The precautionary principle and justified risk aversion

The Precautionary Principle (PP) urges us to be cautious when we face a threat of serious damage to the environment or human health, even where there is scientific uncertainty concerning the threat. PP appears to go beyond ordinary decision theory by taking more seriously the risk of very negative outcomes. Some attempts to regard PP as a substantive addition to decision theory are criticized. It is better, I argue, to regard PP as concerned with the proper setting up of a decision problem, to which decision theory can then be applied. Importantly, PP urges special attention to particularly bad potential outcomes. I identify several reasons for this special attention. One reason concerns ethical principles and constraints. I identify some additional reasons as well, which concern some easily neglected forms of harms that cluster among the particularly bad potential outcomes.