Christian Physicalism and Personal Identity
Human persons undergo many changes throughout their lives. In fact, each phase of life, from birth and adolescence to adulthood and old age, has its own kind of change associated with it. Despite all of these and other changes, it is a commonly held view that a person remains the same individual person throughout his or her life. Explaining how this is possible, if indeed it is, has proven very difficult and constitutes what philosophers call the problem of personal identity.
This problem is even more challenging for Christians because they hold, as an essential part of their faith, that it is possible for a person to share life with God after death.1 Accordingly, Christian philosophers must try to give an account of how a person in the afterlife can be the same individual person who once lived on the planet earth. One popular solution to this problem is to hold that a human being has a nonphysical soul that can survive the death of the body.
However, the view that humans have a nonphysical soul that survives the death of the body has come under significant attack in recent centuries. This is due, primarily, to two revolutions in science. The first revolution came from Charles Darwin. His theory of evolution, though he did not use that word, raised serious questions about the origin and nature of human beings. If humans evolved from non-human animals it would seem that the difference between humans and other animals is merely a matter of degree. In addition, if life itself emerged from non-living matter, as some scientists have hypothesized, then appealing to a nonphysical soul would seem to be superfluous. This view appears to be reinforced by the second and currently occurring revolution, which comes from neuroscience. Thanks to new discoveries about the brain, scientists seem to be able to explain more and more of the functions that were once attributed to the soul.
In the wake of these developments some Christians have advocated what can be called Christian physicalism. For example, Nancey Murphy, in her book Bodies and Souls, or Spirited Bodies?, says the following: â€œMy central thesis is, first, that we are our bodies â€“ there is no additional metaphysical element such as a mind or soul or spirit. But, second, this â€˜physicalistâ€™ position need not deny that we are intelligent, moral, and spiritual.â€2 Instead of focusing on Murphyâ€™s entire project in this paper, I have chosen to investigate the implications that her understanding of Christian physicalism has for personal identity. Ultimately, I will argue that her view can neither account for personal identity in this life nor explain how a person in the afterlife can be the same individual person who once lived on the planet earth. Before I can argue these points, we need to examine the problem of personal identity in greater detail.
I. Identity and Personal Identity
Any attempt to solve the problem of personal identity requires a more general account of identity. Unfortunately, I do not have enough space here to present and defend such an account. Nevertheless, I must explain briefly some of the terminology that I will use and clarify some of the pertinent issues. With this in mind, let me say that I understand identity, which I use interchangeably with sameness, as lack of difference. I understand difference broadly enough to cover any case where X is not Y.
The problem of personal identity is not the problem of absolute identity, because, as I mentioned earlier, all humans undergo change during their lives. Therefore the problem of personal identity is a type of relative identity problem. A general formula for relative identity is the following: X and Y are identical with respect to P, where P excludes some characteristic or characteristics of X and Y. In this case P stands for personhood. Of course, we need some understanding of what a person is for this formula to be useful. Since Murphy wants to defend a view of persons that is compatible with Christianity, I suggest that we understand a person to be a rational being that is capable of making free choices.
But even this is not enough to adequately characterize the problem of personal identity. Socrates and Plato were both identical with respect to this understanding of personhood, but they were not the same individual person. Therefore individuality is also part of the problem of personal identity. I agree with Jorge J. E. Gracia that the proper understanding of individuality is noninstantiability.3 Conversely, the proper understanding of universality is instantiability. For example, human, which is a universal, can be instantiated in Socrates. However, Socrates, the individual who taught Plato, is noninstantiable.
Combining all of these insights, we can say that the problem of personal identity involves one individual remaining the same with respect to personhood through change. We can represent this with the following formula: X at time one and Y at time two are the same person if and only if X and Y are the same with respect to personhood and X and Y are the same individual. In order to make use of this formula, we need to know the necessary and sufficient conditions for X and Y to be the same individual. These are as follows: X and Y are the same individual if and only if X and Y have the same numerical principle of individuation. By principle of individuation I mean that which makes a thing individual. For example, some philosophers have argued that spatio-temporal location is the principle of individuation. These philosophers hold that Socrates and Plato are not the same individual because Socrates and Plato cannot occupy the same space at the same time. Because Socrates and Plato cannot occupy the same space at the same time, what individuates Socrates is numerically distinct from what individuates Plato. Therefore Socrates and Plato are numerically distinct individuals.
I could say more about the problem of personal identity, but I have clarified it enough for our purposes here. We are now ready to examine Murphyâ€™s Christian Physicalism in order to determine whether it can account for personal identity. I will examine her notion of personhood first because if that is found to be unsatisfactory then her account of personal identity will be unsatisfactory as well.
II. Persons and Nonreductive Physicalism
Murphy prefers to call her position â€œnonreductive physicalism.â€4 She explains that the word physicalism indicates her â€œagreement with the scientists and philosophers who hold that it is not necessary to postulate a second metaphysical entity, the soul or mind, to account for human capacities and distinctiveness.â€5 It is clear, then, that with respect to human beings, she is rejecting dualism and endorsing a kind of material monism. Indeed, Murphy admits that she could have called her position â€œnonreductive materialism.â€6 However, the word materialism has atheistic connotations that she wanted to avoid. By the way, I should note that her material monism extends to everything except God: â€œChristians need two basic metaphysical categories: God and creation. The claim that Godâ€™s creation is purely physical does not entail that there is no (nonphysical) creator.â€7
The word nonreductive in â€œnonreductive physicalismâ€ serves to distinguish her position from reductive physicalism. Both positions hold that a human being is purely physical, but reductive physicalism also entails causal reductionism. Causal reductionism is the view that the behavior of a complex entity, such as a human being, is determined by the laws governing its parts. Because the parts govern the whole, Murphy calls this â€œbottom-up causation.â€8 The problem with causal reductionism is that it is incompatible with traditional conceptions of personhood, and with Christian theology, because it precludes freedom and moral responsibility.9 As she explains, â€œ[I]f mental events can be reduced to brain events, and the brain events are governed by the laws of neurology (and ultimately by the laws of physics), then in what sense can we say that humans have free will? Are not â€¦ their willed actions merely the product of blind forces?â€10
To overcome this problem, Murphy must defend a view that does not entail causal reductionism. Since she cannot appeal to a nonphysical soul, she is left with only one option. She must hold that entities with new causal powers can emerge when matter is properly organized. These new powers exert, what she calls, â€œtop-down or downward causation.â€11 To explain the distinction between bottom-up and downward causation she gives several examples.
Her first example is a paper airplane. The fact that the mass and rigidity of the paper airplane comes from the atoms that comprise it is an example of bottom-up causation. The fact that the behavior of the paper airplane is almost entirely governed by its shape (a holistic property) and environmental factors is an example of downward causation. She uses this example to refute the claim that â€œthe behavior of an entity is determined by the laws governing the behavior of its parts.â€12
Her second example is a jet airplane that is on auto-pilot. The jet will react to incoming data and change its course accordingly. Unlike the paper airplane, it is self-directed. And unlike the laws of nature that affect the jet at the level of its parts, such as gravity, the self-movement of the jet airplane operates under its own, different laws. She uses this example to make the following point:
[I]t is possible to design a system that uses information about its own states and about its environment in such a way as to alter its own behavior in pursuit of a goal. Once such systems have come into existence, new regularities, new laws of nature, come into existence with them. The basic laws of physics are not violated in such cases, and in fact it is the reliable working of the basic laws of physics that makes the design and operation of such systems possible.13
Murphy also discusses the emergence of other systems, such as language. She argues that language allows allow us â€œto represent to ourselves and pursue abstract goals.â€14 This, she says, is one of the keys to overcoming biological determinism.15 It is not difficult to see where Murphy is going. For her, a human person is nothing other than a collection of higher-level processes and systems that emerge sometime in childhood from the parts of the body. Since the collection exercises downward causation the behavior of the whole is not reducible to the behavior of the parts of the body.
Is Murphy correct? Can nonreductive physicalism account for freedom and moral responsibility? So far, I am not convinced. In addition, I question whether nonreductive physicalism can account for the emergence of consciousness. I should point out that even other physicalists, such Jaegwon Kim, have admitted that the problems of mental causation and consciousness â€œrepresent the most profound challenge to physicalism.â€16 Accordingly, I think it is important to examine these two problems a little more closely. Let us begin with the problem of freedom and moral responsibility since Murphy has identified this as the main worry for a physicalist anthropology.
A. Freedom and Moral Responsibility
Murphy thinks she can avoid causal reductionism by keeping determinism on the lower level but not on the higher level. Speaking of the threat of neurobiological determinism to human freedom, she says:
The issue is not whether neurobiological processes are themselves determinate, but whether neurobiological reductionism is true. If I have made the case for the intelligibility of downward causation and its prevalence in shaping and reshaping the neural system, then the determinism of the laws of neurobiology is actually not relevant to the issue of free will. With an account of downward causation via selection, it makes no difference whether the laws of the bottom level are deterministic or not; higher-level selective processes can operate equally well on a range of possibilities that have been produced (at the lower level) by either random or deterministic processes.17
Is this understanding of top-down causation good enough to account for freedom and moral responsibility? Several philosophers have expressed doubts.18 For example, William Hasker has said that her use of the word selection is misleading because it suggests â€œthat there is some higher-level entity exercising intentional control in the situation.â€19 Stewart Goetz has made a similar point: â€œI cannot be morally responsible for a choice that I was determined to make, regardless of whether that choice was bottom-up or top-down determined.â€20 Indeed, Murphy admits that some of the higher-level entities will be deterministic.21 If all of them are deterministic then human freedom and moral responsibility do not exist. Her only hope is that some of the higher-level processes are not deterministic. But what evidence do we have of that?
Murphy thinks there is empirical evidence: â€œIf we give up the assumption that the behavior of all higher-level entities must be deterministic, and simply look, we see that there are also complex systems (e.g. organisms) that have emerged from (largely determinate) lower levels and that do not behave in regular (deterministic) ways.â€22
But is it not true that the reason why these organisms act in a non-determinate way could be due to a nonphysical cause? The only way to use these examples to defend her position is to assume that these organisms emerged from purely physical causes. But this is equivalent to assuming nonreductive physicalism and thus her argument is circular.
Even so, I think there is a deeper metaphysical problem here. Specifically, I do not think Murphy has enough metaphysical furniture to be able to account for non-deterministic downward causation. As a physicalist, she cannot appeal a nonphysical soul to explain human freedom. Instead, she must say that an entity capable of free choice and moral responsibility emerges, ultimately, from complex arrangements of microphysical parts. But the microphysical world is a world of determinism (making allowance for quantum indeterminacy, of course). The result is that, metaphysically speaking, Murphy is forced to accept a compatibilist understanding of human freedom. Although she says â€œthe compatibilist-incompatibilist debate is misguided,â€ she also says â€œIt is difficult to conceive of an action whose causal etiology involves no biological factors or social determinants.â€23 It is this last point that precludes libertarian views of freedom, which have been very popular among Christians.
For example, Eleonore Stump, while discussing the libertarianism of St. Thomas Aquinas, says that if â€œthe chain of causation eventuating in a human action … [could] be traceable ultimately to something outside the agent…. [that would be] fatal to Aquinasâ€™s theory of free will since on Aquinasâ€™s theory nothing outside the agent exercises efficient causality on the will.â€24 In order for Aquinas to escape the determinism of the microworld, he must appeal to something that is higher, ontologically speaking. He can do this because for him the soul is nonphysical and thus not subject to the determinism of the microworld. Consequently, the nonphysical soul allows a person to exercise downward efficient causation on the body.
Murphy tries to make a similar move. Like Aquinas, she correctly appeals to a higher-level entity, to avoid the determinism of the lower level. However, unlike Aquinas, Murphyâ€™s higher-level entities and lower-level entities only differ in degree (i.e., in arrangement and complexity). If the new causal powers of the higher-level entities only differ in degree from the behavior of the lower-level entities, I do not think that is good enough to account for freedom and moral responsibility. Conversely, if the new causal powers differ qualitatively from the behavior of the lower-level entities, that leads to a metaphysical problem.
The problem is this: How can powers that are qualitatively different emerge from entities that are only quantitatively different? Kevin Corcoran has made a similar point: â€œabsent some sort of robust emergent power or even a substance emergence view of the mind, it is hard to see how to escape microdeterminism.â€25 This raises the next problem I want to discuss, namely, the problem of emergence itself.
B. The Emergence of Life, Consciousness, and Intelligence
In order to account for a conception of personhood compatible with traditional views, and with Christianity, nonreductive physicalism must be able to account for the emergence of life, consciousness, and intelligence. These are big metaphysical problems, and, unfortunately, I cannot treat them here in the depth that they deserve. However, I want to discuss one of them, namely, the emergence of consciousness.
Murphyâ€™s understanding of emergence differs from other philosophers and it is important to clarify the difference. For example, Hasker, who calls his view â€œemergent dualism,â€ holds that the mind emerges from matter but that it is â€œnot composed of physical stuff.â€26 Murphy explicitly rejects this kind of emergence: â€œThe difference between Haskerâ€™s view and mine, then, is that I am satisfied with asserting, in the case of human beings, the emergence of new causal powers. I would argue that he has simply gone too far (further than one needs to go and further than his arguments warrant) in postulating the mind or soul as an emergent entity.â€27
If consciousness is only a new power of a purely physical being, as the above excerpt suggests, then Murphy is committed to the view that consciousness emerges when atoms are organized in the proper way. But is this possible? Consciousness appears to be something that is radically different from other properties of matter. The shape of an airplane (a higher-level structure) can easily be formed by arranging atoms (lower-level parts). Indeed, both the parts and the whole occupy a certain region of space. However, it does not appear that an arrangement of atoms could lead to something as radically different as consciousness. Other philosophers have noted the enormity of the problem. For example, Jerry Fodor has said: â€œNobody has the slightest idea how anything material could be conscious. Nobody even knows what it would be like to have the slightest idea about how anything material could be conscious.â€28 In addition, David J. Chalmers has argued at length that consciousness cannot be explained by reductive or materialist accounts.29
I would like to give a brief argument to show why I am pessimistic about the ability of nonreductive physicalism to account for the emergence of consciousness. If it is agreed that consciousness is a property that is radically different from the other properties of matter, then we cannot claim it emerges from matter. This is because, in such a case, the effect would be greater than the cause and that would violate a fundamental metaphysical principle and, ultimately, undermine science.30 Murphy cannot reduce consciousness to matter because she is committed to nonreductive physicalism. Thus the only option she has left is to greatly enhance her conception of matter so that matter contains within it the potential to become conscious if it is properly organized. I would also argue that similar enhancements must be made with respect to life and intelligence. The result of all of these enhancements is something that resembles spirit more than it does matter, and thus her overall view would be closer to spiritual monism than to material monism.
Thus, in the end, it seems nonreductive physicalism cannot account for freedom and moral responsibility or for the emergence of life, consciousness, and intelligence. Moreover, even if these problems did not exist, I still do not think Murphyâ€™s view can account for personality identity. In order to understand why, we need to examine her view more closely.
III. Personal Identity and Nonreductive Physicalism
Near the end of her book Bodies and Souls, or Spirited Bodies?, Murphy gives an outline of a nonreductive physicalist account of personal identity.31 As I mentioned earlier, there are two problems for Christians. The first problem is accounting for personal identity during the course of oneâ€™s earthly life, for example, from childhood to old age. The second problem is accounting for how a person in the afterlife can be the same individual person who once lived on the planet earth. I will argue that her view cannot account for personal identity in either case. Before I explain why, I think it will be helpful to examine, briefly, the advantages of a nonphysicalist account of personal identity.
In the history of Roman Catholicism, for example, the nonphysical soul was held to be either a separate substance, as in the case of St. Augustine, or subsistent, as in the case of Aquinas.32 As such, the soul of Peter, for example, continued to exist and remain the same despite changes to his body. Even though Peterâ€™s soul would also undergo changes during his life, for example acquiring new moral habits, these were merely accidental changes, not substantial changes. After physical death, Peterâ€™s soul continued to exist and, in the case of Aquinas, it was later joined to a glorified body.33
It is difficult to overstate the advantages that the above nonphysicalist accounts have for Christians with respect to personal identity. Nevertheless, Murphy has claimed that â€œChristians have nothing to lose and much to gain from recognizing our kinship with the rest of physical creation.â€34 Let us see if that is the case.
Earlier, I argued that the problem of personal identity involves one individual remaining the same with respect to personhood through change. I gave the following formula: X at time one and Y at time two are the same person if and only if X and Y are the same with respect to personhood and X and Y are the same individual. Accordingly, there are two ways that X and Y could fail to be the same individual person. First, X and Y could differ with respect to personhood. Murphy agrees with this point: â€œin discussing personal identity it is necessary to ask specifically what are the identity criteria for the covering concept person.â€35 Second, X and Y could be different individuals. Murphy raises this point when she discusses the distinction between numerical identity and qualitative identity.36 Accordingly, a satisfactory account of personal identity must be able to preserve both individuality and personhood over time. Let us, then, examine these separately by considering some best case scenarios.
In the first scenario we will preserve the individuality of a person named John. As we have seen above, a human person is a collection of higher-level processes and systems that emerge sometime in childhood from the parts of the body. Indeed, Murphy says that â€œIt is not the body qua material object that constitutes our identities, but rather the higher capacities that it enables.â€37 Over the next ten pages she argues that many criteria are necessary for personal identity, including: memory, consciousness, moral character, dispositions, habits, and practices.38 She also says that without a body these personal attributes could not exist.39
So, for sake of argument, let us suppose that from the age of twenty to the age of forty every single atom of Johnâ€™s body remained with him. In other words, he did not eat and assimilate any food; he did not lose any weight, and so forth. However, let us suppose that his atoms could change some of their arrangements, so that he could experience new sights and sounds, think about them, and change his mind on various issues.
Even in this unrealistic scenario John will not remain the same person for very long. This is because most, if not all, of the criteria that Murphy has listed as necessary to personal identity will have changed. Over the twenty years John will gain new memories (and perhaps lose some). In addition, he will pick up new habits (and perhaps lose some). He might have pristine moral character in the beginning, and then become a vile scoundrel towards the end, and so on. The point is that the collection of higher-level systems that is John is constantly changing and thus cannot account for his personal identity over time.
Let us consider another best case scenario but this time we will preserve Johnâ€™s personhood but not his individuality. Imagine over a twenty year period that John did not gain or lose any memories, or moral habits, and so on. However, over that time all of the atoms of his body were replaced by new atoms such that not even one atom at time one (when he was twenty years old) remained with him at time two (when he is forty years old). In this scenario, John at time one and John at time two would be the same with respect to personhood but John at time one would be a numerically distinct individual from John at time two because all of the atoms are different.
It might be objected that I should use Johnâ€™s bundle of features (i.e., his memories, his habits, etc.), instead of his atoms, to individuate him. Indeed, Murphy claims that â€œmaterial objects can retain their identity over time despite change in the material of which they are composed.â€40 However, this will not work for at least two reasons.
First, although using the bundle might seem to work in this unrealistic scenario, it would not work in a real life setting. In a real life setting Johnâ€™s bundle of features is certain to change, and if the bundle individuated him then he would not remain the same individual person for very long. Second, in order to individuate him, Johnâ€™s bundle of features would have to make him noninstantiable. However, Murphy holds just the opposite. In order to account for how a person in the afterlife can be the same individual person who lived on the planet earth, Murphy holds that Johnâ€™s bundle of features can instantiated into a glorified body:
[A]ll of the personal characteristics as we know them in this [earthly] life are supported by bodily characteristics and capacities and these bodily capacities happen to belong to a spatio-temporally continuous material object, but there is no reason in principle why a body that is numerically distinct but similar in all relevant respects could not support the same personal characteristics.41
This has the unfortunate result of turning John into a universalâ€”something that can be instantiated into different bodies. It also leads to other problems.
In the above scenarios I treated identity of personhood and identity of individuality separately. However, Gracia has argued, that â€œ[t]he principle of identity must be individual of itself and unchanging in order to account for numerical sameness through time.â€42 Unfortunately, Murphy cannot appeal to one principle to account for both identity and individuality. As we have seen, Johnâ€™s bundle of features cannot individuate him and, because the bundle is constantly changing throughout his life, it cannot account for personal identity over time. Similarly, the atoms that compose Johnâ€™s body are constantly being replaced with different atoms and therefore John does not remain the same individual person over time.
Finally, there is another problem. Gracia has argued that the principle of individuation is existence.43 Suppose, then, that during Johnâ€™s earthly life, God made three replicas of him and infused his bundle of features into each one. Since each replica has its own distinct existence, each replica would be a different individual from John. This also explains why a replica of John in the afterlife would not be John, but a different individual. Murphy holds that a personâ€™s attributes are dependent on a body for their existence. When that body dies the attributes pass out of existence. If existence is the principle of individuation then once John passes out of existence he is gone forever. Even if, in Heaven, God brought into existence a replica of John, the replica, because it has a new and thus a distinct act of existence, would be a different individual.
Thus, in the final analysis, it turns out that nonreductive physicalism is not a very attractive position for Christians. This is because it puts out of reach the hope of all Christians, to share life forever with God.44
5 Nancey Murphy, â€œHuman Nature: Historical, Scientific, and Religious Issues,â€ What Happened to the Soul: Scientific and Theological Portraits of Human Nature, ed. Warren S. Brown, Nancey Murphy, and H. Newton Malony (Minneapolis: Fortress Press, 1998), p. 2.
7 Nancey Murphy, â€œNonreductive Physicalism: Philosophical Issues,â€ What Happened to the Soul: Scientific and Theological Portraits of Human Nature, ed. Warren S. Brown, Nancey Murphy, and H. Newton Malony (Minneapolis: Fortress Press, 1998), p. 148, note 41.
18 Even Murphy is not fully satisfied with her arguments: â€œPhilosophers will not be satisfied with the arguments herein against neurobiological reductionism. Neither are we [Nancey Murphy and Warren Brown]; we hope soon to publish an adequate treatment of the issue.â€ Ibid., p. x.
19 William Hasker, â€œAn Emergent Dualist Response,â€ In Search of the Soul: Four Views of the Mind-Body Problem, ed. Joel B. Green & Stuart L. Palmer(Illinois: InterVarsity Press, 2005), p. 146. I should note that Hasker is commenting on a different, but related, passage.
27 Nancey Murphy, â€œA Nonreductive Physicalist Response,â€ In Search of the Soul: Four Views of the Mind-Body Problem, ed. Joel B. Green & Stuart L. Palmer(Illinois: InterVarsity Press, 2005), p. 105.
30 If the effect were greater than the cause then the part that is greater would come from nothing. But this is problematic for two reasons. First, if the part that is greater comes from nothing then the part that is greater has no cause. This would undermine both science and philosophy since both are based on cause and effect relationships. Second, it is a first principle of metaphysics that from nothing, nothing comes. If we were to deny this it would be equivalent to holding that things just happen â€œmagicallyâ€ without a cause.
44 I would like to thank Nancey Murphy for kindly answering some questions that I posed to her via email. I also received helpful comments from Glenn Statile, Tyler Matthew Aguilar Kimball, and Michael Stein. My gratitude also extends to Rachel Hollander for some stylistic suggestions and to Gregory R. Hansell for allowing me to make some minor revisions to this paper. In memoriam: Rev. Robert I. Gannon. Et Deo Gratias.