Murphy, Nancey. “Supervenience and the Downward Efficacy of the Mental: A Nonreductive Physicalist Account of Human Action."

In “Supervenience and the Downward Efficacy of the Mental: A Nonreductive Physicalist Account of Human Action,” Nancey Murphy sets out to answer the question: If mental events are intrinsically related to (supervene on) neural events, how can it not be the case that the contents of mental events are ultimately governed by the laws of neurobiology? The main goal of her essay, then, is to explain why, in certain sorts of cases, complete causal reduction of the mental to the neurobiological fails. To do so, she first considers the concept of supervenience, offering a definition that runs counter to the “standard account.” The concept of supervenience was introduced in ethics to describe the relation between moral and nonmoral (descriptive) properties; the former are not identical with the latter, but one is a “good” person in virtue of possessing certain nonmoral properties such as generosity. Supervenient properties are multiply realizable; that is, (in the moral case) there are a variety of lifestyles each of which constitutes one a good person. Murphy criticizes typical attempts at formal definitions of “supervenience” for presuming that subvenient properties alone are sufficient to determine supervenient properties. She argues that many supervenient properties are codetermined by context - this move recognizes constitutive relationships not only at the subvenient level but also at the supervenient level itself or between the level in question and even higher levels of organization.

Murphy argues that it is this participation of entities in higher causal orders by virtue of their supervenient properties that accounts for the fact of downward causation. In Donald Campbell’s original example, it is the functional properties of the termites’ jaw structure - their relation to a higher-level causal order - that allows for environmental feedback, resulting in modifications at the (subvenient) genetic level. These modifications are a result of selection among lower-level causal processes (Note: While Murphy takes feedback and selection among lower-level causal processes to be the essential ingredient in downward causation, Arthur Peacocke, in his essay in this volume, assimilates it to “whole-part influence”).

Murphy then turns to the issue of mental causation: How do reasons get their grip on the causal transitions among neural states? The key to answering this question is the fact that neural networks are formed and reshaped (in part, at least) by feedback loops linking them with the environment; the environment selectively reinforces some neural connections but not others. Murphy points out that it is not only the physical environment that plays a downward causal role in configuring neural nets, but also the intellectual environment. It is the fact that mental states supervene, in Murphy’s sense of the term, on brain-states - that is, that they are co-constituted by both brain-states and their intellectual context - that makes the occurrence of the brain-states themselves subject to selective pressures from the intellectual environment.

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