and often to public uncertainty about whether pesticides are harmful or not (Bosso 1987). How,
under these conditions, can further policy change occur? I argue that significant policy change in
the midst of conflicting policy images is more likely when advocacy groups and policy
entrepreneurs successfully introduce new principles to guide policy decision making. A policy
principle is the stated or unstated, formal or informal basis upon which policymakers deliberate
and make decisions. Images and principles are related to one another but constitute different
aspects of a policy discussion and debate. Images are more or less identifiable; they are the
frames or categories used by the media, public, and policymakers to discuss an issue. Principles
operate in the background, are frequently unstated, and are unlikely to be at the forefront of
public discussion. They are often assumed, but may at times be institutionalized in public policy.
For example, the cost-benefit principle has been written into the U.S. Federal Insecticide,
Fungicide, and Rodenticide Act. It directs the Environmental Protection Agency to consider the
potential environmental, economic, and social costs of pesticides and weigh these against their
expected benefits when making pesticide registration decisions.
It is even more difficult to change policy principles than to redefine an issue. This is due
in part to the often assumed, unstated, and deep-seated nature of policy principles. For example,
discussions of health care in the United States are largely guided by the assumption that health
care is a privilege, not a right. Advocating for a “rights” principle to guide public policy around
health care is a long-term, difficult process that requires people and policymakers to question
unrecognized assumptions and entrenched ways of thinking. At times, however, new principles
can take hold of the public and policymakers’ imaginations and become a new guide to
policymaking. Such shifts in principles can lead to dramatic policy changes that have broader
impact than, for example, simply banning a specific pesticide or pesticide ingredient. The 1996
U.S. Food Quality Protection Act, for instance, recognized the importance of taking into account
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Convention