Negligence per se lets a plaintiff use a defendant's violation of a statute or regulation to establish the breach element of a negligence claim, rather than having to prove that the defendant fell below the general reasonable-person standard. The legislature has already fixed the standard of care; the violation is the breach.

The doctrine streamlines proof. Instead of arguing what a reasonable person would have done, the plaintiff points to a concrete legal rule the defendant broke. But it only applies when the statute was designed to protect this kind of plaintiff against this kind of harm.

Two gateway conditions are essential: (1) the plaintiff must be a member of the class of persons the statute was intended to protect; and (2) the harm suffered must be of the type the statute was designed to prevent. If either fails, the statutory violation does not establish negligence per se.

When both are met, most jurisdictions treat an unexcused violation as conclusively establishing breach; the plaintiff still must independently prove duty (often supplied by the statute), causation, and damages. A minority treat the violation only as evidence of negligence.

Negligence per se establishes breach, not the whole case. The plaintiff must still show the statutory violation was both the cause-in-fact and the proximate cause of the injury. A defendant can violate a statute yet avoid liability if the violation did not actually cause the harm.

This is why defendants often concede the violation but contest causation: the broken rule may be legally irrelevant if the same injury would have happened anyway, or if some other force was the real cause.

Courts recognize legally cognizable excuses for a violation -- for example, an emergency not of the defendant's own making, incapacity, or a reasonable but unsuccessful attempt at compliance. A validly excused violation does not establish negligence per se.

Defenses also attack the threshold: arguing the plaintiff is outside the protected class, the harm is outside the statute's purpose, or the statute is the kind of administrative or licensing rule courts decline to use as a liability standard. Causation and comparative fault remain available as in any negligence case.

Negligence per se is a powerful simplifier: it can turn a contested reasonableness question into a documented rule violation, strengthening summary-judgment and trial posture on the breach element. Plaintiffs often plead it alongside ordinary negligence so a jury can find liability either way.

As a claim path, it replaces the fuzzy 'reasonable care' node with a cleaner 'statutory violation' node gated by the protected-class and harm-type conditions, while causation remains a live downstream branch. In Juricratic you can dial the fit between statute and injury and the strength of any excuse, then watch how the modeled breach path firms up or collapses. The dials are exploratory, not predictions of the ruling.