Negligence
The legal theory that someone failed to exercise reasonable care, causing harm — the basis of most personal injury claims.
Negligence is a civil tort (not a crime) requiring proof of four elements: (1) duty — the defendant owed the plaintiff a legal duty of care; (2) breach — the defendant failed to meet that standard; (3) causation — the breach caused the plaintiff's injury (both actual cause and proximate cause); and (4) damages — the plaintiff suffered measurable harm. All four elements must be proven; failure on any one defeats the claim.
The standard of care is what a "reasonable person" would do in the same circumstances. Professionals (doctors, lawyers, accountants) are held to the standard of their profession — what a reasonably competent professional in that specialty would have done. This higher standard is what underlies malpractice claims.
Defenses to negligence include: contributory negligence (plaintiff's own negligence bars all recovery in a few states), comparative negligence (plaintiff's recovery is reduced by their percentage of fault — the rule in most states), assumption of risk (plaintiff voluntarily undertook a known risk), and statute of limitations. In comparative negligence states, if a plaintiff is 30% at fault, they recover only 70% of their damages.
Real-World Example
The store employee mopped the floor but failed to place a "wet floor" sign; when the customer slipped and broke her wrist, the jury found the store 80% negligent and the customer 20% negligent for wearing flip-flops, awarding $40,000 (80% of the $50,000 in damages).