Available methods such as technology assessment and risk analysis have failed to predict the effects of technological choices. We need to give up the futile predictive ambitions of previous approaches and instead base decisions on systematic studies of alternative future developments. It will then be necessary to cope with mere possibility arguments, i.e., arguments in which a conclusion is drawn from a mere possibility that a course of action may have certain consequences. A five-step procedure is proposed for the assessment of such arguments. It includes (1) a search for mere possibility arguments pointing in different directions, (2) a scientific evaluation that may lead to the specification or refutation of some of these arguments, (3) two symmetry tests, (4) evaluation of the seriousness of the arguments in terms of novelty, spatio-temporal unlimitedness and interference with complex systems, and (5) hypothetical retrospection that aims at finding a course of action that will be defensible in retrospect.