In tort law, a duty of care is a legal obligation which is imposed on an individual requiring adherence to a standard of reasonable care while performing any acts that could foreseeably harm others. It is the first element that must be established to proceed with an action in negligence. The claimant must be able to show a duty of care imposed by law which the defendant has breached. In turn, breaching a duty may subject an individual to liability. The duty of care may be imposed by operation of law between individuals who have no current direct relationship (familial or contractual or otherwise) but eventually become related in some manner, as defined by common law (meaning case law).
Duty of care may be considered a formalization of the social contract, the implicit responsibilities held by individuals towards others within society. It is not a requirement that a duty of care be defined by law, though it will often develop through the jurisprudence of common law.
Development of the general duty of care.
At common law, duties were formerly limited to those with whom one was in privity one way or another, as exemplified by cases like Winterbottom v. Wright (1842). In the early 20th century, judges began to recognize that the cold realities of the Second Industrial Revolution (in which end users were frequently several parties removed from the original manufacturer) implied that enforcing the privity requirement against hapless consumers had harsh results in many product liability cases. The idea of a general duty of care that runs to all who could be foreseeably affected by one's conduct (accompanied by the demolishing of the privity barrier) first appeared in the judgment of William Brett (later Lord Esher), Master of the Rolls, in Heaven v Pender (1883). Although Brett's formulation was rejected by the rest of the court, similar formulations later appeared in the landmark U.S. case of MacPherson v. Buick Motor Co. (1916) and, in the UK, in Donoghue v Stevenson (1932). Both MacPherson and Donoghue were product liability cases, and both expressly acknowledged and cited Brett's analysis as their inspiration.
Scope.
Although the duty of care is easiest to understand in contexts like simple blunt trauma, it is important to understand that the duty can be still found in situations where plaintiffs and defendants may be separated by vast distances of space and time.
For instance, an engineer or construction company involved in erecting a building may be reasonably responsible to tenants inhabiting the building many years in the future. This point is illustrated by the decision of the South Carolina Supreme Court in Terlinde v. Neely, later cited by the Supreme Court of Canada in Winnipeg Condominium Corporation No. 36 v. Bird Construction Co. 1 S.C.R. 85:
The plaintiffs, being a member of the class for which the home was constructed, are entitled to a duty of care in construction commensurate with industry standards. In the light of the fact that the home was constructed as speculative, the home builder cannot reasonably argue he envisioned anything but a class of purchasers. By placing this product into the stream of commerce, the builder owes a duty of care to those who will use his product, so as to render him accountable for negligent workmanship.
Responsibility.
Although the idea of a general duty of care is now widely accepted, there are significant differences among the common law jurisdictions concerning the specific circumstances under which that duty of care exists. Obviously, courts cannot impose unlimited liability and hold everyone liable for everyone else's problems; as Justice Cardozo put it, to rule otherwise would be to expose defendants "to a liability in an indeterminate amount for an indeterminate time to an indeterminate class." There must be some reasonable limit to the duty of care; the problem is where to set that limit.