The article deals with some implications of radical uncertainty for participatory democracy, and more precisely for Participatory Technology Assessment. Two main forms of PTA are discussed. One is aimed at involving lay citizens and highlighting public opinion. The other is addressed to stakeholder groups and organisations, not only in terms of interest mediation but also of inclusion of their insight into a problem. Radical uncertainty makes 'intractable' many environmental and technological issues and brings into question traditional and new approaches to (...) policymaking. Its consequences are explored from the viewpoint of new science, deliberative democracy, and network governance. Radical uncertainty calls for a rethinking of the aims of public deliberation, and a reinterpretation of the divide between opinion- and position-oriented PTA. To look for a public opinion, understood as a shared principled view, can prove misleading, as can thinking of stakeholder participatory arrangements in the usual way. When facts and values overlap, and are deeply controversial, the only opportunity for mutual understanding may be to look for practical, 'local' answers, based on different positional insights. Moreover, radical uncertainty also affects interest determination and pursuit, and may enhance the opportunity of joint, inclusive, non-strategic issue definition and solution-devising. This vision of public deliberation is consistent with the idea of network governance. However, fragmentation can affect the effectiveness and legitimacy of participatory policies. Trying to handle fragmentation from the top, as many suggest, is unlikely to be successful. A more promising endeavour is to foster deliberative settings which, although positioned at the level of 'local' and often contingent networks and commonalities, are open to include 'Otherness' – other contexts, other problem definitions, other concerns. (shrink)