hunting LevelComplete two-suiter. If the partnership had previously bid more than one suit and so there's ambiguity about which suits are being promised, then the other one is the first-bid suit of the player who just jumped.

RESPONSES TO AN OPENING 1C AFTER A NATURAL 2C OVERCALL, PROMISING CLUBS

Passeither (a) weak, or (b) a stronger but not game-going hand that would like to compete. Partner can always reopen with a takeout double.
Double8+ points, theoretically takeout but in practice any hand that wants to give partner the chance to pass for penalties.
New suit at 2-levelgame-forcing, natural, playing strength rather than defensive values.
New suit at 2-level if passed hand6-card suit, 6+ points, standard Weak Two continuations.
2NTtake-out, game-forcing
2NT if a passed handtake-out
3Cprobe for 3NT
New suit at 3-level6-card suit, 16+ points
New suit at 3-level if passed hand7-card suit, weak
3NTto play

DEFENCE TO 1C

Any bid in the pass-out seatA king weaker than when bid directly.
DoubleOne of two hand types. DEFAULT ASSUMPTION: take-out, opening strength, support for unbid suits. This is a "say it once and shut up" bid that thereafter leaves all competitive decisions to partner and the doubler is not expected to bid again unless partner finds a bid that asks them to do so. To do so shows extreme strength (17+) and previous assumptions about shape no longer apply. NOTE: this bid promises proper opening values (i.e. you'd been going to open the bidding if the opponents had passed) AND support for the unbid suits. Opening a 4441 10-count "because the shape is perfect" is a violation of all that is good and will cause cancer in kittens.
Suit overcall5-card suit, strength depends on vulnerability and level
Jump suit overcallWeak Two, 6-10 and a 6-card suit
Suit jump in the pass-out seat10-14 actual points (i.e. no transferred king), 6+ trumps, denies a four-card major side-suit, like a fourth-seat 2H opening.
Suit jump in spades in the pass-out seat8-12 (i.e. no transferred king), 6+ trumps, denies four hearts, like a fourth-seat 2S opening.
Greater jump suit overcallPre-emptive
1NT from a passed hand (protective)Stretching with a good eleven-count and the usual transferred-king principle.
1NT from a passed hand (non-protective)5-5 shape and a distribution that can't be shown with either Unusual 2NT or Michaels, e.g. the black suits after a diamond opening. If there's no such unshowable distribution (i.e. after a major opening), it's the LOWER of the two Michaels options, i.e. (1S) passed-hand-1NT would show clubs+hearts.
1NT15-17, natural, with a useful holding in any opposition suits. Responses are the same as after a 1NT opening bid.
2C cue bidNatural club overcall. This remains true even if the opponents are playing a natural system and their 1C actually shows clubs. Our 2C overcall retains the same meaning irrespective of that.
2D over one of a minorMichaels, 5-5 in the majors
2NT5-5 in the lowest two unbid suits, Unusual 2NT
Jump to 3-level cue bidasking partner to bid 3NT if they have a stopper in this suit
Jump to 3NTTo play, long running minor.
4NTAcol 4NT, asking for specific aces
5NTasking for specific kings
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Copyright 2015 Finn Clark.