You may see it in a claim letter, police report, insurance denial, or a lawyer's explanation: one side is alleging that someone "failed to use reasonable care" and caused harm. That is what negligence means. It is the failure to act with the level of caution a reasonably careful person would use under the same circumstances. A driver who speeds into a whiteout on the Thruway, a property owner who ignores a dangerous condition, or a city that leaves a known road hazard unaddressed may all be accused of negligence if that carelessness leads to an injury.

In a personal injury case, negligence is often the foundation of liability. To prove it, the injured person usually has to show four things: a duty of care existed, that duty was breached, the breach caused the injury, and actual damages resulted. Evidence can include photos, witness statements, medical records, repair records, and notice of the hazard. In New York, that can matter in cases involving potholes tracked through the city's 311 system or crashes during lake-effect snow on I-90 or I-87.

Negligence also affects how much money may be recovered. Under New York's pure comparative negligence rule, CPLR § 1411, a person's damages can be reduced by their own share of fault, but not wiped out completely just because they were partly to blame. That makes negligence a key issue in settlement talks and trial.