Contributory negligence is a common law tort rule (created by judges in court opinions, judicial decisions, or case law) that bars or prevents a plaintiff from recovering on a claim for negligence if the plaintiff contributed to the cause of the accident (was contributorily negligent) in any way. This rule may be referred to as pure comparative negligence.

Some states still apply the contributory negligence rule. But because of the harsh outcome of the contributory negligence rule, many state legislatures have enacted statutes that provide for comparative negligence or fault and reduce the plaintiff’s recovery by the amount of the plaintiff’s negligence or fault. This rule may be referred to as pure comparative fault.

Other states have enacted a modified comparative fault statute or law that reduces a plaintiff’s recovery by the plaintiff’s percentage of fault, but bars a plaintiff from any recovery if the plaintiff is 50% or more at fault for the cause of the accident.

And in South Dakota, the comparative fault system uses a slight/gross negligence system and only analyzes the comparative fault if the plaintiff’s negligence is slight and the defendant’s negligence is gross. Under this slight/gross negligence system, if the plaintiff’s negligence is more than slight and the defendant’s negligence is less than gross, the plaintiff is barred or prohibited from any recovery.

These contributory negligence and comparative fault laws vary from state to state and may change or evolve at any time—whether they are located in court opinions or in statutes.

In Massachusetts, the rule of contributory negligence has been replaced by a modified comparative negligence system. Under Massachusetts General Laws Chapter 231, Section 85, a plaintiff's recovery is reduced by their percentage of fault. However, if the plaintiff's negligence is found to be 50% or more responsible for the accident, they are barred from recovering any damages. This means that as long as the plaintiff is found to be less than 50% at fault, they can still recover damages, but the amount will be reduced in proportion to their degree of fault. This approach is intended to allocate damages more fairly than the traditional contributory negligence rule, which would prevent any recovery if the plaintiff was found to be at all responsible for the accident.