From the fact that the call has been passed, the dealer's partner must credit the dealer with less than average strength as regards the rank of his cards, and probably a slightly increased number of black cards; he must therefore be more backward in making a high declaration whenever he can make a sound declaration of less value. On the other hand, he has not the option of passing the declaration, and may be driven to declare on less strength because the only alternative is a short suit of spades. For example, with the hand: Hearts, ace, kv. 2; diamonds, qn. 9, 7, 6, 3; clubs, kg. 10, 4; spades, 9, 2, the chances are in the dealer's favour with five trumps, but decidedly against with only two, and the diamond declaration is to be preferred to the spade. Still, a hand may be so weak that spades should be declared with two or less, but five clubs or six diamonds would be preferable with the weakest of hands.
When one's score is over twenty, club declarations should be made more frequently by the dealer. Spades should be declared with six at the score of twenty-six and with five at twenty-eight. When much behind in the score a risky no-trumper such as one with an established suit of seven or eight cards without a card of entry, may be declared.
Declaring to the score is often overdone; an ordinary weak no-trump declaration carries with it small chances of three by tricks unless dummy holds a no-trump hand.
Practically the leader only doubles a no-trump declaration when he holds what is probably an established suit of seven cards or a suit which can be established with the loss of one trick and he has good cards of re-entry. Seven cards of a suit including the ace, king and queen make sound double without any other card of value in the hand, or six cards including king, queen and knave with two aces in other suits.
Doubling by the third hand is universally understood to mean that the player has a very strong suit which he can establish. 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.