Negligence is the legal term for carelessness that causes harm. In plain terms, it is failing to act with the level of care that a reasonable person would have used, and someone getting hurt as a result. It is the legal theory behind most personal injury cases, from car crashes to slip-and-falls to medical errors. To win a negligence case, the injured person has to prove four specific things, called the elements: duty, breach, causation, and damages. If any one of them is missing, the claim fails, no matter how sympathetic the injury.
This post walks through the four elements with examples, then explains the related rules that most often change the outcome: negligence per se, comparative and contributory negligence, and who has to prove what.
What are the four elements of negligence?
Negligence is not just bad luck or a bad result. It is a specific legal claim with four parts, and the injured person (the plaintiff) must establish all four to recover from the person being sued (the defendant). The four elements are duty, breach, causation, and damages.
Duty
The first element is duty, meaning a legal obligation to use reasonable care toward the plaintiff. The general standard is the reasonable person standard: you owe others the care that a reasonably careful person would use in the same situation.
Everyone owes a basic duty not to create unreasonable risks of harm to others. Driving a car carries a duty to drive carefully toward other drivers, passengers, and pedestrians. A store open to the public owes its customers a duty to keep the premises reasonably safe. Some relationships raise the standard: a doctor owes a patient the care of a reasonably competent doctor, which is a professional standard higher than the ordinary reasonable person. Whether a duty exists, and how high it is, is the starting point of every negligence case.
Breach
The second element is breach, which means the defendant failed to meet the duty. Breach is the careless act or failure to act itself: doing something a reasonably careful person would not do, or failing to do something a reasonably careful person would do.
Running a red light is a breach of the duty to drive carefully. Leaving a spill on a store floor for hours without cleaning it or warning customers is a breach of the duty to keep the premises safe. A surgeon leaving an instrument inside a patient is a breach of the professional standard of care. The question a jury asks is whether the defendant's conduct fell below what a reasonable person, or a reasonable professional, would have done in the circumstances.
Causation
The third element is causation, and it has two distinct parts. The plaintiff must prove both that the breach in fact caused the harm and that the harm was a foreseeable result of the breach.
The first part is actual cause, often tested by the "but-for" question: but for the defendant's careless act, would the injury have happened? If the injury would have occurred anyway, the breach did not cause it. The second part is proximate cause, which limits liability to harms that are a foreseeable consequence of the careless conduct, rather than freak results connected only by a bizarre chain of events. A driver who runs a red light and hits a pedestrian is the actual and proximate cause of the pedestrian's broken leg. If, by contrast, the collision set off a wildly unforeseeable chain of events, a court may find the later harm too remote to be the driver's legal responsibility. Causation is where many cases are won or lost, because it is not enough to show carelessness and an injury; the carelessness has to be what produced that injury.
Damages
The fourth element is damages, meaning the plaintiff suffered actual, legally recognized harm. Negligence is not actionable without harm. A driver who runs a red light but hits no one and damages nothing has been careless but has committed no negligence claim, because no one was harmed.
Damages include physical injury, the medical costs of treating it, lost wages and lost earning capacity, property damage, and non-economic harm such as pain and suffering. The plaintiff has to prove the harm and connect it to the breach. This element is also what the money in a successful case is meant to address: the law's goal is to compensate the injured person for the losses the negligence caused.
What is negligence per se?
Negligence per se is a shortcut for proving breach. It applies when the defendant violated a safety law or regulation that was designed to protect against exactly the kind of harm that occurred, to the kind of person the law was meant to protect.
When negligence per se applies, the violation of the statute establishes the breach element automatically, so the plaintiff does not have to separately argue that the conduct was unreasonable. For example, if a driver violates a speed-limit or drunk-driving statute and causes a collision, the statutory violation can establish breach as a matter of law, because traffic-safety laws exist to prevent that exact kind of injury. The plaintiff still has to prove the other elements, especially causation and damages. The exact effect of negligence per se varies by state; in many states it conclusively establishes breach, while in others it creates a presumption the defendant can try to rebut.
What is comparative negligence?
In real cases, the injured person is often partly at fault too. Comparative negligence is the rule that reduces a plaintiff's recovery in proportion to that plaintiff's own share of fault. The states divide into several approaches, and which one applies can dramatically change, or eliminate, a recovery.
Under pure comparative negligence, the plaintiff's damages are reduced by the percentage of fault assigned to the plaintiff, no matter how high. A plaintiff found 80 percent at fault can still recover 20 percent of the damages. Under modified comparative negligence, the plaintiff can recover a reduced amount only if the plaintiff's share of fault stays under a threshold, which is set at either 50 percent or 51 percent depending on the state. At or above that bar, the plaintiff recovers nothing. Most states use one of the modified comparative systems.
A small number of states still follow contributory negligence, the older and far harsher rule. Under pure contributory negligence, a plaintiff who is even one percent at fault is barred from recovering anything at all. Only a handful of jurisdictions still apply this rule, but in those places a small share of the plaintiff's own fault can defeat the entire claim, which makes the fault analysis especially important there. Because these rules differ so much from state to state, the same accident can produce very different outcomes depending on where it happened.
Who has the burden of proof in a negligence case?
In a negligence case, the plaintiff carries the burden of proof on all four elements. The plaintiff must prove duty, breach, causation, and damages by a preponderance of the evidence, which means more likely than not, or just over 50 percent. This is a lower standard than the "beyond a reasonable doubt" standard used in criminal cases, because a negligence case is civil and is about compensation rather than punishment.
When the defendant raises an affirmative defense, such as comparative or contributory negligence, the defendant generally bears the burden of proving that defense, including the plaintiff's share of fault. There is also a special doctrine, res ipsa loquitur (Latin for "the thing speaks for itself"), that can help a plaintiff prove breach by inference when an accident is of a kind that ordinarily does not happen without negligence and the instrument that caused it was in the defendant's control, such as a surgical sponge left inside a patient. Even then, the plaintiff still has to prove the rest of the case.
How the elements fit together
The four elements are best understood as a chain, not a checklist. Duty defines the obligation, breach is the failure to meet it, causation ties that failure to the harm, and damages are the harm the law will compensate. A case is only as strong as its weakest link, which is why defendants so often attack a single element, usually breach or causation, rather than the whole claim. The comparative and contributory rules then sit on top of that chain, adjusting or in some states erasing a recovery based on the plaintiff's own share of fault. Because the standard of care, the effect of a statutory violation, and the fault rules all vary by state, the same facts can lead to different results in different courtrooms, which is why the specific law of the state where the injury happened always matters.