151 U. Pa. L. Rev. 1003 (2002-2003)
Beyond the Precautionary Principle

handle is hein.journals/pnlr151 and id is 1017 raw text is: BEYOND THE PRECAUTIONARY PRINCIPLE

CASS R. SUNSTEIN'
The precautionary principle has been highly influential in legal systems all
over the world. In its strongest and most distinctive forms, the principle im-
poses a burden of proof on those who create potential risks, and it requires regu-
lation of activities even if it cannot be shown that those activities are likely to
produce significant harms. Taken in this strong form, the precautionary prin-
ciple should be rejected, not because it leads in bad directions, but because it
leads in no direction at all. The principle is literally paralyzing-forbidding
inaction, stringent regulation, and everything in between. The reason is that
in the relevant cases, every step, including inaction, creates a risk to health, the
environment, or both. This point raises a further puzzle: Why is the precau-
tionary principle widely seen to offer real guidance? The answer lies in identi-
fiable cognitive mechanisms emphasized by behavioral economists. In many
cases, loss aversion plays a large role, accompanied by a false belief that nature
is benign. Sometimes the availability heuristic is at work. Probability neglect
plays a role as well. Most often, those who use the precautionary principle fall
victim to what might be called system neglect, which involves a failure to at-
tend to the systemic effects of regulation. Examples are given from numerous
areas, involving arsenic regulation, global warming and the Kyoto Protocol,
nuclear power, pharmaceutical regulation, cloning, pesticide regulation, and
genetic modification offood. The salutary moral and political goals of the pre-
cautionary principle should be promoted through other, more effective methods.
INTRODUCTION
All over the world, there is increasing interest in a simple idea for
the regulation of risk: In case of doubt, follow the precautionary princi-
ple.' Avoid steps that will create a risk of harm. Until safety is estab-
Karl N. Llewellyn Distinguished Service Professor of Jurisprudence, Law School
and Department of Political Science, University of Chicago. I am grateful for valuable
comments from Peter Dorman, Leeka Kheifets, Jack Knetsch, Saul Lev'more, Eric Pos-
ner, Indra Spiecker, Adrian Vermeule, Jonathan Wiener, and the participants in the
Midwest Faculty Seminar. I am also grateful to Martha Nussbaum for helpful discus-
sions.
I For general discussions of the precautionary principle, see INTERPRETING THE
PRECAUTIONARY PRINCIPLE (Timothy O'Riordan & James Cameron eds., 1994);
PROTECTING   PUBLIC   HEALTH   &   THE  ENVIRONMENT:      IMPLEMENTING   THE

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