The cause of defense refers to the fact that the defendant puts forward against the plaintiff's claim to prove that the plaintiff's claim is not established or not fully established, that is, to reduce his own responsibility or not to assume responsibility. Some scholars call it exemption. In Taiwan Province Province, China, it is called illegal reason. In tort law, the cause of defense is put forward for the request of bearing civil liability. Therefore, the defense cause of tort law, also known as exemption cause or mitigation cause, is derived from the principle of imputation and the constitutive requirements of tort liability. Different imputation principles lead to different components of responsibility, so it is required that the specific defense reasons should be adapted to the imputation principles and components of responsibility. Correspondingly, the defense reasons of tort law are also different. In order to be effective, the defense must have the following two elements:

1. Confrontation elements refer to specific elements that can confront tort civil liability, so that the original tort liability cannot be established. If the defendant's claim is not antagonistic, it can only prove that it has understandable circumstances, but it is not enough to oppose the other party's request and cannot be a defense.

2. Objectivity. The defense must be an objective fact and must have occurred. It cannot be a defense to simply assume that some damage has not occurred or simply deny that the other party's claim does not exist.

Classification of defense. In China's tort law, the common defenses mainly include duty behavior, self-defense, emergency avoidance, victim's commitment, self-help behavior, victim's fault, third party's fault, force majeure and accident. For these defenses, some scholars divide them into two categories: legitimate reasons and external reasons. [2] Same as [1] No.76.

Page 77. Some scholars divide it into general defense and special defense. General defense means that although the defendant's behavior has caused damage to the plaintiff, the defendant's behavior is legitimate, such as self-defense, emergency avoidance, ex post facto authorization, self-help behavior and so on. Special defense means that the damage is not caused by the defendant's behavior, but by an external cause, such as accident, force majeure, the fault of the victim, the fault of the third party, etc.

Legal basis:

"Tort Liability Law" clearly stipulates the defense reasons, mainly aiming at the situation that the third chapter of "Tort Liability Law of People's Republic of China (PRC)" does not bear the responsibility and reduces the responsibility, namely

Article 26 If the infringer is also at fault for the occurrence of the damage, the liability of the infringer may be reduced.

Article 27 If the damage is intentionally caused by the victim, the actor shall not be liable.

Article 28 If the damage is caused by a third party, the third party shall bear the tort liability.

Article 29 If damage is caused to others due to force majeure, it shall not be liable. Where there are other provisions in the law, those provisions shall prevail.

Thirtieth damage caused by justifiable defense, shall not be liable. If justifiable defense exceeds the necessary limit and causes undue damage, the justifiable defender shall bear corresponding responsibilities.

Thirty-first damage caused by emergency avoidance, the person who caused the danger shall bear the responsibility. If the danger is caused by natural reasons, the emergency evader shall not bear the responsibility or give appropriate compensation. If the measures taken for emergency hedging are improper or exceed the necessary limits, causing undue damage, the emergency hedging person shall bear corresponding responsibilities.