New perspectives on reduction and emergence in physics, biology and psychology

This volume has grown out of a conference on Reduction and Emergence held in Paris, at the Ecole Normale Superieure, 12–15 November, 2003. Traditionally, and until quite recently, emergence and reduction were taken to be contrary notions: a theory T1—or more often, the phenomena described by that theory—was taken to be emergent with respect to another theory T2 if and only if it is impossible to reduce T1 to T2, although T1 and T2 appear to describe and explain the same natural systems or phenomena. This doctrine has recently been challenged by new conceptions of emergent phenomena which allow them to be scientifically explained and even reduced. If the distinction between emergent and resultant phenomena is to be upheld, the task is then to ground emergence on a new criterion independent of reducibility. This is closely linked to the search for an account of scientific reduction that avoids conceiving it in terms of syntactic derivability, as did Nagel’s classical account. It is well known since Feyerabend’s, Popper’s and Kuhn’s work that Nagel’s standards for reduction were too strong to be met by most real pairs of theories. Indeed, many if not all scientific reductions are accompanied by corrections to the reduced theory. There are now several models of such “approximate” reductions, situated somewhere between full conservation and radical elimination. To mention only a few, one important idea was to abandon the requirement of derivation of the reduced T1 from the reducing theory T2, to replace it by the weaker requirement of derivation from T2 of a theory T1* analogous to T1. Structuralism, which represents relations between theories by way of the relations between their