Material flows vs. natural capital - What makes an economy sustainable?

In the discourse about sustainable development, 'constant natural capital' is frequently referred to as a criterion for ecological sustainability. Bur what is 'natural capital'? The concept will be analyzed by presenting arguments in favour of using the term and different versions of sustainability (strong and weak). Subsequently, a critique of the 'natural capital' concept is brought forward, from an ecological as well as from an economic perspective. Following this critique, the use of material inputs and the material input per unit of service (MIPS) as a measure for the environmental impact potential is suggested. Dematerialisation is understood to be an alternative management rule for sustainability. In conclusion, a change of perspective is proposed. Due to the conceptual and measurement problems associated with the 'constant-natural-capital' criterion (which refers to a stock), it seems more reasonable from a scientific as well as from a practical perspective to add flows (i.e. material inputs) to a decision criterion for whether a development is sustainable or not. (C) 1997 Elsevier Science B.V.