Introduction
Today’s Legal Theory Lexicon is about the “reasonable person.”
The notion of a “reasonable person” usually makes its first appearance in the Torts course. The context, of course, is the tort of negligence, where the “reasonable person” is used to define the standard of care that triggers liability for unintentional harms. But what makes a “reasonable person” reasonable? The concept of the reasonable person is not limited to torts, however. The reasonable person makes appearances in criminal law, contract law, and elsewhere. As usual, the Legal Theory Lexicon introduces the “reasonable person” for the law student with an interest in legal theory.
A cautionary note. The word “reasonable” is used in a wide variety of legal contexts, some of which have very little to do with the reasonable person. In antitrust law, for example, the notion of “an unreasonable restraint of trade” is crucially important, but this topic does not, at least on the surface, have anything to do with the reasonable person of torts and criminal law.
The Reasonable and the Rational
This is, after all, the Legal Theory Lexicon, so I hope you will forgive me for starting at a fairly high level of abstraction. “Reasonable” and “rational” are used in many different contexts and have a variety of meanings, but when I think about the “reasonable,” the first thing that comes to mind is the distinction between the reasonable and the rational that was articulated by W.M. Sibley in a 1953 article but was made famous by John Rawls.
When the rational is defined in contradistinction to the reasonable, rational usually refers to instrumental rationality—that is, the rationality of ends and means. Given that an agent has end X, it is rational for the agent to engage in action Y, only if Y will lead to X. Instrumental rationality is relative to the ends of a particular agent, and may (but need not) consider the interests of others. Thus, it may be instrumentally rational for me to steal from you, if you have something that I want and I have good reason to believe that I won’t get caught. But it may also be rational for me to help a stranger, if I happen to have the welfare of others as my end.
When we contrast the reasonable with the rational, the notion of the reasonable goes beyond instrumental rationality. It may be rational for me to steal from you, but unreasonable for me to do so. Why? Well, that is quite a question. One answer is based on the idea that the reasonable is, in some way, connected to what could be justified to others. Another idea is that the reasonable is in some way specified by that to which others would consent.
So as we are thinking about the “reasonable person,” it is important to distinguish her from her cousin, the “rational person.” The rational person may or may not take the interests of others into account. To be a reasonable person, however, is to consider the interests or viewpoints of others—to give them their proper due.
Of course, all of this is terribly vague! What does it mean “to give the interests of others their proper due”? How much is enough? How much is too much? So far, we have only the general concept of the reasonable person. In order to make use of the “reasonable person” in the law, we need a particular conception of the “reasonable person”—a set of standards or criteria that will enable us to sort the reasonable actions from the unreasonable ones.
Subjective and Objective Reasonableness
One more preliminary distinction—much is made of the difference between subjective and objective reasonableness. We might, for example, distinguish between the “reasonable person” and the “reasonable intoxicated person” or the “reasonable person with a developmental disability” or the “reasonable person with a hot temper.” Usually, we call the reasonable-person standard an objective standard, signifying that we are not taking the particular characteristics of defendants in tort or criminal actions into account when we ask whether they met the relevant standard of care.
The reasonable “person” used to be the reasonable “man.” For most of the history of negligence law, the standard was stated in just those terms. Vaughan v. Menlove, decided in 1837, asked whether the defendant had shown the caution that “a man of ordinary prudence” would observe, and English judges later personified the standard as the man on the Clapham omnibus. The Restatement (Second) of Torts, published in 1965, still asked what “a reasonable man under like circumstances” would do. American courts shifted to “reasonable person” over the following decades, and the Restatement (Third) of Torts, completed in 2010, uses the person formulation throughout. Is the change merely cosmetic, a matter of updating the pronouns? Not everyone thinks so.
Some critics of the reasonable person standard argue that its “objectivity” is a mask for a bias that favors some groups over others. On this, see Mayo Moran’s Rethinking the Reasonable Person: An Egalitarian Reconstruction of the Objective Standard.
Learned Hand and the Reasonable Person as Cost-Benefit Analyst
The conception of reasonableness that is most familiar to contemporary law students was introduced by Judge Learned Hand in the famous Carroll Towing case.
[T]he owner’s duty, as in other similar situations, to provide against resulting injuries is a function of three variables: (1) The probability that she will break away; (2) the gravity of the resulting injury, if she does; (3) the burden of adequate precautions. Possibly it serves to bring this notion into relief to state it in algebraic terms: if the probability be called P; the injury, L; and the burden, B; liability depends upon whether B is less than L multiplied by P: i.e., whether B < PL.
United States v. Carroll Towing Co., 159 F.2d 169, 173, reh’g denied, 160 F.2d 482 (2d Cir. 1947); see also The T.J. Hooper, 60 F.2d 737, 740 (2d Cir. 1932).
Hand offered the formula almost in passing, in an admiralty case about a barge that broke loose from its moorings, but it has since worked its way into the black letter. Section 3 of the Restatement (Third) of Torts, completed in 2010, defines a failure of reasonable care by reference to the same three factors: the foreseeable likelihood that the conduct will cause harm, the foreseeable severity of that harm, and the burden of the precautions that would eliminate or reduce the risk. The Restatement takes the factors without the algebra. It calls them the primary considerations bearing on reasonable care; it does not instruct courts to multiply.
The meaning of the Learned-Hand B < P * L formula is very much disputed, but one powerful reading of Carroll Towing is that it adopts cost-benefit analysis as the test for negligence. The reasonable person, so the story goes, analyzes the costs and benefits of her actions and does not act in such a way so as to impose costs that are not justified by their benefits. Economists might associate the Hand formula with the economic concept of efficiency, and specifically Kaldor-Hicks efficiency. (Follow this link for an explanation.)
Even if the Learned Hand formula is best interpreted as employing cost-benefit analysis or the economic idea of efficiency, it does not directly follow that the purpose of the law of negligence is itself to promote the most cost-beneficial consequences. It might be, for example, that a strict liability regime (rather than a negligence regime) will produce the best consequences. There are two different questions regarding the relationship between cost-benefit analysis and the reasonable person. (1) Does the reasonable person standard employ cost-benefit analysis as the criterion for negligence? And (2) Does cost-benefit analysis support the choice of negligence (as opposed to strict liability or no liability) as the rule governing nonintentional torts? Once the questions are separated, it is clear that they are different. It might be that the law employs a cost-benefit (Learned Hand) test as the standard of care in negligence cases, but that this approach itself is not the best when judged by cost-benefit analysis.
Immanuel Kant and the Reasonable Person as Respecter of the Interests of Others
Although many scholars interpret the Learned Hand formula as an endorsement of an economic approach to the reasonable person, others reject this move. The Hand formula can also be interpreted as reflecting an argument of principle (or fairness). At a very high level of generality, we might say that the reasonable person treats others with respect. This approach to the reasonable person is roughly correlated with the deontological approach to moral philosophy, most famously associated with Immanuel Kant and his notion of a categorical imperative. The reasonable person, we might say, acts so that the maxim of her action (the principle upon which she acts) could be willed as a universal law—or, to put it differently, the reasonable person treats others as ends-in-themselves and not only as means. In this vein, Ronald Dworkin has argued that the Learned Hand formula can be understood as reflecting the moral equality of persons.
Virtue Jurisprudence and the Aretaic Conception of the Reasonable Person
Yet another approach to the “reasonable person” might be derived from Aristotelian moral theory (or virtue ethics)—in particular from the idea that the focal standard for morality is the “virtuous agent,” i.e., the person who possesses the moral and intellectual virtues. What are these virtues? The moral virtues include characteristics such as courage, good-temper, and temperance. The intellectual virtues are sophia (theoretical wisdom) and phronesis (practical wisdom). A difficulty with an aretaic approach to the reasonable person standard is that this standard seems too demanding. The Aristotelian person of virtue is a phronimos, not a person of average ability but rather possessed of an extraordinary capacity to evaluate and choose.
And the winner is . . .
As you might guess, this is the point at which the Legal Theory Lexicon runs out of gas. Appropriately so. For this is a perennial question in legal theory—one for which simple and off-hand answers are hardly appropriate. But here is one more thing to consider. The contest between various interpretations of the “reasonable person” takes place at two different levels. First, there is the level of fit. Which conception of the “reasonable person” is most consonant with the way that idea is used in the law? Second, there is the level of justification. Which conception of the “reasonable person” is supported by what we know about moral philosophy and political theory? And of course, it may turn out that the answers to these two distinct questions diverge. The best conception of the reasonable person may not be the conception that is implicit in the law of torts.
The three conceptions discussed above are all proposals arrived at by reflection: each asks what reasonableness ought to mean and answers from the armchair. But reasonableness in the law is frequently applied by jurors, who are ordinary people using an ordinary word. What ordinary people mean by “reasonable” is something that can be investigated empirically. That is the project of experimental jurisprudence, which studies legal terms and concepts by testing how people actually deploy them. This might enable us to recover the folk conception of reasonableness — the idea that is actually employed by ordinary people.
The empirical findings about reasonableness are intriguing. Kevin Tobia asked subjects for reasonable quantities — a reasonable delay before a criminal trial, a reasonable number of hours’ notice before a landlord enters an apartment — and found that their answers fell between the average and the ideal, and were better predicted by a combination of the two than by either alone. On this evidence, the folk conception of reasonableness is a hybrid: partly a report of what is ordinary, partly a judgment about what is good. That result sits awkwardly with all three of our conceptions, none of which is a hybrid. We need to be cautious about these results. Evidence about the ordinary concept does not by itself tell us what the legal standard should be; that inference requires an argument at the level of justification. And critics of experimental jurisprudence argue that the intuitions that matter are those of legal experts, not those of survey respondents.
And here is another complication. The reasonable person may wear a different suit of clothes to a tort case than she does to a criminal law case. What then?
Conclusion
If you are a first-year law student reading this post, it is likely that you have recently or will soon make the acquaintance of the reasonable person. Understanding the reasonable person will not only be important to your study of torts and criminal law; the ideas with which you grapple in cases like Carroll Towing ramify throughout the law. Being able to articulate and argue about the proper interpretation of the reasonable-person standard equips you to understand debates about efficiency versus fairness (or deontology and consequentialism) that are fundamental to contemporary legal theory.
Related Lexicon Entries
Legal Theory Lexicon 008: Utilitarianism
Legal Theory Lexicon 009: Public Reason
Legal Theory Lexicon 010: Deontology
Legal Theory Lexicon 012: Virtue Ethics
Legal Theory Lexicon 024: Balancing Tests
Legal Theory Lexicon 026: Rules, Standards, Principles, Catalogs, and Discretion
Legal Theory Lexicon 031: Virtue Jurisprudence
Legal Theory Lexicon 032: Fit and Justification
Legal Theory Lexicon 060: Efficiency, Pareto, and Kaldor-Hicks
Legal Theory Lexicon 115: Tort Theory
Legal Theory Lexicon 118: Criminal Law Theory
Bibliography
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Mayo Moran, Rethinking the Reasonable Person: An Egalitarian Reconstruction of the Objective Standard (Oxford University Press 2003).
Stephen Perry, Cost Benefit Analysis and the Negligence Standard, 54 Vand. L. Rev. 893 (2001).
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Restatement (Third) of Torts: Liability for Physical and Emotional Harm § 3 (American Law Institute 2010).
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Link to the Most Recent Version of this Lexicon Entry
Legal Theory Lexicon 004: The Reasonable Person
This entry was last revised on August 30, 2026.
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