Modern developments of scientific medicine have uncovered and created uncertainties and risks that were previously not known or experienced; the stakes have become very much higher. The rise in public expectation, however, is paralleled by a lowered tolerance of uncertainty. Metaphors of "deliverance" and "disaster" abound in discussions of scientific discovery, reflecting differing conceptions and philosophies about errors and mistakes, and the role they play in the physical universe, the biosphere, and human affairs. These concerns highlight the difficulties and dilemmas of finding scientifically adequate, culturally appropriate, and socially effective ways of appraising and controlling risk.