The concept of emergence has seen a significant resurgence in philosophy and the sciences, yet debates regarding emergentist and reductionist visions of the natural world continue to be hampered by imprecision or ambiguity. Emergent phenomena are said to arise out of and be sustained by more basic phenomena, while at the same time exerting a "top-down" control upon those very sustaining processes. To some critics, this has the air of magic, as it seems to suggest a kind of circular causality. Other critics deem the concept of emergence to be objectionably anti-naturalistic. Objections such...