The 'but for' method, also known as 'sine qua non,' is a simple and usually reliable method of establishing cause and effect. In this method, the court determines whether harm or injury would have occurred if the defendant had not been involved in the incident. If a court finds that the harm (effect) would have occurred even without the defendant being present, then it is probable that he is not the cause of the harm. On the contrary, if the harm (effect) would not have happened 'but for' the defendant causing it to occur, then the defendant could be found liable for this effect.
"Legal causation," also known as the "proximate cause" method, seeks to establish the cause that led to an injury as a result of an uninterrupted chain of events. Without this direct and uninterrupted chain of events, the victim would not have suffered the effects. For there to be legal or proximate cause, the chain of events that led to that harm must not be broken by unforeseeable acts such as natural disasters like an earthquake. Unforeseeable acts include: unpredictable acts by the victim that resulted in the injury, natural events or the uniformed acts of a third party, other than the defendant.
This method is used to establish which act among many undertaken by a defendant was, in fact, the sole cause of the harm rendered to the victim. This method is often used in criminal litigation whereby more than one cause could have resulted in a single effect or harm. The court uses this method to eliminate all the possible causes of harm and to arrive at the substantial cause of the harm. For example if person Z starts a fire on one side of person C's house and person B starts another fire on the other side of C's house and the fires converge to burn down person C's house and kill him, too, the court must use the substantial factor method to establish whether Z or B bears the most criminal responsibility for burning down C's house and killing him.
The "foreseeability test" is one of the methods that is used in determining legal causation. In criminal litigation, the court seeks to determine whether the defendant had the capacity to foresee the effects that his actions would cause. If foreseeability of the effects is established, then the defendant could be held liable for his acts. The extent to which the harm was caused or the type of harm does not need to be foreseen. Therefore, if a defendant intended only to inflict minimal harm but, instead, the harm surpassed what he had foreseen, he might still bear criminal responsibility.