(In this part, I continue the case for the soul using philosophical arguments)
Not only is theology a valid realm for knowledge, but philosophy can provide insight into the nature of the soul. The first philosophical argument for substance dualism I will outline pertains to whether mental states are physical, i.e. whether our conscious properties (such as thinking or being in pain) are really physical. To make this argument, it is important to understand Leibniz’s Law of the Indiscernibility of Identicals. This law states that if you have two identical things (e.g. Darren Rodrigues and the son of Ken Rodrigues), then there is only one thing you are talking about.[i] If Darren Rodrigues and the son of Ken Rodrigues are the same (and they are), then whatever truth applies to Darren Rodrigues will also apply to the son of Ken Rodrigues. If one thing could be found that is not equivalent between these two, then they couldn’t be identical. Physicalists claim that mental entities are really equivalent to physical entities (such as brain states or properties of the brain). If we can find just one thing that is not equivalent between the mind and the brain, then it would be shown that they are not identical and thus physicalism is false. Dualism, as the only other option, would be true.[ii]
As you pay attention to your own awarenesses, it becomes apparent that our mental properties are not equivalent to physical properties. Our own mental states have an inner, subjective, “first person” introspection that is not available to anyone else. These “first person” experiences are only available internally with no “third person” accessibility. Even God himself cannot have my first person experiences, although He could have an exhaustive “third person” knowledge about them. We are directly aware of our own mental states and they are necessarily individually owned, i.e. they could not belong to someone else. If these mental states are in fact physical, then they should be publicly accessible. Although there is a correlation between our mental states and activity in the brain, this does not show that a mental event is spatially located in the brain – otherwise if it was, it would be available to analyze (neurologists agree it is not). Another way that mental states are different is that our sensations may be vague or familiar or unpleasurable. Strictly speaking, these sensations cannot have these features if they are physical.[iii] It is evident that mental states have features that physical states do not and therefore cannot be reduced to physical states.
Another argument is that in acts of introspection, we are simply aware of ourselves as “enduring, immaterial centers of feelings, thoughts, beliefs, desires and willings.”[iv] In fact, our knowledge (or awareness) of this is basic and fundamental. We are aware of our own center of consciousness which is distinct from our bodies and any mental experience we have. I have direct knowledge of the fact that I am not equivalent to my body, but rather am an immaterial self that has a body and mental thoughts.[v] The reader can do an experiment by examining the series of experiences that occur when taking a walk. Imagine as I go out to my backyard, I have different experiences (in succession) of a tree planted in the middle of the lawn. Through introspection I am aware that it is I myself who has the series of tree sensations (through sight). It is “I” who is experiencing each sensation of the tree. I am also aware that the same “I” had the other tree experiences. As Moreland explains, “Through self-awareness, I am aware of the fact that I am an enduring I who was and is (and will be) present as the owner of all the experiences in the series.”[vi] Obviously, I am not identical to my experiences, but rather I am the conscious thing that has had the experiences. Also, if I were to lose an arm, I would not become a partial person, for instance, and thus what I call “I” is a mental substance. Physicalists wish to deny what has been the commonsense view of the self throughout history. This fact is directly accessible to us through introspection and is a valid form of knowledge.
A third argument for substance dualism is our identity through change. On a physicalist view, our body (although living) consists of physical parts that extend spatially with events happening to it through time. The question is whether such physical artifacts (such as our body) can maintain strict sameness through change (since the cells in our body are all replaced every seven years on average). Since the inception of philosophy, the ship of Theseus (an ancient king of Athens) has received focus for answers to this problem. As Theseus brings his ship into port, parts are replaced plank by plank. Through many trips, eventually all the parts are replaced such that there no longer remains any of the original parts. The question is whether this ship was replaced or repaired? Is the ship literally the same ship as the original ship of Theseus, or is the ship a new ship that resembles the original? If the answer is not obvious, suppose that instead of replacing each plank with another wooden plank, a frozen Jell-O plank is used. Now suppose we eventually gather up all the parts that were replaced and build another ship using those parts. Which ship is now the original ship of Theseus – the frozen Jell-O one or the one that was rebuilt? Most philosophers agree with commonsense intuition that the rebuilt ship with the original parts is Theseus’ ship.[vii]
This example demonstrates that physical artifacts cannot maintain strict identity through change, which creates a problem for the physicalist as to how a person can be the same person as two years ago, much less two minutes ago. On a dualist view, the entity that remains the same through change is the soul, which is causally related to another substance (body) able to gain or lose properties without affecting its identity. This personal identity is consistent with Leibniz’s Law of the Indiscernibility of Identicals and allows me to say that I presently (at thirty eight years old) am the same person as when I was six years old (playing in the school yard) with potentially entirely different physical parts and properties. On this view, personal identity is absolute and does not come in degrees, i.e. I am not sixty percent of the person from years ago, I am one hundred percent the same person. Personal identity is grounded in your soul such that if you have the same soul, you are the same person, if there is a different soul, you are a different person.[viii]
Physicalists are forced to define personhood in a different manner; most choose either a body view or a memory view. For both of these views, human persons are depicted as “property things” (like a chair) that undergo change such that personal identity comes in degrees, i.e. “a person is a series of person-stages related to each other in an appropriate relationship.”[ix] The difference in these two theories is how that relationship between each person-stage is explained. On the body version, the connections between the different stages are the mental states which are connected to the “same” body. Since we are always in a state of physical change, advocates of this view must explain how the body is really the “same”. Some claim this is done by having a certain percentage of parts in common with the previous stage or some may claim each stage must be spatiotemporally continuous with neighboring stages. Another option is to claim that each new body stage must resemble neighboring stages in appearance.[x] For the memory view, it is the continuity of psychological characteristics that determines personal identity. It is the brain that carries with it these continuities, such as likes and dislikes, goals and interests, character traits and feelings. Our memory is what links each person stage together to give us personal identity. If our brain ceases to be, then we lose our personal identity.
Through introspection you are directly aware that you are not equivalent to your body or to a group of experiences, but a thought experiment can demonstrate these views faulty nonetheless. Imagine that someday it becomes possible for a surgeon to split your brain and body in half and attach both halves to two other half bodies without brains. Suppose we call the first person (body and brain combination) P1 and the two new persons P2 and P3. After the surgery, P1 no longer exists, but P2 and P3 do. Because of redundancies in the brain, in this experiment, assume that both P2 and P3 have the same memories as P1. On the body view, it is difficult to determine if there would be two new people, or if somehow either P2 or P3 is the person that once was P1, or if P1 is partially survived in P2 and P3. A similar difficulty with the memory view entails. If both P2 and P3 have the same memories, you have to conclude that both P2 and P3 are the same person as P1 (which is impossible). It is more likely that memory serves as an epistemological test for identity, i.e. memories presuppose personal identity.[xi] This example demonstrates that a person is not identical to their body or memories.[xii] The physicalist view has difficulty in accounting for personal identity, whereas the dualist view is quite apt at explaining it as the unity throughout a period of time consistent with our experience of being human.
[i] J.P. Moreland, What is the Soul? Recovering Human Personhood in a Scientific Age, 14.
[ii] Ibid., 15.
[iii] Ibid., 19.
[iv] J.P. Moreland and Scott B. Rae, Body & Soul, 191.
[v] J.P. Moreland, What is the Soul? Recovering Human Personhood in a Scientific Age, 29.
[vi] Ibid., 29-30.
[vii] J.P. Moreland and Scott B. Rae, Body & Soul, 176-7.
[viii] Ibid., 178-180.
[ix] Ibid., 181.
[x] Ibid., 181-2.
[xi] Ibid., 189.
[xii] Ibid., 184-6.