Is Nonreductive Physicalism Viable?

Contents

1. Introduction

2. The Psycho-Neural Identity Theory

3. Functionalism

4. Anomalous Monism

5. Global Supervenience

6. Metametaphysical Frameworks for the Philosophy of Mind References

1. Introduction

In this essay, I want to cast doubt on the idea of nonreductive physicalism. I will do that by a kind of pessimistic meta-induction. Therefore, I will introduce some main theories concerning the relation of the mental and the physical which were intended to support nonreductive physicalism. In order to motivate these accounts, I shall briefly outline the psycho-neural identity and its problems. I intend to confront each of the nonreductive theories with at least one major difficulty. This will lead to a more fundamental reflection on the methodology of inquiring into the metaphysics of mind. Furthermore, I will sketch some possible routes that one might take if the answer to the title of this paper would be negative.

2. The Psycho-Neural Identity Theory

In 1959 J.J.C. Smart formulated what is now known as the psycho-neural identity theory. According to Smart, sensations (as examples of types of mental events) are strictly identical with brain processes. Smart comes to believe this because of the success he saw science has had in explaining the world and because of the universal claim of physics as well as the principle of simplicity that should govern our choice of theory: “science is increasingly giving us a viewpoint whereby organisms are able to be seen as physico- chemical mechanisms: it seems that even the behavior of man will one day be explicable in mechanistic terms” (Smart 1959, 142). And in the sentence following this passage, Smart formulates the basic ontological view of every physicalism: “There does seem to be, so far as science is concerned, nothing in the world but increasingly complex arrangements of physical constituents.” (Smart 1959, 142) Therefore, Smart cannot believe that there could be anything that transcends this physical order. If we think that Occam ’ s razor is an epistemically valuable principle, we should not assume that the mental is not taken into account in this worldview: “That everything should be explicable in terms of physics […] except the occurrence of sensations seems to me to be frankly unbelievable.” (Smart 1959, 142) That means it is more reasonable to think that there is nothing over and above the physical. The mental would either pose an exception to the laws of nature or highly complex psycho-physical laws would have to be found. Both seems improbable to Smart.

As I mentioned at the beginning of this section, Smart endorses a strict identity of sensations and brain processes. Therefore, mental and physical events are not merely correlated, which would presuppose a dualism, but are identical like “lightning is electric discharge” (Smart 1959, 145), i.e. sensations are brain processes. Accordingly, statements which are supposedly about sensations in fact refer to brain processes, even if we do not know that or intend to do so (just like referring to the planet Venus by ‘morning star’). However, this does not mean that “sensation statements can be translated into statements about brain processes” (Smart 1959, 144).

To be precise, we have to classify Smart’s account as a type-type identity theory because mental types like pain are identified with c-fibres firing. Insofar as strict identity involves necessity, it would suffice to find one counterexample, where some being is in pain without its c-fibres firing, in order to disprove the strict identity relation. Indeed, there seems to be other creatures who have a different neurophysiology from us humans, but to whom we would nonetheless attribute states of pain. This fact has been called the multiple realizability of the mental and as we have seen it cannot be accounted for by Smart’s reductive physicalism. This is why in the decades following Smart’s article a variety of nonreductive approaches have been developed, which do not identify mental types with physical types. One of them is functionalism, on which we will focus on in the next section.

3. Functionalism

In 1967 Hilary Putnam published an article we now know by the name “The Nature of Mental States” (originally “Psychological Predicates”). In this paper, he proposed a functionalist theory of the mental which is able to integrate the multiple realizability of the mental. To illustrate this, we can think of different kinds of chairs (concerning material and form) which all share the same basic function, namely that we can use them to sit on them. As this chair is a functional kind and not a natural kind so are mental states. Mental states can be realized in different ways according to this theory. One consequence of this approach is that maybe even machines could realize mental states. Like humans perceive their environment and react to stimuli, computers process inputs and algorithmically produces outputs. Mental states are internal states of these systems that causally mediate the input and output. (Cf. Kim 2011, 169) The basic thesis of functionalism does not even commit itself to physicalism. However, as long as one does not believe in angels or a Cartesian res cogitans as a separate substance, functionalism is strongly associated with physicalism. (Cf. Kim 2011, 130) Therefore, we can assume that the realizations of functional states (mental states) are physical.

For mental properties are multiply realizable, the question arises if they are disjunctive properties (according to the disjunction of their realizers). This problem was dealt with in Jaegwon Kim’s 1992 article “Multiple Realization and the Metaphysics of Reduction”. In it Kim showed that pain, for instance, is a disjunctive kind and therefore nonnomic, that means that general mental terms of this kind do not pick out natural kinds in the world and therefore cannot appear in laws of nature. Consequently, we could not have a unified science of pain in general, but maybe a variety of psychologies about human-pain, salamander-pain or heptapod-pain if we stick to thesis of multiple realizability. By this fragmentation of psychology, functionalism (including multiple realizability) achieves the opposite of what it set out to do. Functionalism was intended to save the autonomy of psychology from reductive accounts that would, in principle, make it superfluous.

Another associated problem arises if we consider the causal power of mental properties. (MacDonald & MacDonald 1986 distinguish ‘causal efficacy’ and ‘causal relevance’. For them the problem of mental causation is about the causal relevance of instantiated mental properties.) Mental properties do not have any causal power that is independent of their physical realizers. And because of the plurality of possible realizers which have different causal structures, mental properties lack causal unity which makes it hard to establish nomic relationships between them and other properties, rendering them scientifically useless. (Cf. Kim 2011, 186)

Furthermore, Ned Block argued in his paper “Troubles with functionalism” (1978) that functionalism is confronted with a dilemma: Either functionalism is too liberal in ascribing mentality, like behaviorism, or chauvinistic like the psycho-neural identity theory in the sense that it excludes many beings from having mental states that could be counted as having them. Therefore, according to Block, functionalism does not fare much better than its opponents. Block says: “So, necessary conditions for mentality that are postulated by functionalism are in one respect stronger than those postulated by behaviorism.” (Block 1978, 262) That is because functionalism requires internal states that have a certain causal profile. On the other hand, functionalism is more liberal because it does not “unfairly exclude those poor brainless creatures who nonetheless have minds” (Block 1978, 265). According to Block, functionalism cannot escape this dilemma wherefore its viability can be questioned.

4. Anomalous Monism

In 1970 Donald Davidson formulated an account known as anomalous monism. In contrast to the psycho-neural type-type identity theory, Davidson’s approach is based on a token identity of mental and physical events. Accordingly, it does not assume lawlike relations between the mental and the physical: “there are no strict deterministic laws on the basis of which mental events can be predicted and explained” (Davidson 2001¹⁹⁷⁰, 208). Although this implies that the mental cannot be reduced to the physical, according to Davidson, this is not supposed to mean that the mental is something over and above the physical: “Anomalous monism resembles materialism in its claim that all events are physical, but rejects the thesis that, usually considered essential to materialism, that mental phenomena can be given purely physical explanations” (Davidson 2001¹⁹⁷⁰, 214). Therefore, anomalous monism can count as a kind of nonreductive physicalism. Now, whether an event is physical or mental depends, according to Davidson, on how we can describe it: “an event is physical if it is describable in a purely physical vocabulary, mental if describable in mental terms” (Davidson 2001¹⁹⁷⁰, 210).

However, one could object to Davidson’s token identity theory, as Andrew Melnyk has, that it is not sufficient for physicalism. As we have seen, according to Davidson, an event can have both physical and mental properties if it can be described in respective terms. The problem now is “that the event-identity claim tells us nothing about the relations between the single event’s having the mental property that it has and its having the physical property that it has” (Melnyk 2008, 1285). The token identity theory does not tell us why and how it is that the mental properties the event has is nothing over and above the physical properties it has.

Another very problematic assumption Davidson makes is “that where there is causality, there must be a law” (Davidson 2001¹⁹⁷⁰, 208). This is called the principle of the nomological character of causality. For, Davidson assumes that the mental is not governed by laws, he would actually have to exclude it from being causally relevant. This could, however, lead to an epiphenomenalism (cf. Kim 2011, 208). As Kim points out, it would be advisable to look out for different and non-nomological theories of causation (e.g. counterfactual accounts) that would allow mental events to be efficacious qua being mental and not just because they are identical with physical events (cf. Kim 2011, 209).

5. Global Supervenience

Another idea that was also put forward by Davidson is the supervenience of the mental on the physical (cf. Davidson 2001¹⁹⁷⁰, 214). That means that mental properties are somehow fixed or determined by physical properties (an asymmetrical relation). So-called global supervenience has been introduced as a nonreductive physicalist conception. Its core thesis is: “any two possible worlds (within a certain class) that are exactly alike physically are exactly alike mentally” (Melnyk 2008, 1286).

As with anomalous monism, Melnyk holds that global supervenience is not sufficient for physicalism. There are two main problems. On the one hand, the supervenience relation of mental and physical properties is too lose as a connection in order for mental properties to count as causes, considering the principle of the causal closure of the physical, according to which every physical event has a sufficient physical cause. (Cf. Melnyk 2008, 1287 [following Kim]) On the other hand, a more serious problem could be that supervenience means that the physical necessitates the mental, but that the theory fails to supply an account of “what explains this necessitation or even that it has an explanation. (The identity of every mental type with a physical type would explain the necessitation; but it would also be reductive.)” (Melnyk 2008, 1287) Therefore, an inference to the best (or easiest) explication would result in a reductive physicalism. For an alternative one would need a nonreductive explanation of the necessitation.

6. Metametaphysical Frameworks for the Philosophy of Mind

As we saw in the last three sections, the most prominent kinds of nonreductive physicalism that try to overcome the limitations of the psycho-neural identity theory are confronted with grave problems of their own. This could lead us into thinking that the idea of nonreductive physicalism as such is not reasonable. However, one could object to this that this small selection of theories is not exhaustive and other existing or not yet existing forms of nonreductive physicalism do not fall victim to the aforementioned criticisms. Indeed, many of the accounts I sketched have been modified in the past decades in order overcome these difficulties. Nevertheless, I think that philosophers should explore other theoretical options beyond nonreductive physicalism, precisely not although, but because nonreductive physicalism has dominated the discussions of the past decades. Even if we cannot show that any nonreductive physicalism is false, it would be wise to put more effort into developing alternative views in the future.

As a prolegomenon to this task, it would be instructive to bethink of the metametaphysical frameworks by which we set the criteria for our respective theory of mind. What I mean by this can be understood by considering the following distinction of different approaches to metaphysics that Peter Strawson introduced in his Individuals: “Descriptive metaphysics is content to describe the actual structure of our thought about the world, revisionary metaphysics is concerned to produce a better structure.” (Strawson 1959, 9) When we assume that metaphysics can be more or less descriptive/revisionary (making it a matter of degree), we can arrange the different metaphysics of mind in a spectrum. Paying attention to our everyday use of concepts, none of the reductive and nonreductive theories we examined in the preceding sections would count as descriptive metaphysics. As for a descriptive metaphysics in this area one would expect a theory that is neither reductive nor physicalist. Accordingly, most of the theories that are discussed nowadays are somewhat revisionary. However, nonreductive physicalism seems to be less revisionary than eliminativism or panpsychism, for instance, which could be a reason why the latter are less popular. Nonetheless, we should not reject more radical revisionary theories out of hand, for example neutral monism (e.g. Westphal 2016). Furthermore, it seems as if Strawson’s own account, which is supposed to be descriptive in nature, has not been given enough attention in recent discussions. In Strawson’s theory ascriptions of mental properties and events always refer to a person. It is because we usually ascribe physical as well as mental properties to persons that there seems to be no need for reduction. Additionally, in contrast to Strawson’s approach, physicalism is a metaphysics that is heavily influenced by and dependent on science.

Consequently, it is not obvious which metaphysical strategy one is to choose. I think, this decision should be based on comparative evaluations of the different approaches relative to certain purposes. However, I could imagine other people having an absolutistic stance to it that allows no relativization in theory choice at this fundamental level.

References

BLOCK, Ned. 1978. “Troubles with Functionalism”. In: Minnesota Studies in the Philosophy of Science 9, 261-325.

DAVIDSON, Donald. 2001¹⁹⁷⁰. “Mental Events”. In: Essays on Actions and Events. Oxford University Press, 207-225.

KIM, Jaegwon. 1992. “Multiple Realization and the Metaphysics of Reduction”. In: Philosophy and Phenomenological Research 52 (1), 1-26.

—— 2011. Philosophy of Mind. Third Edition. Westview Press.

MACDONALD, Cynthia & MACDONALD, Graham. 1986. “Mental Causes and Explanation of Action”. In: The Philosophical Quarterly 36, 145-158.

MELNYK, Andrew. 2008. “Can Physicalism Be Non-Reductive?”. In: Philosophy Compass 3 (6), 1281-1296.

PUTNAM, Hilary. 1967. “Psychological Predicates”. In: W.H. Capitan & D.D. Merrill (eds.): Art, Mind, and Religion. Pittsburgh University Press, 37-48.

SMART, J.J.C. 1959. “Sensations and Brain Processes”. In: The Philosophical Review 68 (2), 141-156.

STRAWSON, Peter. 1959. Individuals: An Essay in Descriptive Metaphysics. Methuen. WESTPHAL, Jonathan. 2016. The Mind-Body Problem. MIT Press.