Threats to climate, biodiversity, soils, air and water join long-standing issues of poverty and vulnerability in demanding urgent action. Radical transformations are required in global institutions and infrastructures for provision of energy, food, water, mobility and livelihoods. So, political, economic and social – as well as environmental – stakes are high. Yet it is rarely the case that all details of the issues in question can be definitively pinned down (Gee et al., 2013). There usually remains significant scope for questions over: appropriate knowledges; causal processes; possible implications; and relevant actions. These are the dilemmas of what is often ambiguously called ‘uncertainty’, but more accurately described as ‘incertitude’ (Harremoes et al., 2001). AS we will see, specialist usages of ‘uncertainty’ can elide crucially different features of context – allowing irresponsible “pretence of knowledge” (Hayek, 1978). An overarching term like ‘incertitude’ helps avoid this.