In response to the
double his partner, according to different conventions, leads either a
heart or his own shortest suit as the one most likely to be the third
player's strongest. Under the short suit convention, if the doubler holds
six of a suit headed by the ace, king and queen, it is about an even chance
that his suit will be selected; he should not double with less strength.
Under the heart convention it is not necessary to have such great strength;
with a strong suit of six hearts and good cards of re-entry, enough tricks
will be saved to compensate for the doubled value. A player should
ascertain the convention followed before beginning to play.

Before doubling a suit declaration a player should feel almost certain that
he is as strong as the declarer. The minimum strength to justify the
declaration is generally five trumps, but it may have been made on six. If,
then, a player holds six trumps with an average hand as regards the rank of
his cards, or five trumps with a hand of no-trump strength, it is highly
probable that he is as strong as the declarer. It must be further taken
into account that the act of doubling gives much valuable information to
the dealer, who would otherwise play with the expectation of finding the
trumps evenly distributed; this is counterbalanced when the doubler is on
the left of the declaring hand by the intimation given to his partner to
lead trumps through the strong hand. In this position, then, the player
should double with the strength stated above. When on the declarer's right,
the player should hold much greater strength unless his hand is free from
tenaces. When a spade declaration has been made by dummy, one trump less is
necessary and the doubler need not be on the declarer's left. A spade
declaration by the dealer can be doubled with even less strength. A
declaration can be rather more freely doubled when a single trick undoubled
will take the dealer out, but even in this position the player must be
cautious of informing the dealer that there is a strong hand against him.

_Redoubling._--When a declaration has been doubled, the declarer knows the
minimum that he will find against him; he must be prepared to find
occasionally strength against him considerably exceeding this minimum.
Except in the case of a spade declaration, cases in which redoubling is
justifiable are very rare.

_The Play of the Hand._--In a no-trump declaration the main object is to
bring in a long suit