One recently popular way to characterise strong emergence is to say that emergent entities possess novel causal powers. However, there is little agreement concerning the nature of powers. One controversy involves whether powers are single- or multi-track; that is, whether each power has only one manifestation type, or whether a single power can be directed towards a number of distinct manifestations. Another concerns how powers operate: whether a lone power manifests when triggered by the presence of a suitable stimulus, or whether powers operate mutually such that several powers must 'work together' to bring about a particular manifestation. This paper examines how these distinctions-which can be cross-combined to frame four distinct accounts of the nature of powers-bear on the debate between emergentists and reductionists.
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