Non-reductive physicalism about the mind and neuroscience

At this recent conference in Florence I presented a paper on how legal scholar Stephen Morse uses John Searle’s non-reductive theory to critique the utility of neuroscience to law. Michael S. Moore, also at the conference, proved to be a very strong ally in my attempts to convince Stephen that non-reductivism is wrong-headed. (That is to say, Michael made many of the same arguments I did, but in a more convincing and succinct way.) Both Michael and I think non-reductivism is wrong-headed. In my next blog post I’ll detail some of history of the position, and how it essentially recreates the problem of mental causation that physicalism was meant to solve.

In this post, I want to explore what Searle’s theory really means with regard to the utility of neuroscience to law. The theory, termed ‘biological naturalism,’ consists in four theses (Searle 2004):

1.     Consciousness is a real thing in the world that cannot be reduced to its neurobiological basis, because “such a third-person reduction would leave out the first person ontology of consciousness.”

2.    Conscious states, however, are causally reducible to neurobiological processes – they are not something ‘above and beyond such processes.

3.    Portions of the brain system composed of neurons are conscious, although individual neurons are not.

4.    Conscious states function causally – they have physical effects.

The causal efficacy of mental states (prong four) relies upon their causal reducibility (prong two). Thus Searle claims that a conscious mental state’s causal properties can be explained by looking to their place within a physical causal system. Searle says, “We can say that phenomena of type A are causally reducible to phenomena of type B, if and only if the behavior of A’s is entirely causally explained by the behavior of B’s, and A’s have no causal power in addition to the powers of B’s” (Searle 2004). The causal properties of a conscious state are identical with the causal properties of the physical state that realizes it.

However, Searle maintains a non-reductive position by claiming that the conscious phenomenal properties of a mental state are not reducible (Searle 2004): what can’t be reduced is the first-person account of what it feels like to undergo a particular physical state. Searle thus claims we can make a causal reduction, but not an ontological one, because an ontological reduction would lose the point of the concept of consciousness (Searle 2004). (An ontological reduction involves a claim that an object or even of a certain type can be shown to be nothing more than objects or events of another type, in the way that a rock can be shown to be nothing more than atoms arranged in a certain way.) According to Searle, the point of the concept of consciousness is to capture the first person, subjective experience, and this subjective phenomenal feel of a conscious state cannot be seen or understood via the underlying brain state.

I agree with Searle that examination of a brain state (at least using current scientific means) will necessarily leave information of how this brain state feels to the holder of the state. But what is particularly interesting about Stephen Morse’s use of Searle’s non-reductivism is how the theory assigns causal properties. Under Searle’s theory, conscious mental states are causal (prong 4). For a mental state to be causal, it must be causal via mental content, not just due to its underlying physical state. This is because if a mental state isn’t causal via its content, but only via its relationship with an underlying physical state, the mental isn’t causal but epiphenomenal: in this case the mental state itself wouldn’t be causal, it would only be a powerless “ride-along” to an underlying physical state.

I think what follows from all of this is that the content of the mental state which carries the causal properties is reducible to its underlying physical state (even if the phenomenal “feel” of the mental state is not). Searle could argue that some aspect of mental content – its intentionality, for example – is inextricably tied to the state’s conscious aspect and not related to its underlying physical state. But this would mean that intentionality qua intentionality did no causal work, which seems like an unfortunate result. To save mental causation, it would seem that one would want the intentional content of mental states – e.g. the belief it is raining (out there) – to be the reason why I get my umbrella. But to say that this intentional content is causally reducible to an underlying physical state is to say that intentional states themselves – their content, not their feel – can be understood in terms of the brain states they supervene upon. In other words, this mental content has to exist in the physical realm to realize its physical causal powers.

So according to Searle’s theory, where a conscious mental state’s causal properties are reducible to its underlying brain state, the causally efficacious content of a mental state is also reducible to its underlying physical state (even though the “feel” of this content is not). And to preserve full-bodied mental causation, this is going to have to be aspects of the mental that matter, including its content.

The flip side of this analysis is that the aspects of the mental that aren’t reducible – phenomenal consciousness – does no causal work in addition to this mental content. That is, conscious mental states qua conscious mental states do no causal work.

From the perspective of the law, this means that the content of an intentional mental state – e.g. the desire to kill – which we understand to reliably have causal properties, can be understood in terms of its underlying physical state. Further, the phenomenal feel of the desire to kill does no causal work in addition to the content of the mental state that can be physically understood. Thus when a judge or jury is looking for the mental state that is causally linked to criminal harm, they are also implicitly looking for whatever physical state realizes the content of that mental state. Which means that, at least in cases where we have a reliable way of translating neuroscientific information about brain states into information about mental content, neuroscience may be a useful tool in understanding that content.

Thus it doesn’t seem that Searle’s theory can be used to discount the utility of neuroscience to law. Indeed, Searle’s theory may support the use of neuroscience in law, although this conclusion is subject to many caveats regarding neuroscience’s methodological limitations, which will be the topic of a later blog post.

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