 Finally, it has recently been proposed that a distinctive form of physical realization comes through implementing mechanisms: enduring structures of organized components that realize higher-level role functions, endowing higher level entities with novel, non-aggregative behaviors and properties (see Machamer et al. 2000, Craver 2007, and  entry on mechanisms in science).  Craver (2007) argues that in neuroscience and psychology in particular, we should think of minded biological agents as constituted by a hierarchy of mechanisms (or networks of such mechanisms). While he avoids use of the term “emergence”, which he associates with strong emergence (2007: 16), he is plausibly taken to advance a distinctive form of weak emergence. He defends the reality of such high-level, fully-realized powers on the grounds that they satisfy the conditions for causal relevance on the (manipulationist) account of causal explanation that he favors (2007: 216–220). Haug (2010) develops a mechanistic account of realization incorporating a distinction between what he calls “constitutive” and “integrative” mechanisms, associated with two distinct roles mechanisms play in the realization of special science properties. He argues that his mechanistic account contrasts favorably with determinable/determinate approaches (and more generally, “proper subset of powers” approaches) to realization, and that it provides a principled basis for claims of multiple realizability. (Gillett 2016 also emphasizes realizing mechanisms associated with novel powers in his account of emergence. But as he rejects physical causal closure, his account will be discussed under the rubric of strong emergence in  section 4.)