The following is an exposition of Derek Jeffreys’ Aristotelian-Thomistic critique of the appropriation of the non-reductive physicalist doctrine of emergentism for Christianity.
On the one hand, the non-reductive physicalist doctrine of emergentist is helpful for theists insofar as it demonstrates the incoherence of reductive physicalist attempts to do away with the existence of mental properties and their capacity for downward causation. On the other hand, it is hostile towards theistic beliefs insofar as it seeks to replace the soul with these mental properties. A helpful way of remedying this problem is by integrating an Aristotelian-Thomistic account of causality with an emergentist understanding of the human person.
While neurophysiological entities may be necessary for the spatiotemporal human to possess minds, non-reductive physicalists err in thinking that they are sufficient for the existence of mind. Indeed, it is hard to see how an immaterial soul can emerge from neurophysiological basal conditions, especially one that can survive death.
Nancey Murphy’s Christian account of non-reductive physicalist emergentism will be our interlocutor. For her, the emergentist account of supervenience, and the capacity for downward causation it provides, is the key to eliminating reductionism. But this does not mean that emergentism can coherently explain the genesis of consciousness.
For Derek Jeffrey’s, this non-reductive physicalism ignores the Thomistic principle of causality according to which no effect can be greater than its cause. In order to understand this Thomistic account of causality, we must understand the Thomistic account of “nature.” Jeffrey’s recommends the adoption of the Thomistic understanding of perfection and its “regularity conception of causality.”
She must do this, if she is to be consistent, he argues, because it is necessary to defend the idea that an entity with a nature possess causal power. Finally, he insists that Christian philosophers of science, mind and religion pay closer attention to metaphysics, particularly as regards its ramifications for causality, in this case, as non-reductive physicalism, however much closer it may be to a theistic account of the human person than reductive physicalism, requires such an account of causality for its coherence.
As Jeffrey’s points out, Murphey dissects reductionism into its different meanings. The methodological reductionist believes that an entity, such as a disease, can be analyzed purely in terms of its biochemical processes. The causal reductionist adopts a position similar to a non-reductive physicalist who is nonetheless a determinist, such as Roger Sperry. From this perspective, the mind might not be reducible to the neurological or neurochemical sum of its parts, but these lower-level basal properties would still determine the behavior of the higher-order process of the mind to which it gives rise. The ontological reductionist disagrees with the non-reductive physicalist in arguing that higher-level entities can be reduced to the sum of its parts.
The non-reductive physicalist, as Murphy points out, accepts ontological reductionism, in requiring material basal conditions for higher-order mental properties, but rejects reductive materialism, because they believe mental properties actually exist, and they reject causal reductionism, because they believe that these existing mental properties exhibit causal efficacy or downward causation. As Jeffreys points out, there is a sense in which the non-reductive physicalist denies the existence of the mind (as a substance) without denying the existence of the mental. Ultimately, however, the uncritical adoption of the non-reductive physicalist solution is problematic because it makes all experience, even religious experience, dependent upon material properties.
The non-reductive physicalist, as Murphy notes, appeals to the concept of supervenience over and against causal reductionism. The mind supervenes on matter and exerts causal efficacy over it. Thus, mental events are not (always) the result of physical events in the brain. Murphy notes that the causal reductionist is incapable of demonstrating that mental states are purely the result of brain states in every circumstance. Thus, the question of circumstance and interpretation of events becomes highly important in the battle against reductive physicalism. Murphy’s example, as Jeffreys notes, has to do with electrical shocks. Of two shocked individuals, one may experience it as cold whereas the other experiences it as hot. In any case, it is clear that or circumstantial description and lived experience of the event can only be meaningfully articulated in terms of mental events rather than purely physiological events.
Jeffreys notes, however, that epiphenomenalists and emergentists alike have both appealed to the concept of supervenience. As such, it does not necessarily do away with reductive materialism. The epiphenomenalist, for example, believes that mind supervenes on matter, but denies that the mind has any causal efficacy. Appeal to supervenience in and of itself does not necessarily refute causal reductionism. It simply preserves the existence of mental states without according it any causal efficacy.
Jeffreys, Derek (2004). The Soul is Alive and Well:
Non-reductive Physicalism and Emergent Mental Properties. Theology and Science, Vol 2, No. 2, 2004 (dx.doi.org/10.1080/1474670042000261105 )