When discussing a personal injury accident case in Pennsylvania, one may hear the person who allegedly caused the accident or injury referred to as "negligent." It's one thing to be negligent in a day-to-day sense, like forgetting to stop at the store for milk. But demonstrating negligence in a legal sense - with respect to a car accident, for example - requires much more than proof of absent-mindedness.
A plaintiff - the injured party - must demonstrate five things before a defendant (the alleged wrong-doer) will be considered negligent. First of all, the plaintiff must show that the defendant owed a duty. Using the car accident example, the defendant may have a duty to obey traffic laws and drive safely in light of current road conditions. Secondly, the plaintiff must show that the defendant acted in a way that breached that duty, say by driving drunk.
Next, the plaintiff must prove that the defendant's breach of duty was a direct cause of the accident. This is often demonstrated by a "but-for" test: But for the defendant's drunk driving, the accident would not have happened. The penultimate element of negligence is proximate cause, which hinges on foreseeability. Was it reasonably foreseeable that drinking too much and getting behind the wheel of a car would cause an accident?
Lastly, the plaintiff must show that the the defendant's actions caused the plaintiff to suffer damages. Damages, in a legal sense, can be anything from a dented bumper to pain and suffering. As long as damages can be proven, and all the other elements have been demonstrated, a defendant may be found legally negligent. And if they are legally negligent, the defendant can be held liable for the damages suffered by the plaintiff.
Source: FindLaw.com, "Elements of a negligence case," accessed Apr. 14, 2018