For you thus weaken him, and leave it in the power of the antagonists to draw all the trumps, and bring in their suit. If, then, a good partner refrains from forcing you, you may be sure he is weak; on the other hand, if he evidentlyintendsto force you (as by leading a losing card of a suit he knows you must trump), you may assume that he is strong in trumps, and you should take the force willingly, even though you do not want to be forced, depending on his strength to exhaust the adversaries' trumps.
You may, however, though weak, force your partner under these circumstances. 1. When he has already shown a desire to be forced, or weakness in trumps, as by trumping a doubtful card, or by refraining from forcing you. 2. When you have a cross-ruff, which secures several tricks at once, and is therefore often more advantageous than trying to establish a suit. 3. Sometimes when you are playing a close game, as for the odd trick, and often when one trick saves or wins the game or a point. And 4. Sometimeswhen great strength in trumps has been declared against you.
If your partner leads a thirteenth card, or a card of a suit in which he knows that both you and the fourth player renounce, your play must depend on your partner's strength in trumps. If he is strong, he wants you to put on your best trump, either to make the trumps separately, or to force out one or two high ones, to leave himself with the command. If he is weak in trumps, he wants you to pass the card, that the fourth player may obtain the lead, and lead up to your hand. No general rule can be given as to the course to be pursued with regard to thirteenth cards. You must judge of the leader's intention by the score and the previous fall of the cards.