The Reasonable Person

70 Pages Posted: 16 Jul 2011 Last revised: 22 May 2018

See all articles by Alan D. Miller

Alan D. Miller

Faculty of Law, Western University

Ronen Perry

University of Haifa - Faculty of Law

Date Written: July 7, 2011


The Article sets forth a conclusive and unprecedented answer to one of the most fundamental questions in tort law, which has bedeviled and divided courts and scholars for centuries: should reasonableness be a normative or a positive notion? Put differently, should the reasonable person be defined in accordance with a particular normative ethical commitment, be it welfare-maximization, equal freedom, ethic of care, etc., or in accordance with an empirically observed practice or perception? Only after answering this question can one move on to selecting a concrete definition of reasonableness. Our own answer is radical but inescapable: only normative definitions are logically acceptable.

The Article does not endorse a particular definition of reasonableness. Instead, it focuses on the fundamental choice between the two conflicting paradigms. We put forward and defend the thesis that normative definitions are categorically preferable to positive definitions, because the latter are logically unacceptable, whereas the former merely raise partially surmountable practical problems. Although the Article focuses on the reasonable person in torts, the implications of our analysis are far-reaching, because the concept of reasonableness prevails in most areas of American law.

Part I presents the most salient normative definitions of the reasonable person, namely those that stem from the ideas of welfare maximization, equal freedom, and the feminist ethic of care. It explains their practical weaknesses, and shows that these weaknesses surface mostly at the margins, and can be alleviated to some extent. In contrast, Part II shows that a positive definition of reasonableness is a logical impossibility. We do not study any specific positive definition but construct a formal model of the reasonable person that allows us to study all such definitions simultaneously. The formal model is built with tools from a branch of economics known as social choice theory, and is analogous to the groundbreaking theorem for which Kenneth Arrow was awarded the Nobel Prize in 1972. We impose five axioms on the reasonable person; all of them are necessary characteristics of any positive definition. We then prove that a positive definition cannot possibly satisfy all five. Consequently, any empirical methodology used to study the reasonable person is necessarily invalid.

Keywords: Reasonable Person, Welfare Maximization, Kant, Feminist, Feminist Jurisprudence, Ethic of Care, Normative, Positive, Empirical Estimation, Axioms, Social Choice, Impossibility

JEL Classification: D71, K00, K13

Suggested Citation

Miller, Alan D. and Perry, Ronen, The Reasonable Person (July 7, 2011). New York University Law Review, Vol. 87, pp. 323-392, 2012, Available at SSRN:

Alan D. Miller (Contact Author)

Faculty of Law, Western University ( email )

1151 Richmond Street
London, Ontario N6A3K7


Ronen Perry

University of Haifa - Faculty of Law ( email )

Mount Carmel
Haifa, 3498838


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