Accidents and Aggregates

Abstract

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