Emergence and reduction

Claims about reduction or emergence appear in cases in which there are different levels of facts that have between them some kind of ontological connection by which one of them is 'made up' from the other. In the case of reduction, it is supposed that the reduced level of facts is 'nothing over' the reducing level of facts. In the case of emergence, on the other hand, it is supposed that the emergent level is something 'new' with respect to the emergence base. In both reduction and emergence some kind of ontological priority of one level with respect to the other is involved, as well as some kind of explanatory asymmetry between them. In recent years a lot of work has been devoted to different notions of ontological priority, like grounding and dependence, that might be useful for the clarification of the more traditional questions about the nature of reduction and emergence. This work presents and discusses various attempts to make that clarification.