Cover or Not rule is the most important defensive application. This rule help to make the right decision whether to cover or not the honor of the opponent played by the right side. The rule must be learned and defensive player who holds an honor in a suit which has an honor in dummy has to plan what to do prior to the play of this suit. In addition to the losses that is generated by not knowing this rule; not being prepared and pausing when an honor is played by the right side results in the information given to the opponent. The rule needs to be applied if there is chance of winning. There must be a chance of winning by an honor or a spot card in your or partner’s hand when rule is applied. The hope of this is sufficient; covering the opponent’s honor without any chance of winning will be a mistake, logic is always above all the rules. In spite of applying the rule depending on whether dummy is on the right or left, it gives the same result if the inspection is done with four hands open.