The reasonable man or reasonable person standard is a legal fiction that originated in the development of the common law. The reasonable person is a hypothetical individual whose view of things is consulted in the process of making decisions of law. The question, "How would a reasonable person act under the circumstances" performs a critical role in legal reasoning in areas such as negligence and contract law.

Table of contents
1 Rationale behind the standard
2 Professional negligence: the reasonable doctor
3 Reasonable bystander
4 Some critical approaches to the reasonable person standard

Rationale behind the standard

The rationale for such a standard, is that the law will benefit the general public when it serves its reasonable members, and thus a reasonable application of the law is sought, compatible with planning, working, or getting along with others. The reasonable man is not the average man: this is not a democratic measure. To predict the appropriate sense of responsibility and other standards of the reasonable man, "what is reasonable" has to be appropriate to the issue. What the "average man" thinks or might do is irrelevant to a case concerning medicine, for example. But the reasonable person is appropriately informed, capable, aware of the law, and fair-minded. She might do something extraordinary under certain circumstances, but whatever he or she does or thinks is always reasonable.

Professional negligence: the reasonable doctor

In cases where professional opinions may be necessary the doctrine of the reasonable professional has developed. Thus if a doctor misdiagnoses a patient, the question is not, "Was that diagnosis wrong?" but rather, "Would a professional acting under the same circumstances, with the knowledge available to the field at the time of the diagnosis, have concluded that the given diagnosis was reasonable?" Questions about the knowledge of a professional in a particular discipline in a particular environment are relevant here, "Is the reasonable professional an expert or a general practitioner in this area? Of course as with any legal concept these lines of reasoning may be applied differently in differing jurisdictions.

Reasonable bystander

A related notion, used in common law contract law, is that of a reasonable bystander or reasonable third party. It is also known as the objective theory of contract formation and it is distinguished from the subjective theory of contract formation that is accepted in most civil law jurisdictions. Sometimes, particularly in the context of verbal contracts, the existence of a contract is disputed because one party declares that he or she did not intend to be legally bound. Since it would be impractical for the court to try to determine the truth of this statement, it uses the following test instead: if the outward conduct of the parties would have indicated to a reasonable bystander a serious intention to enter into an agreement, then the contract is deemed legally binding. Another circumstance where the reasonable bystander is used occurs when one party has inadvertently misstated the terms of the contract, and the other party sues to enforce those terms: if it would have been clear to a reasonable bystander that a mistake had been made, then the contract is voidable by the party who made the error; otherwise, the contract is binding.

Some critical approaches to the reasonable person standard

The reasonable man standard has been criticized as being sexist by various feminist and critical legal studies theorists. This has led to the adoption of the reasonable person nomenclature in some jurisdictions. However, the rejoinder might be that, a change in jargon does not alter the reality that, the reasonable person standard is a tradition dominated by the perspectives of elderly, male lawyers: for critics, the "reasonable person" bears suspicious resemblance to an Establishment "fat cat". After all, the "reasonable person" is not an ideologue or extremist of any kind: she solidly represents the ideal citizen, and thus there is no "reasonable Marxist" or "reasonable Fascist", which is frustrating to those who are ideologically inspired.

Advocates of the reasonable man standard defend it as an exercise in pretended objectivity. The jurist or legislator pretends to see through another's eyes, and in light of the characteristics of a given situation tries to subtract every petty human trait and unrealistic expectation, as a balancing test: Is the transaction cost of proposed conduct worth it in the hypothetical situation? The problem, critics argue, is that this leaves no room for a heroic use of law; how can there be limits on efforts to prevent the negligent loss of life or limb, prejudiced in favor of a cold, economic calculus of loss, to determine when human life is "worth it"?

See also: torts, contract theory, casuistry