(I continue the case for the soul and some objections to the view)
The last philosophical argument for substance dualism concerns the nature of free will. Advocates of libertarian free will (as the model of human action) affirm that intentional action is the exercising of a first or originating mover to bring about some effect for a reason. This view entails that a person is a substance that has the active power to bring about an event and exerts this power as the first-mover (originator). A person also has the ability to refrain from exercising this active power (could choose not to take a certain action). Last, a person could act for a certain reason or teleological goal.[i] An example is Darren (as an unmoved mover) who chooses to turn on the television in order to watch a sitcom. Darren is a substance (person) who had the ability not to exercise the action of turning on the television, but chose to nonetheless for the purposes of a teleological goal of entertainment (sitcom). This libertarian act is spontaneous in that there were no causal predecessors that were sufficient to explain it.
On the other hand, determinism is the view that for every event, there are prior conditions such that nothing else could have happened. This reduces human action to mere happenings as every action is causally determined by events prior to the action (even before the birth of the agent). Human actions are just parts of causal chains of events. A third view is compatibilism which claims that libertarian freedom and determinism are compatible, so that determinism does not eliminate free will. Compatibilists accept event causation (explained above), but reject determinism by embracing a belief/desire psychology such that these states of belief or desires cause the action to take place. This view denies that the substantial agent himself directly produces the effect.[ii] In any case, both determinism and compatibilism deny agent-causal relations, i.e. they deny that in any causal chain the first member can be a person or agent.
Although I cannot make an extensive argument for the libertarian view of human agency, most scholars admit that it is the most commonsense position and such is adopted by most. Without this view, it would be difficult to make sense of moral obligation and responsibility, which presupposes that we have freedom of choice.[iii] Introspection provides one of the best avenues of knowledge of the truth of libertarian agency. As Moreland and Rae explain in regard to processes of deliberation, “we are aware of the fact that we are enduring agents who continue to possess and exercise the active power of control throughout these processes, all the while reserving the power to refrain from so acting as we teleologically guide our deliberative processes or sub-acts toward our intended goal.”[iv]
If physicalism is true, then it follows that determinism is true. Since physicalists depict a person as a physical system of parts, human action is understood as law-governed happenings that are deterministic or probabilistic as part of causal theory of action. This leaves no room for a libertarian view of human action as Thomas Nagel explains, “Everything I do or that someone else does is part of a larger course of events that no one ‘does,’ but that happens.”[v] Since there is no room for agent causation (from a physicalist perspective), there is nothing in me that has the capacity to choose something. Material systems (such as our bodies) change over time due to the initial conditions and the laws of chemistry and physics, but there is no room for free will on this view.[vi]
If the libertarian view of free will is true, then this counts as evidence against physicalism and is the reason a majority of naturalists reject it. On the other hand, substance dualism provides the best metaphysical account for libertarian freedom as it depicts an agent (immaterial soul or substance) who has causal power to make or refrain from actions without being affected by a physical causal chain. Moreland and Rae outline three features of a libertarian agent which are very comfortable within a substance view of the agent.[vii] First, there must be a “distinction between the capacity to act or refrain from acting and the agent that possesses those capacities.”[viii] Second, there must be a unity between the various capacities in the agent. Third, since free will acts take time to complete (and can include sub-acts), there must be an enduring agent that gives unity to these acts, i.e. it must be the same self at the beginning of the action who guides the teleological aspect to the end. We have already seen that the physicalist notion of the person as a property-thing cannot provide these features, whereas a substance view can. It follows that an immaterial spiritual substance is the best explanation of a libertarian agent. This spiritual substance is not just immaterial, but more than this; like God, angels, or disembodied souls, this substance would possess the “ultimate capacities of thought, feeling, consciousness and active volitional power.”[ix] Substance dualism is the only view that has the ontological entities to account for such an agent.
With the strong philosophical evidence for substance dualism, it is important to analyze the arguments that physicalists (and naturalists) use against the view. First, physicalists claim that the interaction between an immaterial soul and a physical body seems impossible because the substances are so different. How can a pin prick cause a “feeling of pain” in the soul? Or vice-versa, how can the soul cause something to move, such as raising your arm? This objection makes the assumption that just because we do not know how the interaction takes place, then we can assume the interaction does not take place. We are, however, aware of many entities that are very different, but have causal relationships – such as a magnetic field that can move a tack or gravity that can attract a planet millions of miles away.[x] Even though we have no idea how these example interactions take place, scientists are convinced nonetheless that they do. Furthermore, if God exists, it is conceivable that He can have causal interaction with the universe itself, although He is spirit and affects a material universe. Last, this objection is impossible to answer because the interaction between the two substances is direct and immediate – there is no intervening mechanism and thus this objection should not even arise.[xi]
Related to this is the objection that because of Ockham’s razor (between two equally valid alternatives it is better to take the simpler) one should chose one substance (physical) instead of two substances to explain the same phenomena. This principle is true, but in looking at the evidence given above, physicalism is inadequate (especially personal identity through change) and thus by adding a second substance the phenomena is better explained.
A third objection is called the problem of other minds. This challenge states that if dualism is true, we can never know other people have mental states because they are private and inaccessible in a third party manner. This leaves us skeptical if other minds exist in the first place and if they do, whether they have the same mental states that we do. Maybe the physical sensation that I experience as red is experienced by someone else as the color blue.[xii] This apparent problem is highly exaggerated. Evidence for substance dualism cannot be used as evidence against it, i.e. because our mental states cannot be reduced to physical states which are accessible to third party observation is evidence for substance dualism, not against it. Second, we can know (by argument of analogy) that when we observe someone pricked with a pin, see them grimace and say, “ouch!” that they are most likely experiencing a mental state of pain. This is an inference to the best explanation of the facts. Moreland explains that “the mere logical possibility that we are wrong about the mental states of another is not sufficient to justify skepticism.”[xiii]
[i] Ibid., 123-4.
[ii] Ibid., 123-9.
[iii] J.P. Moreland, What is the Soul? Recovering Human Personhood in a Scientific Age, 34-5.
[iv] J.P. Moreland and Scott B. Rae, Body & Soul, 133.
[v] Thomas Nagel, The View From Nowhere (New York: Oxford University Press, 1986), 114.
[vi] J.P. Moreland, What is the Soul? Recovering Human Personhood in a Scientific Age, 34.
[vii] J.P. Moreland and Scott B. Rae, Body & Soul, 150-1.
[viii] Ibid., 150.
[ix] Ibid., 154.
[x] J.P. Moreland, What is the Soul? Recovering Human Personhood in a Scientific Age, 47.
[xi] Ibid., 48.
[xii] Ibid., 48-9.
[xiii] Ibid., 49.