The Modal Argument for Substance Dualism: A Spirited Defense, Part 2

Objections and Replies

If the premises of Moreland’s argument go through, then the conclusion is guaranteed to be true; this is to say no more than that his argument is deductively valid. Further, this establishes more than the thesis that physicalism is false; rather, it establishes that SD is true. There are three major lines of objection to this argument.

The first objection is what I am calling the “overdetermination objection.” This can best be explained by a contrast with a particular issue in the philosophy of science called underdetermination. This problem is that the data available to the scientist does not alone decide which theory or scientific hypothesis is to be preferred; the data can be said to underdetermine the truth of the hypothesis.[1] By contrast, overdetermination occurs when two or more entities or hypotheses are postulated and only one is necessary for the explanation of the data.

If there is the mind, then why does it affect the body? If there is the body, why does the mind exist? It seems that if the body is sufficient for the production of physical states (and it seems that it is), then there is no need for the mind. If the body does not produce mental states, then why would the body exist? Admittedly, this latter objection may not be uttered by anyone except for the idealist variety of monists; nonetheless, it highlights the issue of overdetermination. This can also be referred to as the issue of Ockham’s razor. This principle of simplicity states that, all else being equal, the simplest explanation is the one to be preferred. Since the body can sufficiently answer the questions presented, then, the mental is simply not needed.

The answer lies in the fact that the body is not sufficient for the mind. It is not the case that the physical brain states are sufficient to produce distinct mental states. Douglas Groothuis explores this answer when he writes, “There is a difference in kind between mental and physical states that has ontological implications,”[2] and this difference lies in the fact that the mental and physical have different kinds of properties. He writes, “Whatever differs in kind cannot be identical.”[3] Here is his example: physical stuff is not the same as mental stuff. A rock is not (morally) good or (morally) bad; a stick is not loving, and so on. But if this is the case, then the difference between the physical and mental is not one of degree (where it would be the case between two physical things and two mental things), but rather of kinds. And this difference in ontological properties is sufficient to render the two non-identical.

In a similar vein, Moreland and Craig ask the reader to consider the thought of a pink elephant. Even though, upon thinking of the pink elephant, there is such an entity in your mind, there is no location in the brain or body that is that representation or is that pink elephant entity.[4] Were brain states identical with mental states, there would be this representation. However, one cannot find it.

This is not precisely sufficient to solve the problem. This is because, while the preceding does show brain states and mental states to have different properties and hence to be non-identical, it does not show that brain states are not sufficient to give rise to mental states. Perhaps there is still only one substance, and yet both physical and mental states are present within the physical body as a singular substance. This seems to miss the point of the dialectic, however. In the problem of overdetermination (or the problem of simplicity), the claim is that the physical is sufficient to account for the mental. But it cannot account for particular aspects of the mental, such as mental concrete entities (such as thoughts) having no corresponding physical properties.[5] If this is true, then the conditions of the mental do not supervene on the conditions of the physical; indeed, they cannot, because of the types of things (or substances) that they are. If this is the case, then the only legitimate shot at avoiding a reductive physicalism is to embrace substance dualism, and thus overdetermination is actually not present.

The second major type of objection is the most famous: the interaction problem. Moreland and Craig explain this problem well when they summarize: “Physicalists claim that . . . mind and body are so different that it seems impossible to explain how and where the two different entities interact.”[6] How can an immaterial soul possibly have any impact on the material universe, especially a particular body? It would make sense were there to be some measurable transfer of energy from a soul to a body, but, given that the soul is an immaterial entity, there can be no such transfer. How, then, can we even reliably understand the interaction between body and soul?

It is noteworthy that Christians—even physicalist ones concerning anthropology—typically do not press this objection. This is because such an objection, if successful, would apply to God as well. Thus, any Christian who believes God can so interact with the world (immaterial with material) should not find his faith tremendously shaken with respect to SD. Second, Groothuis argues that a lack of knowledge on how something works is not positive evidence that it does not work at all.[7] He points out, “If a good case is made against materialism and for the objective existence of mind as an immaterial substance, then there is good evidence for dualism . . . . There are a number of puzzles and conundrums concerning the activity of subatomic particles, but their existence is nonetheless well established.”[8] The interaction problem, of course, does not go away on this response—nor should it. Instead, it places the problem in its proper perspective: it is not, by itself, a defeater for SD. In fact, it would need some kind of accompanying principle that claimed, “If SD were true, then we would know how the mental interacts with the physical.” However, it is unclear how this principle would be justified; as Groothuis effectively demonstrates, we do not hold scientific theories to such standards, so why do so here? As Moreland and Craig claim, “We often know that one thing causes another without having any idea of how causation takes place, even when the two items are different.”[9]

Next, the interaction problem may not even really be a true issue in the first place. It may be that even raising the question of how the mental and physical interact is very much like asking the libertarian (in issues of human freedom) “What made Jones choose as he did?” In the libertarian question, the question simply presumes the falsehood of libertarianism, since nothing, strictly speaking, made Jones do as he did. What Moreland and Craig are claiming is that it is possible that the interaction between the mental and the physical is not an indirect process or one that uses an intermediary (if it were, the request for an interaction source or method becomes quite clear). Instead, it may be that such interaction takes place directly, with no intermediary.[10] If this is right, the interaction question is a non-starter.

It still seems to me as though the substance dualist owes a positive account of what is going on with interaction, even if one takes the view that such interaction is direct and immediate. While I do not know precisely how they interact, I suppose the interaction takes place on the level of intentions for actions. This would be a form of agent-causation where one is able to agent-cause her intentions, and, so long as nothing interferes or the agent does not countermand her earlier intentions with new ones, she acts on those intentions. In these cases, what happens is the agent’s choice is a direct one, and it would start brain processes that lead to a decision for action (rather than merely intention). When the mind acts on the body, then, it does so in a causal process that leads to action unless a new intentional chain is started.

Actions that happen to the body, on the other hand, become less clear. It seems that the body is the physical vehicle the mind uses to interact with the physical world. If it is damaged such that it cannot be used, it impairs the mind’s ability to act within the physical world. This partially explains why injured persons seem not to be able to think (thinking does involve physical processes in the human body, even if the physical cannot fully account for thinking); they are tied interactively to the body. Admittedly, this is highly speculative, but it seems to fit the facts.

Notice the first two major lines of objection do not specifically rebut any given premise in (1-7) above. Rather, they take the form of broad challenges to SD generally, so that an opponent may say something like, “I do not know what is wrong with Moreland’s modal argument above, but given these challenges to SD, there must be something.” This third line of objection is much more specific. It challenges (2), which was: “I can strongly conceive of myself as existing disembodied.” The challenge is not that (2) is false, but rather that (2) is unjustified.

Stewart Goetz makes the distinction between weak and strong conceivability, and suggests that what is at play in Moreland’s argument is of the weak variety. The major concern, for Goetz, is that support for (2) will be hopelessly circular. In order to strongly conceive that I am not identical to my body, for example, I must be aware of the contingency of the embodiment relationship (Goetz’ term for the connection between soul and body). Of course, in order for me to be so aware, I must know that I am a substance distinct from my body. But this is precisely what we want to prove![11]

How may a proponent of Moreland’s argument respond? Moreland himself responds that we just seem to be aware of certain truths regarding ourselves and what we can and cannot do, and this awareness can serve to support (2).[12] Similarly, Moreland and Craig argue that we have a basic modal intuition, and we are acquainted with it directly. If we have direct knowledge that we are “enduring . . . [selves] who” exist “as the same possessor[s] of all . . . [our] experiences through time,” then this shows us “a person is not identical to his or her body . . . but rather is the thing that has them.”[13] Of course, if one knows this way that one can exist disembodied, then the contingency of the embodiment relationship and SD follows; this is just an entailment of the direct awareness, upon reflection. But this reflection is not question-begging nor circular. With these objections discussed, one must now turn to applications to the local church.

Application

There are at least two applications that can be made to the thesis that Moreland’s modal argument for SD can be justifiably held in the face of contemporary objections. First, we can have a real existence in the intermediate state. Paul wrote in 2 Corinthians 5:8, “We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord” (KJV). Without getting into a full textual analysis and comparative Bible study, I assume there is an intermediate state. If there is, then it seems Paul is asserting that we exist in that intermediate state, even if we have no body. This is not available to most other views.[14] While it is true that even on SD, the resurrection body, which is greater than disembodied existence for humans, awaits, we nonetheless can exist as ourselves in the intermediate state; we will not fail to exist during that time.

Second, we have a strong motivation to take care of our earthly bodies, since God gives us at least two major reasons to do so. First, this is because we are judged according to the works we have done in the body on this earth. According to 2 Cor. 5:10, each one of us will be “recompensed for his deeds in the body, according to what he has done, whether good or bad” (NASB). Second, and closely related, the body we have been given requires our stewardship. Just as God could have given us a different earth (or perhaps even a different kind of earth), nonetheless, this is the one we have, and we must take care of it as good and wise stewards. Similarly, this is the body we have been given by God, and we must take care of it. Proponents of SD should never minimize either the future or current importance of the body, whether imperfect (as now) or perfect (as in the resurrection).

Conclusion

This paper purported to show that Moreland’s modal argument for SD can be justifiably held in the face of contemporary objections. First, I expounded on premises (1-7), exploring both the deductive validity and reasons for affirming the premises. Second, I examined three major lines of objection and provided responses to them. These responses, I took it, were sufficient to undercut their force against SD. Finally, I provided two basic applications for believers in SD within the local church. Moreland’s modal argument, while not decisive for everyone, should at least be sufficient for the traditional believer in SD to be justified in holding it.

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[1] Samir Okasha, Philosophy of Science: A Very Short Introduction (New York: Oxford University Press, 2002), 71.

[2] Douglas Groothuis, Christian Apologetics (Downers Growe, IL: InterVarsity Press, 2011), 394.

[3] Ibid., 395.

[4] Moreland and Craig, Philosophical Foundations, 234.

[5] Groothuis, 395.

[6] Moreland and Craig, Philosophical Foundations, 243.

[7] Groothuis, 403.

[8] Ibid.

[9] Moreland and Craig, Philosophical Foundations, 243. David Hume and his views on causation notwithstanding.

[10] Ibid., 243-44.

[11] Goetz, 45. This works against (2) since in order to know that you can exist disembodied, you must know that you are a substance distinct from your body. But that is just to assume SD, and hence the same circularity arises.

[12] Moreland, The Soul, 127.

[13] Moreland and Craig, Philosophical Foundations, 238.

[14] This is available to a hylomorphic view that does not take a numerically identical body to be necessary (e.g., one must simply have a body that is hers, not the numerically same body as on earth).