Accidents and Aggregates

75 Pages Posted: 29 Apr 2017 Last revised: 23 May 2018

See all articles by Lee Anne Fennell

Lee Anne Fennell

University of Chicago - Law School

Date Written: June 8, 2017


Tort law deals in lumps. It responds not to the innumerable fine-grained acts of risk creation that each of us performs every day but rather to large, discrete, harmful events — “accidents.” And it responds to those events in a binary way, converting unruly facts into an on/off judgment about liability. This operation, characteristic of much of law, resembles the “thresholding” process used to convert grayscale images to black and white. If tort law aspires to produce patterns of liability that will deliver appropriate incentives for action, how should it isolate and evaluate the sample of risk-related behavior connected to the accident? This paper focuses on the implicit but powerful role that aggregation — of behavior, precautions, and events — plays in the determination of liability. These aggregative choices determine how large a slice of an injurer’s conduct tort law will capture within its viewfinder, and how tight the causal connection must be between the shortfalls observed there and the accident at hand. The analysis here also sheds light on questions of legal thresholding that emerge in other doctrinal areas.

Keywords: torts, negligence, strict liability, aggregation, lapses, causation

Suggested Citation

Fennell, Lee Anne, Accidents and Aggregates (June 8, 2017). 59 William & Mary Law Review 2371 (2018), University of Chicago Coase-Sandor Institute for Law & Economics Research Paper No. 810, U of Chicago, Public Law Working Paper No. 625, Available at SSRN: or

Lee Anne Fennell (Contact Author)

University of Chicago - Law School ( email )

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Chicago, IL 60637
United States
773-702-0603 (Phone)

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