Boston University School of Law

Ambiguity About Ambiguity:
An Empirical Inquiry into Legal Interpretation

Ward Farnsworth

Dustin F. Guzior

Anup Malani

Boston University School of Law Working Paper 09-50
(October, 2009)

University of Chicago, Public Law Working Paper No. 280
(October, 2009)


Most scholarship on statutory interpretation discusses what courts should do with ambiguous statutes. This paper investigates the crucial and analytically prior question of what ambiguity in law is. Does a claim that a text is ambiguous mean the judge is uncertain about its meaning? Or is it a claim that ordinary readers of English, as a group, would disagree about what the text means? This distinction is of considerable theoretical interest. It also turns out to be highly consequential as a practical matter.

To demonstrate, we developed a survey instrument for exploring determinations of ambiguity and administered it to nearly 1,000 law students. We find that asking respondents whether a statute is “ambiguous” in their own minds produces answers that are strongly biased by their policy preferences. But asking respondents whether the text would likely be read the same way by ordinary readers of English does not produce answers biased in this way. This discrepancy leads to important questions about which of those two ways of thinking about ambiguity is more legally relevant. It also has potential implications for how cases are decided and for how law is taught.

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Ward Farnsworth Contact Information

Boston University School of Law
765 Commonwealth Ave
Boston, MA 02215
Phone: (617) 353-4008 (office)
Fax: (617) 353-3077 (office)

Dustin F. Guzior Contact Information

 J.D. Candidate, 2010
 Boston University School of Law
 Boston, MA

Anup Malani Contact Information

University of Chicago - Law School
1111 E. 60th Street
Chicago, IL 60637
Phone: (773) 702-9602
Fax: (773) 702-0730

Faculty Research Fellow
National Bureau of Economic Research (NBER)
1050 Massachusetts Avenue
Cambridge, MA 02138

University Fellow
Resources for the Future
1616 P Street, NW
Washington, DC 20036


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