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INFERENCES AND DECUCTIONS
A deduction is a conclusion based upon known fact. ††For example, when a defender
shows out in a suit, declarer can count the holding in that suit in the hand of the partner who
exhibits the void.†† An inference is a conclusion based upon an assumed fact. ††For example, when an opponent passes his partner's opening one bid, you can infer that he/she has fewer than 6 HCP's.
Inferences and deductions about the opponents' high cards and distribution can both be made from the auction and the play of the hand.
A.† INFERENCES FROM THE AUCTION:
1. A player who has passed the opportunity of opening the bidding in first or second positions cannot have 13 HCP's, for, indeed, all 13 HCP hands satisfy the Rule of 20 and would have opened the bidding†† Therefore, if such a passed hand has already evidenced 2 Aces and
††††† 1 King, in the play of the hand, he/she cannot hold a missing King or Queen.
2.† A player who passes in response to his/her partner's opening hand cannot have 6 HCP's.†† If†††
†††† he/she has, in the play of the hand, already evidence a King and a Jack, he/she cannot have†
†††† a Queen for which you might like to finesse against.
3.† An opening 1NT bidder has the HCP's defined by his opening no trump stipulated
†††† range, usually 15-17 HCPís.
4.† A responder who has bid 1NT in response to his/her partnerís opening one Heart, holds 6‑10 HCP's, no 4‑card Spade Major holding, and lacks primary support for his/her partner's Heart suit.
5.† A 1NT (2NT) opening bidder who responds "2D" ("3D") to his partner's "2C" ("3C") Conventional Stayman bid lacks a 4‑card suit in either Major suit.
6.† The partner of an opening 1 NT bidder who receives a 2S bid from his/her partner in response to a "2C" Stayman conventional bid, and who then bids 3NT had a 4‑card Heart suit, otherwise he/she would have never sought a Major suit fit.
7.† A responder who has bid a new suit at the 1‑level has at least 6 HCP's.
8.† A responder who has bid a new suit at the 2‑level has at least 10 HCP's.
9.† An player who makes an overcall has at least 5‑cards in his/her bid suit, in addition to 8 or more HCP's at the l-level, and 10 or more HCP's at the 2‑level.
10 An opening no trump bidder does not have a singleton, a void, a 5-card Major suit holding,††
†††† nor a 6‑card suit.
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11 A responder who raises a Minor does not have a 4‑card Major suit holding.
12 A opening weak two‑bid probably evidences a 6‑card suit, and a three‑bid a 7‑card suit.
13 An opening bidder of 1H or 1S has at least a 5‑card or longer Major suit holding.
14 If the opponents have opened and raised a Major suit and you have 5 cards in that suit, your partner has a void in that suit.
15. †A responder who responds 1S to a 1C or 1D opening bid by partner does not likely have a 4-card Heart suit.
16. †An opening bid of 1C or 1D probably denies a 5-card Major suit holding.
B.† INFERENCES FROM THE PLAY:
1.† If the opening leader against a no trump contract leads a deuce, then he/she does not have a 5‑card suit, since he has, by partnership and conventional understanding, led fourth from his/her longest suit.
2.† lf the opening leader leads a low card, he/she does not have an honor sequence in that suit, again, by partnership and conventional understanding.
3.† If the opening leader leads a low card, he/she either has a singleton, or else three, or more cards in that suit headed by an honor.
4.† If, as declarer, you are missing the ace and the king in any suit, and the opening leader does not lead that suit, he/she does not have both the ace and king.
5.† If the partner of the opening leader has bid a suit and the opening leader does not lead the suit bid by his/her partner, he/she probably has a good reason for not doing so.† The most common reasons are: (a) that he/she has an honor sequence in some other suit that appears more likely to be fruitful (apparent from the opening lead), (b) that he/she has the ace of the bid suit or (c) he/she is void in that suit, or (d) does not listen to the bidding and/or wants to frustrate his/her partner.
†††††† Realize that the abundance of information available about high cards and distribution of the opponents' hands is voluminous.†† Additional inferences may be based upon attitude (low card = a "discouragement" or high card = a "come-on encouragement"), distributional signals like (High‑Low = an "even" or Low‑High = an "odd" number of cards in the signalled suit), the lead of low from an honor, the lead of top of a presumed sequence, and/or the line of play.†† Counting, deductive reasoning, and assumed inferences are all important tools towards better bridge and a confident, assured, and productive defense by the opponents; or a more successful offense by declarer.