Contributory negligence is an affirmative defense and often a mirror image of the claim of negligence against the defendant. To establish contributory negligence, a defendant generally has to meet all four elements of negligence (duty, breach, causation, damages) in the same way the plaintiff does. Until recently, contributory negligence functioned as a total bar on recovery.
In practice, however, the rule may have been less harsh because juries could decide the plaintiff wasn’t at fault if the defendant appeared to be more at fault (this is a form of jury nullification), and because courts developed ameliorative doctrines such as the “last clear chance rule,” which maintains that even though the plaintiff was contributorily negligent, the defendant had the last clear chance to avoid the injury and thus the plaintiff still recovers. Few states have retained contributory negligence as an absolute bar. Most have moved to comparative responsibility. Once states have made that move, doctrines such as the “last clear chance” become unnecessary.
Once the old contributory negligence regime has been thrown out, what fills the void? The answer, in short, is comparative responsibility. To move from contributory negligence to comparative responsibility is to reject the rule that a plaintiff is barred from recovery if he, too, was careless. Under a comparative responsibility system, the responsibility is split evenly among the parties who were at fault.