Contributory negligence folds in all the elements of a negligence case against the plaintiff, with the plaintiff as his or her own victim. Traditionally, any amount of negligence by the plaintiff extinguished the case against the defendant. The harshness of that rule led to some countervailing exceptions to flip the “all” of the defense back to “nothing” — exceptions like the last clear chance doctrine, by which the plaintiff’s negligence wouldn’t count against the case if the plaintiff’s poor behavior had made him helpless, and then the defendant, seeing that, acted negligently anyway. Starting in the 60’s and 70’s, American tort law started to split the difference between all or nothing. The concept of comparative negligence was introduced, and juries might be asked to compare the defendant’s negligence against the plaintiff’s, deducting the plaintiff’s share from any recovery. How to make such comparisons is far from clear, especially in cases with multiple defendants, each playing very different roles.