In most judicial systems, tort law is the area of the law that addresses injuries to the person or to property. Within tort law, there are three different types of torts — intentional, strict liability, and negligent torts. Among other elements necessary to prove negligence, a plaintiff, or injured person, must prove causation. One rule that courts have developed in order to determine causation is the "but for rule." In essence, the court asks the question whether the plaintiff's injuries would have occurred "but for" the actions of the defendant.
Tort laws generally contemplate intentional, strict liability, and negligent torts. Intentional torts require the plaintiff to show that the defendant's actions were intentional, such as in the case of a battery. Strict liability torts are rare and require no mens rea, or state of mind, on the part of the defendant. In some jurisdictions, dog bite injuries when the dog in question was a breed known to be aggressive, such as a pit bull, are considered strict liability torts, meaning the defendant will be liable despite taking precautions to prevent injury. The majority of torts fall into the third category of negligent torts.
Negligence generally requires the plaintiff to prove four elements including: a duty of care owed by the defendant to the plaintiff, a breach of the duty of care, causation, and damages. The "but for rule" is used to determine whether the plaintiff has met his or her burden on the element of causation. Courts have developed the "but for rule" over the years due to the often complicated task of determining causation in many tort cases.
Although the cause of a plaintiff's injuries may be apparent in some cases, in others, it is not. Sometimes, for instance, there is more than one cause, while in others, there are intervening events that make causation difficult to determine. The "but for rule" is a tool that allows the court to separate additional causes or intervening acts and ask the question, "But for the actions of the defendant, would the plaintiff have been injured?" If the plaintiff would not have been injured "but for" the actions of the defendant, then the defendant has at least some liability for the plaintiff's injuries. The "but for rule" is not the only rule or tool used to determine causation in a negligent tort case; however, it is widely used as it can quickly exclude a defendant from liability in some cases.