Grunwald (2004, p 152): ‘‘Sustainable development is a normative societal principle, and science makes indispensable contributions to its realization [...] The knowledge for sustainable development is provided on quite different levels and in various manners: [...] Sustainability assessment: whether certain effects and tendencies are to be interpreted as sustainability problems cannot be ascertained from empirical observation or simulation alone, but, rather, criteria have to be defined according to which observations can be classified as more or less relevant for sustainability, or even as sustainability deficit [...] Ranking of sustainability deficits: analysis of the sustainability situation also has to concern itself with assessment of the urgency of certain sustainability problems as opposed to others, and with setting priorities.’’