in law, the failure to meet a standard of behaviour established to protect society against unreasonable risk. Negligence is the cornerstone of tort liability and a key factor in most personal injury and property-damage trials.

The doctrine of negligence originally applied to “public” professionals, such as innkeepers, blacksmiths, and surgeons, but it was probably prompted by industrialization and increased occupational accidents. At first, liability was harsh, but then it was softened to encourage industrial growth. The later trend is toward greater liability.

The doctrine of negligence does not require the elimination of all risk from a persons' conduct—only all unreasonable risk, which is measured by the seriousness of possible consequences. Thus, a higher standard applies to nitroglycerin manufacturers than to those making kitchen matches. In certain critical fields—e.g., the milk industry—the law imposes liability for any mistakes, even when the strictest precautions are taken, a policy known as strict liability.

The standard of behaviour is external. Generally the law examines only conduct, not the excitability, ignorance, or stupidity that may cause it. The courts determine what the hypothetical “reasonable man” would have done in the situation. Such standards also demand a degree of foresight in anticipating the negligence of others—especially of special groups such as children.

The reasonable-man test presumes certain knowledge—e.g., that fire burns, water may cause drowning, and cars may skid on wet pavement. Community custom will influence such presumptions, such as the practice of driving on a certain side of the road even on private roads, a situation in which laws do not apply. Emergencies, however, can soften the application of such standards.

Allowances may be made for physical (but not mental) handicaps, such as blindness, but the law demands that handicapped persons avoid needlessly placing themselves in situations in which their inability may cause harm. Other than distinguishing between children and adults, the doctrine of negligence does not usually consider factors of age or experience.

Ordinarily the plaintiff in a negligence suit must prove the defendant's negligence by a preponderance of the evidence, which may be circumstantial so long as it is not too speculative. In some situations, once the plaintiff has established an apparent connection between his injury and the defendant's apparent negligence, the latter must disprove that connection. This is the doctrine of res ipsa loquitur (Latin: “the matter speaks for itself”). Generally the damages recoverable for negligence are a monetary compensation for injuries or losses that are deemed to have flowed “naturally and proximately” from the negligent act. See also contributory negligence.