Comparative negligence apportions fault among the parties and reduces the plaintiff's damages by the plaintiff's own percentage of responsibility. It replaced the harsh common-law rule of contributory negligence, under which any fault by the plaintiff -- even one percent -- completely barred recovery.

Most U.S. jurisdictions now use some form of comparative fault, but the versions differ in a way that can decide a case. The threshold at which a plaintiff's fault cuts off recovery entirely is the single most important variable.

Under pure comparative negligence, a plaintiff can recover even if mostly at fault; damages are simply reduced by the plaintiff's percentage. A plaintiff 90 percent at fault still recovers 10 percent of the damages.

Under modified comparative negligence, recovery is barred once the plaintiff's fault crosses a threshold -- commonly either the '50 percent bar' (barred at 50 percent or more) or the '51 percent bar' (barred only when more than 50 percent at fault). A handful of jurisdictions retain pure contributory negligence, where any plaintiff fault bars recovery.

The factfinder assigns percentages of responsibility to each party (and sometimes to non-parties) based on the relative culpability and causal contribution of each. The plaintiff's award is then multiplied by one minus the plaintiff's share.

Apportionment can extend to multiple defendants, interacting with joint-and-several-liability rules that determine whether each defendant pays only its share or can be liable for the whole. Those rules vary significantly by jurisdiction and materially affect collectability.

Defendants develop comparative-fault evidence throughout the case -- the plaintiff's own carelessness, failure to mitigate, or disregard of obvious dangers -- aiming to push the plaintiff's percentage as high as possible, ideally over a modified-comparative threshold that bars recovery entirely.

Plaintiffs work to minimize their assigned share, emphasizing the defendant's superior responsibility and reframing their own conduct as reasonable under the circumstances. Because the outcome is a percentage, comparative negligence often turns settlement into a negotiation over the likely split rather than a binary win-or-lose.

Comparative negligence converts liability from all-or-nothing into a continuous variable, which is why it is central to valuation. A case worth a large sum at zero plaintiff fault may be worth far less at 40 percent, and nothing at all past a modified-comparative bar.

This maps naturally onto Juricratic's dial-based model: the plaintiff's fault percentage is a continuous dial, and the jurisdiction's bar (pure, 50 percent, 51 percent, or contributory) is a rule setting. You can war-game how the modeled recovery and settlement range deform as you sweep the fault dial across the threshold. The percentages are exploratory inputs, not predicted verdicts.