---
title: "Reasonable Person Standard"
type: Legal Rule
source: https://casebriefly.com/legal-rules/reasonable-person-standard
---

# Reasonable Person Standard

The objective standard by which a defendant's conduct is measured in negligence cases. A person must act as a reasonably prudent person would under the same or similar circumstances.

## Definition

The reasonable person standard is the benchmark used to determine whether a defendant has breached a duty of care. It is an objective standard: the question is not what the particular defendant thought was appropriate, but what a hypothetical person of ordinary prudence would have done under the same or similar circumstances. This standard applies regardless of the individual defendant's subjective good intentions or personal limitations.

The standard originated in the English common law and was articulated in Vaughan v. Menlove, where the court rejected a subjective standard based on the defendant's best judgment. The reasonable person is sometimes described as a person of ordinary intelligence and prudence. Importantly, the standard is flexible — it accounts for the circumstances, including the likelihood and severity of harm, the burden of precaution, and the social utility of the defendant's conduct, as captured by the Hand Formula from United States v. Carroll Towing Co.

Certain modifications to the standard exist. Children are held to the standard of a reasonable child of similar age, intelligence, and experience (except when engaged in adult activities). Individuals with physical disabilities are held to the standard of a reasonable person with that same disability. However, mental disabilities and below-average intelligence generally do not lower the standard. Professionals (doctors, lawyers, architects) are held to the standard of a reasonable professional in that field. The reasonable person standard serves as the bridge between duty and breach.

## Elements

- Objective standard — not based on the defendant's subjective beliefs or abilities
- Measured by what a person of ordinary prudence would do under the same circumstances
- Accounts for external circumstances such as emergencies and environmental conditions
- Modified for children (reasonable child standard, except in adult activities)
- Modified for professionals (standard of a reasonable practitioner in that specialty)
- Physical disabilities are incorporated, but mental disabilities generally are not

## Key Case

Vaughan v. Menlove, 132 Eng. Rep. 490 (1837)

## Landmark Cases

| Name | Citation | Significance |
| --- | --- | --- |
| Vaughan v. Menlove | 132 Eng. Rep. 490 (1837) | Rejected the subjective standard of individual judgment in favor of the objective reasonable person standard. |
| United States v. Carroll Towing Co. | 159 F.2d 169 (2d Cir. 1947) | Judge Learned Hand articulated the B < PL formula for determining whether conduct is reasonable, balancing burden of precaution against probability and magnitude of harm. |
| Bethel v. New York City Transit Authority | 92 N.Y.2d 348 (1998) | Abolished the higher standard of care for common carriers, applying the ordinary reasonable person standard universally. |
| Robinson v. Lindsay | 92 Wash.2d 410 (1979) | Held that children engaged in adult activities (such as operating motorized vehicles) are held to an adult reasonable person standard. |

## Exam Tips

- Apply the Hand Formula (B < PL) when analyzing whether conduct was reasonable — compare the burden of precaution to the probability and gravity of harm.
- Always note modifications to the standard when the defendant is a child, a professional, or has a physical disability.
- Do not confuse the reasonable person standard with perfection — the standard requires reasonable care, not the elimination of all risk.

## Common Mistakes

- Applying a subjective standard based on what the defendant believed was reasonable rather than the objective standard of a reasonable person.
- Forgetting that mental illness or below-average intelligence does not reduce the standard of care owed.
- Failing to apply the professional standard when the defendant is a doctor, lawyer, or other specialist.

## Mnemonic Or Memory Aid

The Hand Formula: B < PL means Breach. If the Burden of precaution is less than the Probability times the Loss, the defendant was unreasonable.

## Related Rules

- duty-of-care-general
- comparative-negligence
- contributory-negligence
- negligent-infliction-of-emotional-distress

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Source: [Reasonable Person Standard — CaseBriefly](https://casebriefly.com/legal-rules/reasonable-person-standard)