International Conference on Whole Life Urban Sustainability and its Assessment M. Horner, C. Hardcastle, A. Price, J. Bebbington (Eds) Glasgow, 2007 The argument against a reductionist approach for assessing sustainability Alexandros Gasparatos a,* , Mohamed El-Haram a , Malcolm Horner a a,* Construction Management Research Unit, Division of Civil Engineering, University of Dundee, Fulton Building, Dundee, DD1 4HN, Scotland. ABSTRACT Both sustainability and sustainable development continue to remain elusive concepts even now, 20 years after the Brundtland Commission report that brought them into prominence. There is no consensus over their definition. This situation most likely stems from the fact that sustainability science encompasses the need to address a wide set of issues over different time and spatial scales and thus inevitably accommodates opinions from diverse branches of knowledge and expertise. However, despite this multitude of perspectives, progress towards sustainability is usually assessed through the development and utilisation of single sustainability metrics such as monetary models, composite sustainability indices and biophysical metrics including emergy, exergy and the ecological footprint. But is it really justifiable to assess the progress towards sustainability by using single metrics? This paper argues that such a choice seems increasingly unjustifiable not least due to these metrics’ methodological imperfections and limits. Additionally, our recent awareness of economies, societies and ecosystems as complex adaptive systems that cannot be fully captured through a single perspective further adds to the argument. Failure to describe these systems in a holistic manner through the synthesis of their different non-reducible and perfectly legitimate perspectives amounts to reductionism. An implication of the above is the fact that not a single sustainability metric at the moment can claim to comprehensively assess sustainability. In the light of these findings this paper proposes that the further elaboration and refinement of current metrics does not seem sufficient to produce frameworks for comprehensive sustainability assessments. Adoption of diverse metrics seems more likely to be the key for more concrete sustainability assessments. This methodological pluralism coupled with stakeholder involvement will most likely culminate in better informed policy making. Key words: sustainability assessment, sustainability metrics, reductionism