Correct contract bridge / by E.V. Shepard ; including the official Laws of contract bridge adopted by the Whist Club, New York, and by all the leading clubs in America.

IX
INFORMATORY DOUBLES
THERE are "informatory doubles" and "business doubles. The first ask partner to make his
best bid, unless he can defeat the doubled contract
for greater gain than can result from any responsive
bid; the second species of double asks partner to let
the doubled contract stand, unless he can go game
by bidding.
The informatory doubler assumes all responsibility for the result of his partner's answering bid.
Weakness is no excuse for failure to make a responsive declaration.
Too few informatory doubles are employed at
Contract; sometimes Contract games move too rapidly for an Auction brain to act logically, opponents
snapping into a bid of 2-odd or 3-odd, whereas an
Auction bid of only one might have been made. In
many instances Auction rules for making informatory doubles are insufficiently comprehensive to
cover Contract situations; players fail to make
doubles that would give partners enlightening clues
and opponents are allowed to get away with a contract not belonging to them. Don't let this occur.
If you have proper doubling values, double.
The requirements for a double to be informatory
are:
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