Arthur Allen Leff

Arthur Allen Leff (1935–1981) was a professor of law at Yale Law School who is best known for a series of articles examining whether there is such a thing as a normative law or morality. Leff answers this question in the negative and follows the consequences to their logical conclusions.

Leff's first major work Economic Analysis of the Law: Some Realism About Nominalism is putatively a book review of Richard Posner's Economic Analysis of the Law. In actuality it is a critique of the use of any single methodology to provide normative rules for law and morality. The article is still, today, the main critique of Posner's work and economic analysis generally and is usually read in graduate seminars on Economic Analysis (though sometimes misidentified as the Legal Realist critique). Leff makes two fundamental proposition in Some Realism About Nominalism: (1) that all models are only very limited views of the real world. When Posner views the world through the economic model much more is hidden than is revealed; (2) there is no system of logic for preferring one model (e.g. economic, social, political) over another unless an axiom is inserted early on into that system of logic. Leff notes that the opening of Posner's work does just that—inserts a proposition that rational economic behavior is to be preferred to other behavior. Leff follows his insight to its logical conclusion and notes that similarly there is no way, using logic, to prove that any particular act, no matter how horrible, is normatively wrong. Put it another way, one can never prove to another person that a particular set of behaviors is right or that a different set of behaviors is wrong. He states:

Leff continues his critique of attempts to find normative rules in law and morality in Law and Technology: On shoring up a Void, Unspeakable Ethics, Unnatural Law (alluding to the title of a collection of stories by Donald Barthelme), and his review of Robert Unger's Knowledge and Politics in the form of a letter from The Devil. In these works, Leff attempts to directly address whether a normative morality can exist without God. Leff answers the question in the negative. Leff states that absent an ultimate authority figure (i.e. God) handing down moral laws from on-high there is no reason for any person to prefer one set of behavior identified as "moral" to another. Leff terms this "the Grand Sez Who." In particular, it is impossible to resolve the conflict between the rights of the individual and the power of the collective, even though much of the time we can pretend that, for instance, the Constitution tells us where to draw the line. There are bound to be cases where we are left on our own, with no authoritative referee; there is no "brooding omnipresence in the sky", in the words of Oliver Wendell Holmes, Jr., whom Leff quotes approvingly.

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