Two types of sustainability definitions are contrasted. ‘Social scientific’ definitions, such as that of the Brundtland Commission, treat sustainability as a relationship between present and future welfare of persons. These definitions differ from ‘ecological’ ones which explicitly require protection of ecological processes as a condition on sustainability. ‘Scientific contextualism’ does not follow mainstream economists in their efforts to express all effects as interchangeable units of individual welfare; it rather strives to express sensitivity to different types and scales of impacts that (...) present activities can exert on the future. We can therefore express the moral obligation to act sustainably as an obligation to protect the natural processes that form the context of human life and culture, emphasizing those large biotic and abiotic systems essential to human life, health, and flourishing culture. Ecosystems, which are understood as dynamic, self-organizing systems humans have evolved within, must remain ‘healthy’ if humans are to thrive. The ecological approach to sustainability therefore sets the protection of dynamic, creative systems in nature as its primary goal. (shrink)