Emergent Causation

The notion of an emergent property has aroused much recent discussion among both scientists and philosophers. Many quite different kinds of properties have been described as ‘emergent’, the only clear common factor being the broad idea that when a physical system of sufficient complexity is in a suitable configuration new properties ‘emerge’ in a way that could not have been predicted from the physical laws governing less complex or differently configured systems. Examples of putative emergent properties in the actual world can be found in biology, chemistry, in branches of physics dealing with complex systems, in computer science, and in the philosophy of mind. Many of the examples given by scientists belong to an ‘epistemological’ variety of emergence, where the emphasis is on the impossibility of predicting the presence of emergent features of macroscopic phenomena based purely on complete knowledge of the microscopic phenomena from which the macroscopic phenomena emerge. This kind of emergence is to be distinguished from an ‘ontological’ variety of emergence according to which the emergent phenomena are not merely unpredictable from base-level phenomena but are in some sense ontologically distinct from them. This is typically understood in terms of a failure of strong whole-part supervenience; the emergent property of the whole is not logically entailed by the properties of the parts and their mode of combination (I give a more precise formulation below). This latter kind of emergence has tended to attract more