Sustainability: Ecological and economic perspectives

Admonitions to decision makers to "act sustainably" founder on conceptual ambiguities that transcend disciplinary boundaries and affect the definition and assessment of sustainability. In this article we address these underlying theoretical difficulties, paying special attention to two clusters of issues: reversibility and substitutability, and how to assess environmental values. In highlighting these two broad problem areas, we also note that cross-disciplinary disagreements cannot be resolved without making considerable progress in other areas of ecological and economic theory. We suggest that a "two-tiered" system might prove a useful beginning point for finding a more unified and interdisciplinary approach to decision making.