Arizona personal injury law has common principles, even though every case is different and each needs to evaluated separately. One of those principles is the idea of negligence, which has been defined simply as "conduct which falls below common standards established for the protection of others against unreasonable risk of harm". These standards of behavior exist in several ways. Common sense, common practice, common decency, and even by laws enacted by the Arizona legislature (called "statutes"). When one violates a standard of common sense or decency and injuries another, it may be considered "negligence". When one violates a statute (law) that is in place for the protection of others, it is called "negligence per se".

Negligence per se means that the person who violated the law is automatically deemed to be negligent. More formally, negligence per se applies if someone (1) violates a statute, and (2) causes harm to a person who was (3) within the group of people intended to be protected by the statute, and (4) the harm was the sort of harm the statute was created to prevent. If any one of these four (4) elements is absent, the person who violated the statute is not negligent per se, though they may still be negligent.

In nearly every Arizona personal injury case, it is necessary for an injured person (the plaintiff) to prove that the person responsible for their injuries (the defendant) acted unreasonably. If the plaintiff can establish the four elements of negligence per se, however, the law assumes that the defendant was negligent.

Example: Consider two hypothetical Arizona personal injury cases.

Case #1: A child is riding his bicycle along the sidewalk in a town that has a law which makes it illegal to ride on the sidewalk. The boy strikes a pole owned by the city that was in an unsafe place and suffers serious injuries to his knee. In this case, if the boy sues the city, he should expect the court to rule that he was negligent per se because he violated the town's regulation (element 1), caused harm (element 2), to a person who was meant to be protected by the statute, which in this case would include bicyclists because the idea of the regulation was that the sidewalks are safe only for foot traffic (element 3) and the bicycle crash was the sort of accident the rule was meant to prevent (element 4).

Case #2: A rental car agency rents a car to a driver whom the agency knows does not have a driver's license, in violation of a state statute. That driver later drives drunk and injures a third party. In a lawsuit by the third party against the rental agency, the court would probably rule that the agency was not negligent per se. Although they did violate the law (element 1) and, at least debatably, cause harm (element 2), it's unlikely the victim can prove elements 3 and 4. The purpose of the statute prohibiting renting a car to someone without a valid license was to keep unlicensed drivers off the road, not to ensure that people driving stayed sober behind the wheel. Of course, it might still be that the agency was unreasonable in renting a car to someone they knew had no license to drive, in which case the victim might prevail.

It is crucial to understand that under Arizona personal injury law, what constitutes "negligence per se' is very particular. It is important to have the guidance of an experienced Arizona personal injury lawyer, to assure that you get the compensation you deserve.