Evolving knowledge and the precautionary principle

Existing formulations of the Precautionary Principle tend to be too weak or too strong. They are too weak if they limit themselves to rejecting, for policy purposes, the bias in scientific research toward minimization of Type I error. This position is already embodied in classical decision theory. They are too strong if they demand proof of safety on the part of producers of potentially hazardous products and processes; this would eliminate too many beneficial activities. An intermediate position is proposed: the function of precaution is to take into account what we do not know as well as what we do about the consequences of human activity. This leads to a meta-rule: decision-making is precautionary if unpredictable revisions in knowledge lead equally to unpredictable revisions in regulation. In the context of evolving knowledge about the ecological impacts of human activities, this implies a shift toward significantly greater protection.