1.1.1 Substance versus property dualism

The points made in section 1.1 concern the soul and its relationship with its physical body. According to the philosophical view known as soul-body substance dualism, or substance dualism for short, an individual human being is comprised of two substances: a soul and its physical body (‘body’ for short). There is another kind of dualism, what is called property dualism or dual-aspect dualism, which is the view that there is one substance, a body (or brain), that has two kinds of capacities, physical and psychological, where some of the latter are mental in nature. One of the implications of substance, but not property, dualism is the possibility for the soul to exist without its body (exist in a disembodied state) or to be re-embodied in a different body. This entry is primarily concerned with substance dualism, though property dualism will be discussed briefly in section 3 below. As will become evident in section 3, substance dualism is itself a genus of which there are species (creationist and emergentist).

1.1.2 Why be a substance dualist?

The philosopher of cognitive science, Aku Visala, writes that

[t]raditionally, theologians and philosophers in the West have thought that human persons are either identical to or constituted partly by souls […] One of the historically most powerful arguments for the existence of the soul was that a non-natural, non-material entity was the best explanation for our higher-level mental capacities. (Visala 2015: 65)

A couple of pages later, Visala asserts that ‘Christian theological anthropology has tended to affirm a set of common-sense assumptions about the nature of human persons’, which include ‘the claim that we are self-conscious agents who are morally responsible and who retain an identity over the course of [our] earthly lives and even in bodily death and resurrection’ (Visala 2015: 67). While there is no good reason to contest what Visala asserts in these passages, it is important to point out one thing that he fails explicitly to state, which is that the view of ordinary/everyday people (individuals who are not educated philosophically) – what is often referred to as common sense –ß includes the belief that we are souls which are distinct from and have physical bodies. That is, common sense includes the belief in substance dualism. The experimental cognitive scientist Jesse Bering writes that human beings commonsensically (naturally) believe in substance dualism (Bering 2006), and the psychologist Nicholas Humphrey (2011) insists that there is a human inclination to believe in substance dualism. Toward the end of his book Soul Dust, Humphrey mentions other scholars who acknowledge the existence of a natural belief in substance dualism (even though they, like Humphrey, have come to deny the existence of the soul and, thereby, substance dualism):

Thus, development psychologist Paul Bloom aptly describes human beings as ‘natural-born dualists.’ Anthropologist Alfred Gell writes: ‘It seems that ordinary human beings are “natural dualists,” inclined more or less from day one, to believe in some kind of “ghost in the machine” . . .’ Neuropsychologist Paul Broks writes: ‘The separateness of body and mind is a primordial intuition. . . Human beings are natural born soul makers, adept at extracting unobservable minds from the behaviour of observable bodies, including their own.’ (Humphrey 2011: 195)

Even Charles Darwin recognized that ordinary people believe in the truth of substance dualism:

If […] we include under the term ‘religion’ the belief in unseen or spiritual agencies […] this belief seems to be universal with the less civilized races […] As Mr M’Lennan has remarked, ‘Some explanation of the phenomena of life, a man must feign for himself; and to judge from the universality of it, the simplest hypothesis and the first to occur to me, seems to have been that natural phenomena are ascribable to the presence in animals, plants, and things, and in the forces of nature, of such spirits prompting to action as men are conscious they themselves possess.’ (Darwin 1989: Part One, 98)

Why is it natural to believe in the existence of the soul? The short answer is that we are seemingly directly aware of ourselves as psychological substances that are simple in nature in the sense that we are not composed of other substances (see section 3.2), even though we possess a multiplicity of psychological capacities (e.g. the mental capacities already discussed in section 1.1, as well as the qualitative capacities to experience pleasure and pain).

It is important to stress that a belief in the soul’s existence, because of its naturalness or commonsensicality, is not theoretical in nature. That is, a belief in the soul is not an affirmation of the existence of an entity that is theorized and postulated to exist in order to explain something for which we have not been able to find any other plausible explanation. The neuropsychologist Malcolm Jeeves writes that

[s]ome [who affirm the existence of the soul] take a ‘soul-of-the-gaps’ position, much like the older ‘god-of-the-gaps’ position, using the concept of the ‘soul’ to explain those human experiences that we cannot (yet, at least) explain neurologically or biologically. (Jeeves 2004: 245)

Contrary to Jeeves, belief in the existence of the soul as the subject of psychological events (experiences) is commonsensical in nature. It is not arrived at on the basis of a theoretical need to postulate its existence as the locus of experiences for which no neurological or biological subject has been found.

Because many individuals who are interested in the relationship between science and the soul are also interested in the compatibility of beliefs in science and Christianity, it is prudent to take a moment to examine what, if anything, the Bible has to say about substance dualism.

1.2.1 Scriptural support for soul-body dualism

A variety of biblical texts confirms the view that scripture presupposes the natural belief in substance dualism. For example, there is evidence of belief in ghosts of the dead found both in the Hebrew Bible and Christian New Testament. When Saul saw the army of the Philistines, he was afraid and consulted the Witch of Endor whom he asked to bring up from the dead the ghost of the prophet Samuel (1 Sam 28). Saul’s action was in direct violation of the Israelite law not to consult mediums or wizards (Lev 19:31; 20:6; Deut 18:10, 11), a prohibition which on the face of it presupposes the existence of the soul after physical death.

When the disciples of Jesus saw him walking on the sea, they believed they were seeing a ghost (Matt 14:26). In a passage about Jesus’ identity, he asked his disciples ‘Who do people say that I am?’, and he received the response that some thought he was John the Baptist, others believed he was Elijah, while still others thought he was Jeremiah or one of the prophets (Matt 16:13–14). Even Herod, who had John the Baptist beheaded, wondered if Jesus was John (Matt 14:2). The mere suggestion that Jesus might be John the Baptist is interesting because it is reasonable to think the location of John’s body was well known, and it could easily have been verified that his body was still there. What, then, were people, including Herod, thinking? Most plausibly, they thought Jesus was John’s soul re-embodied. The belief of ordinary people in substance dualism also provides the most plausible epistemological backdrop for the conviction of those who knew Jesus that he was casting out unclean spirits from people who were possessed by them (Mark 1:34). And when Jesus stood among his disciples after his resurrection, they were startled and frightened, and supposed they saw a spirit (Luke 24:36–37). As the New Testament scholar Joel B. Green, who rejects substance dualism, writes, ‘It is difficult not to see in the disciples’ responses a [substance] dualist anthropology; accordingly, in their imaginative categories, they were encountering a disembodied spirit, a phantasm’ (Green 2004: 91). Additionally, when Peter arrived at the door of Mary’s house after he had been jailed by Herod, the persons present insisted to a maid, Rhoda, who reported that Peter was at the door, that it could not be Peter but must be his angel (Acts 12:15).

And what about the apostle Paul? A comment of his in his second letter to the Corinthians indicates that he believed in substance dualism. In 2 Cor 12:2–4, he wrote,

I know a person in Christ who fourteen years ago was caught up to the third heaven – whether in the body or out of the body I do not know; God knows. And I know that such a person – whether in the body or out of the body I do not know; God knows – was caught up into Paradise and heard things that are not to be told, that no mortal is permitted to repeat.

The fact that Paul is uncertain about whether this experience was or was not ‘in the body’ makes clear that he believed it was coherent to think that he might have been caught up to the third heaven in a disembodied state (‘out of the body’), which suggests he believed in the existence of the soul and substance dualism. The fact that Paul believed this is not surprising, for two reasons. First, he was largely writing to ordinary human beings, and ordinary human beings believe in substance dualism. Second, Paul was a Pharisee, and as will be made clear below, the Pharisees believed in both the soul’s existence and substance dualism.

The philosopher Kevin Corcoran, who is not a substance dualist, concedes that biblical passages like those cited in the previous two paragraphs support the view that a person is distinct from its body. However, he writes that

to the extent that [such passages] suggest that a person might exist ‘apart from the body,’ it does not follow that the nature of that existence is immaterial or nonbodily […] So, to exist in a state that is ‘away’ from the body does not entail that the state is an immaterial state of an immaterial soul. It could be a bodily state that includes none of the matter that makes up the earthly body. (Corcoran 2006: 145–146)

It would be unreasonable to claim that these texts provide an account of the ontological nature of a self which exists or is capable of existing apart from its physical human body. However, it is reasonable to believe that they presuppose the truth of substance dualism in the broad sense that there are two substances, a physical human body and the self whose body it is, and that the latter is separable from and can exist apart from the former. What a philosopher does is reflect on the natures of the two substances. It is as a result of such reflection that features of the soul, like its simplicity as a substance and complexity in terms of its psychological capacities, are affirmed. But it must be emphasized that while such philosophical reflection enriches our conception of the soul which people like Jesus’ disciples, Herod, and Paul believed is distinct from and can exist apart from a human body or be re-embodied in a different human body, belief in substance dualism is not itself a result of philosophical reflection. The ordinary person naturally believes substance dualism. Thus, it is not surprising to read Corcoran’s recounting of how his mother, upon the death of his father when Corcoran was four, told him that his father was ‘now with God in heaven […M]y mother believed what most Christians have believed down through the centuries, namely, that we human persons are immaterial souls’ (Corcoran 2006: 11, original emphasis).

Anyone who is the least bit familiar with biblical studies will be aware that Christian theologians/philosophers have for two millennia been influenced by the substance-dualist thought of the Greek philosopher Plato (and Platonists more generally). Critics of substance dualism who are also Christians often allege that these theologians/philosophers erroneously read Plato’s ‘Greek’ treatment of substance dualism into the Bible (see Goetz and Taliaferro 2011: Chapter 1 for a detailed description of Plato’s view of the soul, which includes the claims that the soul is immortal [it never came into and will never go out of existence], uncreated, and will, if all goes well for it, survive death forever disembodied). These critics apparently believe that, had these theologians/philosophers not read Plato, they (the theologians/philosophers) would not have found a belief in substance dualism in the Bible, as if to suggest that Plato was the first person to come up with the idea of substance dualism. For example, the theologian Alister McGrath writes that ‘[t]he notion of an immaterial soul was a secular Greek concept, not a biblical notion […] The biblical vision of humanity was that of a single entity, an inseparable psychosomatic unit with many facets or aspects’ (McGrath 2015: 137–138). The New Testament scholar Joel B. Green writes about the post-resurrection appearance of Jesus to his disciples (Luke 24: 36–37) mentioned above that ‘we find no witness to resurrection as escape from bodily existence (as one would expect if a Platonic dualism were presumed here)’ (Green 2004: 92). Green goes on to claim that ‘Jesus [is not] an “immortal soul” free from bodily existence’ and that ‘[r]esurrection is not soul-flight’ (Green 2004: 92, 93). Green’s statements reflect his purpose of showing

that […] an anthropology that posits an ontologically distinct soul, which constitutes the ‘real person’ and which guarantees survival of personal identity from this life to the next, is not only unnecessary but actually stands in tension with key aspects of the resurrection message of the Scriptures. (Green 2004: 86)

Green seemingly believes that, because Jesus possessed a resurrection body, as opposed to being disembodied after death, he (Jesus) was not a soul and substance dualism is false. However, substance dualism per se implies nothing about whether the afterlife will be an embodied (as Christians believe) or disembodied (as Plato thought) existence. Substance dualism is no more, but no less, than the anthropological view that there is a soul which is ontologically distinct from its body, and this view can be true whether the soul is or is not embodied in the afterlife (or is or is not immortal or uncreated). In other words, substance dualism is not, as Green (and McGrath) seems to think, synonymous with Platonic substance dualism. One can believe in the former without believing in the latter. Those concerned about the influence of Platonic dualism on Christian thought seemingly overlook or forget the distinction between an ordinary belief in substance dualism and a philosophical development/treatment of that belief. Because a belief in substance dualism is commonsensical it is found at all points in time and space on the planet earth (e.g. it is found in Hinduism and Buddhism). While Plato philosophized about substance dualism, he did not come up with the idea. Therefore, if one rejects certain aspects of Platonic thought about the soul, one does not undermine the truth of substance dualism per se or the integrity of the biblical authors’ presupposition of it.

N. T. Wright is another biblical scholar who questions the belief in substance dualism in the New Testament (Wright 2016). He emphasizes that the New Testament does not concern itself with philosophical anthropology, and argues that when the New Testament authors do talk about the soul (psyche), it is not as an entity that is distinct from its physical body but as something like the Hebrew nephesh, which he believes is the living, breathing, creature with bodily and psychological properties (the view frequently referred to as Hebrew monism and a version of property dualism, for which see section 3.1). Wright claims that many Christians are unaware of this Hebrew anthropology because they have been influenced, if not blinded, by Greek substance dualism, particularly in its Platonic form where the soul exists disembodied forever after death.

What might a substance dualist say in response to Wright? First, it does not follow from the fact that the New Testament does not concern itself with philosophical anthropology that its authors, who were for the most part Jewish, embraced a Hebrew monistic view of a human being. The Hebrew Bible is no more concerned with philosophical anthropology than is the New Testament. To maintain that it teaches, presupposes, or implies a monistic understanding of a human being runs up against the fact that ordinary people, whether Jewish or non-Jewish, are substance dualists. We get a glimpse of the belief in substance dualism in 1 Samuel 28, which was cited above. Moreover, as Wright himself points out,

[a]ny Jew who believed in resurrection, from Daniel to the Pharisees and beyond, naturally believed in an intermediate state in which some kind of personal identity was guaranteed between physical death and the physical re-embodiment of resurrection. (Wright 2003: 164; cf. Cooper 2000: 101–103)

And as Wright points out elsewhere, one must be careful about using linguistic expressions as the basis for asserting what people believe about the nature of the afterlife. Wright makes clear that just as it is possible to use language about the soul and life after death to refer to the idea of physical resurrection, so also it is possible to use language about physical resurrection to refer to the idea of the soul and life after death. Thus, it is erroneous to conclude from the fact that the Pharisees are consistently described in the Gospels and the Acts of the Apostles and extra-biblical sources as believing in the resurrection of the dead that they did not believe in the existence of the soul that would receive a new body in the future. They did believe in the soul’s existence and its future re-embodiment, as Wright himself notes with the support of various texts (Wright 1992: 320–34).

Second, it should not be forgotten that the apostle Paul was a Pharisee. That he believed, like other Pharisees, in the possibility of disembodiment is evidenced in 2 Cor 12:1–4, which was cited above. Wright says the following about this passage:

[Paul] never suggests that, if he wasn’t embodied, it was his psyche which made the journey [to the third heaven]. The fact that he is uncertain about whether this experience was or wasn’t ‘in the body’ indicates that, for him, it wouldn’t have been problematic if the body had been involved. For him, the body could just as well have been carried up to heaven […] Equally, of course, that fact that he can consider the possibility that the experience might not have been ‘in the body’ does indeed indicate that he can contemplate non-bodily experiences, but […] I don’t think one can straightforwardly argue from this to what is now meant, in philosophical circles, by ‘dualism’. (Wright 2016: 6–7, original emphasis)

A substance dualist will likely respond that one need not argue from this passage to substance dualism. The fact that Paul can ‘indeed contemplate non-bodily experiences’, experiences had without a body, indicates that he presupposes commonsensical substance dualism. Wright seems to believe that the ‘dualism’ of philosophical circles is Platonic in form. One certainly cannot, as Wright says, straightforwardly argue from what Paul says in 2 Cor 12:1–4 to the conclusion that he believed in Platonic dualism. But, again, substance dualism and Platonic dualism are not the same thing. The latter is a species of the former, and a rejection of the species is not sufficient for a rejection of the genus.

The criticisms of biblical scholars and theologians of substance dualism examined in this sub-section reflect a belief held by many professional philosophers and scientists that substance dualism is false. The explanations given for this belief are typically that developments in neuroscience and the methodology of science as a whole support the falsity of substance dualism (see Theology and Neuroscience). Section 2 is concerned with these issues.

2.2.1 Universal versus localized methodological causal closure

What is the reasoning that supposedly supports an affirmation of the methodological causal closure of the physical world? Consider the following comments of the philosopher Jaegwon Kim:

You want [or choose] to raise your arm, and your arm goes up. Presumably, nerve impulses reaching appropriate muscles in your arm made those muscles contract, and that’s how the arm went up. And these nerve signals presumably originated in the activation of certain neurons in your brain. What caused those neurons to fire? We now have a quite detailed understanding of the process that leads to the firing of a neuron, in terms of complex electrochemical processes involving ions in the fluid inside and outside a neuron, differences in voltage across cell membranes, and so forth. All in all we seem to have a pretty good picture of the processes at this microlevel on the basis of the known laws of physics, chemistry, and biology. (Kim 1996: 131–132)

According to Kim, the physical explanatory story is unproblematic until one introduces an immaterial mind (a soul) to explain the raising of one’s arm:

If the immaterial mind is going to cause a neuron to emit a signal (or prevent it from doing so), it must somehow intervene in these electrochemical processes. But how could that happen? At the very interface between the mental and the physical where direct and unmediated mind-body interaction takes place, the nonphysical mind must somehow influence the state of some molecules, perhaps by electrically charging them or nudging them this way or that way. Is this really conceivable? Surely the working neuroscientist does not believe that to have a complete understanding of these complex processes she needs to include in her account the workings of immaterial souls and how they influence the molecular processes involved […] Even if the idea of a soul’s influencing the motion of a molecule […] were coherent, the postulation of such a causal agent would seem neither necessary nor helpful in understanding why and how our limbs move […] Most physicalists [those who believe all of reality is physical in nature…] accept the causal closure of the physical not only as a fundamental metaphysical doctrine but as an indispensable methodological presupposition of the physical sciences […] If the causal closure of the physical domain is to be respected, it seems prima facie that mental causation must be ruled out. (Kim 1996: 132, 147–148)

A believer in substance dualism and soul-to-body causal interaction (i.e. an ordinary person) will express surprise at Kim’s remark that reference to a soul seems neither necessary nor helpful in understanding why and how our limbs move on certain occasions. Surely if, as the substance dualist believes, the soul is what chooses to act for purposes, then reference to it seems absolutely necessary and helpful for understanding why certain movements of human bodies occur. For example, when an author chooses to accept an invitation to write an entry for an encyclopaedia and proceeds to move his fingers in specific ways on a keyboard to type the entry, his purpose for writing the entry teleologically explains (see section 1.1) that choice and the subsequent finger movements which he, as a soul, causally produces for the fulfilment of that purpose.

What, then, might the substance dualist say in response to Kim’s argument that a neuroscientist must, in accordance with the methodological principle of causal closure, exclude any appeal to souls to explain physical bodily movements? The substance dualist can draw a distinction between a neuroscientist as an ordinary human being and a neuroscientist as a physical scientist. Given this distinction, the substance dualist can maintain that a neuroscientist as an ordinary human being can invoke a purpose to explain the relevant movements of an author’s fingers in writing an encyclopaedia entry where those movements are ultimately caused by a soul acting for that purpose. And invoking this explanation is thoroughly consistent with a neuroscientist’s methodologically excluding in principle such explanations in the context of his work as a neuroscientist.

How can the distinction between a neuroscientist (or any scientist) as an ordinary human being and as a scientist be justified? To begin to answer this question, consider the following statement from the pen of the twentieth-century British geneticist, J. B. S. Haldane: ‘when I set up an experiment I assume that no god, angel, or devil is going to interfere with its course’ (quoted in Subramanian 2020: 9). Two points are relevant. First, were Haldane to have believed that the mental-to-physical causation involved in soul-body causal interaction was in principle impossible (inconceivable, as Kim claims), then he would not have needed to make the stated assumption (which concedes the possibility of soul-body causal interaction but excludes it in experimental scientific work). Second, it is possible to distinguish between local and universal causal closure. While a scientist must assume the causal closure of the physical world, he does so only in the limited context of his experimental work. He need not assume that the physical world is closed at all points in time and space. In other words, while Haldane, in trying to ascertain how physical objects causally interact, was justified in assuming that no god, angel, devil, or soul was interfering with that part of the physical world with which he was concerned in his experimental work, this limited assumption in no way required the broader assumption that the entire physical world was closed at every point in space and every point in time.

The substance dualist will make clear that proponents of the argument from causal closure regularly fail to make this local-universal distinction. For example, when the philosopher John Heil presents the methodological argument from causal closure against soul-body causal interaction he assumes that the closure required must be universal in scope: ‘Modern science is premised on the assumption that the material universe is a causally closed system: every event in the material universe is caused by some other material event (if it is caused by any event)’ (Heil 2020: 25, original emphasis). But why think modern science is methodologically premised on the assumption that the material universe in its entirety is a causally closed system?

But, Heil might retort, if a scientist needs to assume limited causal closure, why not think it is reasonable to view this assumption as shorthand for a requisite assumption that is universal in scope? In other words, why not think the argumentative burden is on the substance dualist to explain why the assumption of limited causal closure is not an abbreviation of that which is most general in nature?

At this point, the substance dualist will likely respond that the explanation for why it is not reasonable to understand the assumption of limited causal closure as shorthand for what is universal in nature is because we are aware of reasoning and choosing to act for purposes, where these mental events seemingly produce effects in the physical world (thus falsifying universal causal closure). Given this is the case, it is reasonable to seek to understand how what happens in our mental lives with their physical effects is compatible with the methodology of science. The distinction between limited as opposed to universal causal closure achieves this compatibility.

Given that the assumption of limited, and not universal, causal closure can be methodologically justified, what is it that a physical scientist is attempting to discover about physical objects in his experimental work? In the case of Kim’s neuroscientist, she is attempting to discover the capacities of particles or micro-entities such as neurons to be causally affected by exercised causal capacities of other physical entities, including other neurons. For example, in his pioneering studies of the brain, the brain scientist Wilder Penfield caused movements of limbs of his patients by stimulating the cortical motor areas of their brains with an electrode (Penfield 1975). As Penfield observed the neural impulses caused by the stimulation from the electrode, he had to assume that during his experiments the areas of the brains of his patients were causally closed to other causal influences. Without this methodological assumption, Penfield could not reasonably conclude that it was both (i) the electrode, as opposed to something behind the scene and empirically undetectable such as the soul of the patient or someone else or, in Haldane’s words, a ‘god, angel, or devil’, that was causally affecting the capacities of the neurons to conduct electrical impulses, and (ii) the causal impulses of those neurons that causally affected the same capacities of other neurons further down the causal chain, which resulted in the movements of the limbs. However, there was no reason for Penfield to think that, because his scientific work required the methodological assumption of causal closure in the areas of the brain and body which he was investigating during his experiments, that he also had to be committed, as a scientist, to the assumption that the material universe is universally causally closed so that at other times (times when he was not conducting his scientific work) the relevant brain (neural) events could only be caused by other physical events and not by the soul of the patient (or some other being).

In other words, it does not follow from the fact that, because Penfield or other neuroscientists must methodologically assume causal closure of a delimited area of the brain (body) in the context of their experimental work in order to ascertain how physical entities causally interact, they must be committed as scientists to the universal explanatory exclusion of mental events of souls that on certain occasions cause the occurrence of neural events in their brains. If neuroscientists assume universal causal closure, they do not do so as scientists but as individuals with an independent philosophical commitment which excludes the causal efficacy of souls.

If the foregoing reasoning is sound, then scientists can reasonably remain ordinary human beings who are open to the causal efficacy of souls on brains on certain occasions. But on which occasions? The obvious answer is, as has already been suggested, on occasions when souls are reasoning and purposefully choosing to act and carrying out their choices. The purposeful typing of an encyclopaedia entry is an example of one such occasion (as is the occasion when Penfield purposefully stimulated a patient’s brain with an electrode). It is reasonable for a writer to assume that when he chooses to type his entry and his fingers move in accordance with the purpose for which he is typing that his choice (or some other mental event correlated with his choice) is directly causing the relevant brain (neural) events and indirectly producing the movements of his fingers that are effects of those brain events. It is unreasonable to think that every time an author purposefully chooses to type an encyclopaedia entry, or do anything else, physical causes alone purposelessly occur to produce the very movements of his fingers that are required to type his written work. Such a coincidence would truly be miraculous.

However, what if there are sometimes undetermined (uncaused) events in micro-entities? What if on occasion a neuron fires without any cause whatsoever? If it is assumed that neurons occasionally do fire in this way, is it possible to distinguish between those firings that occur without any physical cause and those that occur as the result of being causally determined solely by a mental event in a soul? After all, the two firings are alike to the extent that both lack a physical cause. Do they differ in a relevant way?

It is possible to distinguish between these two firings by remembering that the relevant mental causal event in a soul is an action (or a mental event correlated with that action) that has an explanation in the form of a purpose. How plausible is it to maintain that every time a soul makes a choice to write for a purpose that the relevant uncaused neural events which lead to the purposefully chosen finger movements just happen to occur without any cause? Such repeated coincidences would again be miraculous. It is far more reasonable to maintain that, while those neural firings lack any physical cause, they are caused by the relevant purposeful mental event.

2.2.2 An alleged problem for soul-body causal interaction

Soul-to-body causal interaction requires the occurrence of physical events that lack physical causes. It is therefore important to emphasize that the belief in the soul’s existence and causal activity is not the result of a failure to find a physical cause for a physical event (e.g. a neural firing). That is, the belief in the existence of the soul and its causal activity is not arrived at in light of a failure to find a physical cause for the relevant physical event. That would be an appeal to a soul-of-the-gaps explanation. The situation is the reverse. On the occasions when a person is aware of choosing purposefully to perform an action, such as writing an encyclopaedia entry, it must be the case (absent ‘miraculous’ coincidences) that there is some initial physical event (neural firing) which is not caused by another physical event but by a mental event which has a purposeful explanation. In other words, it is not that gaps in the physical causal story lead to belief in the soul, but that belief in the soul and purposeful mental causes leads to the belief that there must be gaps in the physical causal story.

2.2.3 A hierarchical/layered view of reality and methodological causal closure

According to the philosopher John Heil,

[t]he universe contains levels or layers of objects and properties governed by successive levels of causal laws. Although objects at higher levels are often enough made up of objects at lower levels, it is nevertheless true that higher-level objects and their properties have lives of their own. They are not reducible to, not ‘nothing but’, arrangements of objects and properties at lower levels. (Heil 2020: 123)

Heil maintains that laws at the higher levels hold only ceteris paribus or ‘other things being equal’. For example, assume it is a law that if a soul, S, wants x and believes y is needed to obtain x, then S wants and will act to obtain y. Thus, if S desires to take the subway and believes a ticket is necessary to do so, then S will want and act to obtain a ticket. S will want and act to obtain a ticket, says Heil, unless S believes he has no money, which might lead to his losing his desire to ride the subway, or S is hit by a piece of falling plaster and knocked unconscious, etc. According to Heil, the laws of biology and chemistry – though lower in the hierarchy of laws than psychological laws – are similar to those found in psychology in the sense that they are ceteris paribus in nature. However, writes Heil, ‘[t]he laws governing the basic entities [the lowest-level laws] studied in physics […] are exceptionless [non-ceteris paribus]’ (Heil 2020: 123).

What Heil never explains is why the lowest-level laws are (must be) exceptionless. Why could they not be ceteris paribus in nature, such that physical event y will occur under condition C given the occurrence of physical event x, unless some other event such as a choice by soul S for a purpose intervenes to prevent the occurrence of y? Why think a soul could not intervene in this way? After all, a soul is, by hypothesis, a simple entity with capacities. As a simple entity, it is ontologically akin to the lowest-level physical entities with their capacities. Does science’s methodological commitment to the causal closure of the physical world exclude causal intervention by a soul at the level of basic entities? If the argument of section 2.2.1 is sound, then the answer is ‘no’. The causal closure (as opposed to the methodological assumption of the causal closure) of the physical world? If Heil were to respond that the physical world is causally closed, then one could ask what justifies the claim that this is the case. In lieu of an answer, Heil might simply assert that he has no reason for believing that the physical world is causally closed. He just believes that it is. There is nothing in principle philosophically suspect about a person having a belief that is not justified in terms of one or more other beliefs. All of us have beliefs of this kind, what philosophers think of as basic beliefs. Basic beliefs are not uncaused or freely chosen. For example, a basic belief that the stove top is hot might be caused by an awareness of the heat one experiences while standing before the stove. Similarly, a basic belief that one is happy might be caused by one’s awareness of one’s experiences of pleasure. Were Heil to maintain that his awareness of the physical world or some property of the physical world causes him to believe the physical world is causally closed, then he would have a basic belief that is not shared by the substance dualist. At this point, there would be no epistemic higher court of appeal. There would be an irresolvable difference in basic beliefs.

2.2.4 The non-spatiality of the soul and methodological causal closure

In the history of thought about the soul, the issue of its location has received serious attention. Is the soul located in space? It certainly seems that it is. For example, René Descartes wrote that ‘I imagined [the soul] to be something tenuous, like a wind or fire or ether, which permeated my more solid parts’ (Descartes 1984: 17). Philosophers writing about the nature of the soul, like Augustine and Aquinas, affirmed that the soul is present in its entirety in every point of space occupied by its physical body because, as Descartes’ comment suggests, it seems to us that we fill the space occupied by our physical body (see Goetz and Taliaferro 2011: 43–45, 51–53). However, Descartes, for reasons that need not be reviewed here, apparently denied that the soul is present in space at all (see Goetz and Taliaferro 2011: 70–76).

When one reads philosophical treatments of substance dualism, one regularly encounters the objection that it is unintelligible how a non-spatial substance can causally interact with one that is spatial (see Sosa 1984; Kim 1996; Taylor 1992). However, what should be remembered is that the objection to substance dualism from methodological causal closure essentially has nothing to do with whether a soul is spatially located. Even if a soul is located in space (say, in the space of its physical body), the objection from methodological causal closure is that there is no explanatory room for mental causes of physical events, even when the mental events involved in those causal explanations occur in spatially localized souls.