the precautionary principle requires an active use of doubt, in the sense Descartes made canonical in his meditations. Before any action, I must not only ask myself what I need to know and what I need to master, but also what I do not know, what I dread or suspect. I must, out of precaution, imagine the worst possible, the consequence that an infinitely deceptive, malicious demon could have slipped into the false of apparently innocent enterprise.