Within the philosophy of mind, there are several nuanced views that can be held concerning anthropology and the constitution of man. Even within views that allow for immaterial human souls, there are widely varying positions held. Particularly contentious has been the view of substance dualism (SD), also referred to as Cartesian dualism. If SD is true, then, obviously, physicalist theories of mind are false; with it, likely, goes naturalism. Thus, SD can be a valuable tool in the arsenal of the Christian philosopher. Second, traditional Christian doctrine has been such that an immaterial soul is required for the intermediate state: SD can account for this, and in a way that seems intuitive and natural for the believer. Finally, we can have comfort in the death of loved ones knowing they are with the Lord. But are there any good arguments for SD? J.P. Moreland has proposed a particular version of a modal argument for SD for consideration. It is my contention that Moreland’s modal argument for SD can be justifiably held in the face of contemporary objections. First, I state the argument formally and explain the support behind each of the premises. Then, I consider three major objections to the argument and provide responses that, while not conclusive, provide reasons to think SD might survive. Finally, I give applications that may be applied for believers and the local church.
The Argument Stated
In Moreland’s book The Soul, he offers several arguments for SD. The modal argument is a particularly interesting example in that it seems to establish strongly the conclusion of SD. This is notable since, typically, arguments that purport to establish SD in reality do little more than show that physicalism is false. While doing so is surely valuable, and leaves the door open for SD, it is also consistent with types of holistic dualism (and Moreland generally wants to do more than this). This modal argument is as follows:
1. The law of identity is true: If x is identical to y, then whatever is true of x is true of y and vice versa.
2. I can strongly conceive of myself as existing disembodied.
3. If I can strongly conceive of some state of affairs S that S possibly obtains, then I have good grounds for believing that S is possible.
4. Therefore, I have good grounds for believing of myself that it is possible for me to exist and be disembodied.
5. If some entity x is such that it is possible for x to exist without y, then (i) x is not identical to y, and (ii) y is not essential to x.
6. My body (or brain) is not such that it is possible to exist disembodied, i.e., my body (or brain) is essentially physical.
7. Therefore, I have good grounds for believing of myself that I am not identical to my body (or brain) and that my physical body is not essential to me.
The initial premise, (1), is relatively uncontroversial—if interpreted in a very specific way. (1) is often referred to as Leibniz’ Law, named for Gottfried Leibniz. Much of the recent discussion has centered around the fact that (1) seems to preclude any idea of contingent identity. Contingent identity is the idea that there may be two objects, x and y, that are identical objects despite the fact they have one or more differing contingent properties. For an example, consider Socrates. In this actual world (call it W), Socrates is, say, five-foot-four in height. However, consider a nearby world, W’, where Socrates is five-foot-five. We say that the Socrates in W is the same as (or identical to) the Socrates in W’. Yet, strictly speaking, on (1) above, this is false. This is because Socrates-in-W has a property that Socrates-in-W’ does not, namely being five-foot-four, and hence they are not identical.
There are two proposed solutions to this problem—one of which will require a slight adjustment to the wording of the premise, and the other an understanding of an underlying metaphysical concept. The first solution is to adjust the Law by accounting for worlds and times. This approach is taken by Thomas McCall. He lists his principle as follows: “For any objects x and y, if x and y are identical, then for any property P, any world W, and any time t, x has P in W at t if and only if y has P in W at t.”
This solution is helpful for our Socrates problem, since the property of being five-foot-four at t in W would be had by both Socrates’, and the same thing goes for the property of being five-foot-five at t in W’. Another way to view the issue would be counterfactually: If it were the case that W were the actual world, then it would be the case that Socrates is five-foot-four.
The second solution, I think, spells out the underlying metaphysical reasoning behind the first solution. It relies on Alvin Plantinga’s theory of creaturely essences. For every concrete particular agent, such as human persons, there is an abstraction called a “creaturely essence” that contains all and only the essential properties of that essence. The creaturely essence is a set of essential properties that, for Plantinga, is itself a singular property (for Socrates, he calls it Socraeity). This property has what he calls “world-indexed properties,” where such a property P is world-indexed just in case “an object x has the property having P in W in a world W* if and only if x exists in W* and W includes x’s having P.” Essentially, world-indexed properties for creaturely essences accomplish the same thing as McCall’s solution, even while preserving the initial formulation of (1). This is because the properties discussed have their contingencies in the worlds in which they appear and all belong to the same creaturely essence. Either way, a relevant version of the law of identity stands, and this is crucial to Moreland’s argument.
Even more than (1), (2) will be the primary point of controversy in this modal argument for SD. For a reminder, (2) is: “I can strongly conceive of myself as existing disembodied.” This “strong” conception is needed, and not what Stewart Goetz would call “weak” conception. To weakly conceive of something is, as Goetz states, a “failure to be aware.” Thus, if (2) were to be weak conceivability, it would express no more than that one does not see any reason to think he is identical to his body, or that there is nothing in his awareness such that disembodiment is impossible. Such weak conceivability will not yield the conclusion Moreland draws; hence, he employs a strong conceivability. This strong conceivability is a positive; it is the ability to be aware that one can exist disembodied.
What reasons does Moreland provide for thinking (2) really is true? First, he draws relevant analogies. We strongly conceive of ourselves in particular ways that present themselves to our reasoning all the time. For example, we know that we are not the type of thing that can be subject to gradation (we are a unified individual, and not something that can become two-thirds of a person). Similarly, I can persist through change and time, and I am not merely the collection of disparate temporal or property-divided parts. If this is so, then while we do not have a knock-down argument supporting (2), we do have reason to think that we could justifiably hold (2), or that we really can conceive of how we are with respect to identity or constitution, through relevant modal intuitions.
Second, Moreland argues directly from these modal intuitions. He and William Lane Craig write, “We are aware of our own self as being distinct from our bodies and from any particular mental experience we have. We simply have a basic, direct awareness of the fact that we are not identical to our bodies . . . rather, we are the selves that have a body and a conscious mental life.” This direct modal acquaintance will provide the one who has such an awareness (that he can be distinct from his body) with prima facie justification for (2).
What about (3)? For a reminder, (3) is: “If I can strongly conceive of some state of affairs S that S possibly obtains, then I have good grounds for believing that S is possible.” This seems innocuous enough. This kind of move is made all the time in discussions on possible worlds or other imaginative alternate scenarios. Although he offers it in defense of (2), Moreland makes two points that apply to (3). First, he discusses near-death experiences. While often dismissed without a second thought, Moreland’s point is that if people’s experiences are even possibly true, then a disembodied existence is possible (which is enough to establish his point). Second, Moreland uses other modal conceptual scenarios to support (3), including that alien life on other planets is at least possible (because he can conceive of it).
(4) is an entailed conclusion, following from (2-3). (4) is stated as follows: “I have good grounds for believing of myself that it is possible for me to exist and be disembodied.” This seems fair enough, given Moreland’s argumentation so far.
(5) is stated as a nearly self-evident truth: “If some entity x is such that it is possible for x to exist without y, then (i) x is not identical to y, and (ii) y is not essential to x.” Conclusion (i) follows from the law of identity as stated in (1), and conclusion (ii) comes from an analysis of what it means to be essential. If y is essential to x, then in no possible state of affairs does x exist without y (since that is what it means to be essential).
(6) is just a definitional premise, and should not be questioned on physicalist grounds: “My body (or brain) is not such that it is possible to exist disembodied, i.e., my body (or brain) is essentially physical.”
Of course, because of everything that has come before, (7) is the final conclusion of the argument for SD: “I have good grounds for believing of myself that I am not identical to my body (or brain) and that my physical body is not essential to me.” Notice Moreland needs both sides of (7) in order to establish the truth of SD. The first part of the conjunction establishes the falsehood of physicalism, while the second does away with views that require the body as essential to the person. Can Moreland’s argument survive various objections that can be lodged against it? In the next section, I explain and examine three major objections to this modal argument.
 While it is true that any form of dualism that espouses more than one substance can on this basis qualify as a type of substance dualism, this paper will refer to Cartesian dualism as SD, and other forms of substance dualism (such as Thomistic hylomorphic dualism) as “holistic dualism” or some other nuanced term.
 J. P. Moreland, The Soul: How We Know It’s Real and Why It Matters (Chicago: Moody Publishers, 2014), 125-26.
 Pablo Cobreros, Paul Egre, David Ripley, et al., “Identity, Leibniz’s Law and Non-Transitive Reasoning,” Metaphysica, Vol. 14, No. 2 (October 2013:), 253-64.
 Thomas H. McCall, “‘I am my Body?,’” Philosophia Christi, Vol. 17, No. 1 (November 2015:), 208.
 Alvin Plantinga, The Nature of Necessity (New York: Clarendon Press, 1974), 71-72.
 Ibid., 63.
 Stewart Goetz, “Substance Dualism,” In Search of the Soul, Joel B. Green and Stuart L. Palmer, eds. (Downers Grove, IL: IVP Academic, 2005), 44.
 Moreland, 127.
 J.P. Moreland and William Lane Craig, Philosophical Foundations for a Christian Worldview (Downers Grove, IL: IVP Academic, 2003), 238. Of course, here it can be wondered why, then, there is any argument to be made at all. Perhaps one could respond that the modal intuition that leads to (2) entails we are souls, and the argument may be needed to expose this entailment in particular cases. As such, the argument is really meant to reveal implications of already-held beliefs or modal intuitions, and so falls in-between a knowing and showing style of argumentation.
 Moreland, The Soul, 127.
 Ibid., 125.
 It is true the monist who is an idealist could object to this, but a number of underlying assumptions made in this dialectic is that either some kind of physicalism is true, or some kind of dualism (holistic, SD, or otherwise). Thus, while interesting and worthy of attention, this paper will not deal with idealism.