 Finally, to wrap up this discussion of mechanism ascendant, an analogue of Craver’s (2007) problem of accounting for “constitutive mechanistic relevance”, that is, for determining which active components of a system are actually part of the mechanism for a given system phenomenon, has also re-emerged in recent discussions. Robert Rupert (2009) suggests that “integration” is a key criterion for determining which set of causally contributing mechanisms constitute the system for a task, based on the relative frequency with which sets of mechanisms co-contribute to causing task occurrences. He cashes frequency of co-contribution as the probability of the set for causing the cognitive task, conditional to every other co-occurring causal set. Felipe De Brigard (2017) challenges Rupert’s criterion, arguing that it cannot account for cognitive systems displaying two features, “diachronic dynamicity” along with “functional stability”. The frequency with which a given mechanism causally contributes to the same cognitive task (functional stability) can change over time (diachronic dynamicity). Although De Brigard emphasizes the critical importance of these features for Rupert’s integration criterion via a fanciful thought experiment, he also argues that they are a widespread phenomenon in human brains. Both features are found, for example, in evidence pertaining to the “Hemispheric Asymmetry Reduction in Older Adults”, in which tasks that recruit hemispherically localized regions of prefrontal cortex in younger adults show a reduction in hemispheric asymmetry in older adults. And both are found in “Posterior-Anterior Shift with Aging”, where a task increases activity in anterior brain regions while decreasing activity in posterior regions in older adults, relative to activity invoked by the same task in younger adults.