The reasonable person (formerly, the "reasonable man") is a concept developed in the law of negligence that is also used in certain situations regarding intellectual property, trusts, sexual harassment and contract. The existence of such a person is considered to be a useful legal fiction and frames the level of the duty of care required when negligence is alleged.
The standard does not require a person to act to the highest possible level of care in the circumstances, but it requires an individual to act with more than good faith. It is somewhat similar to the concept of due diligence in that a party is expected to act as another reasonable person in the same circumstances would.
Although the concept was developed in common law, it has since been incorporated into many jurisdictions with a civil code (French: personne raisonnable) replacing the old standard of pater familias.