Louise Malan | 19 October 2021 | 7 min read
The soul has been thought to exist since antiquity by, amongst others, the ancient Greek philosophers such as Plato and Aristotle. Many Medieval philosophers and theologians also assumed its existence. In the last few centuries, the idea has come under fire, largely by physicalists.
So why does this matter for us as Christians? Firstly, the Bible is clear about an immaterial aspect to the self (in Greek, the pneuma and psyche) , and a denial of the soul is thus a contradiction of God’s revelation to us. Secondly, if immaterial realities do not exist, matter is all that there is. This would mean that God does not exist, and neither does free will and thus moral responsibility. This would make the idea of sin and the gospel meaningless.
Physicalism is defined as the view that all entities are merely physical. For our purposes, the soul will be defined as a non-material substance which contains consciousness and animates the body. It is simple (not composed of parts); the bearer of personal identity; the seat of thought, reason and volition.
How is the soul different from the brain? It is immaterial. It is also simple. Brains are largely composed of neurons—made of parts, like a LEGO tower. Neurons can logically be removed and put into another’s brain and remain the same. There can be ownerless neurons. They are impersonal. In contrast, thoughts cannot be separated from thinkers. They are intrinsically personal. Jack and Jill can think the same proposition (e.g.: “Let us go up the hill”), but Jack’s thought is his and Jill’s thought is hers. Souls are unlike LEGOs because they are not composed of parts. One cannot go to the shops or to the library to assimilate more parts to one’s soul. The library contains information and only once the information becomes the object of consciousness does it become a thought.
There are three main objections to the existence of a soul by materialists:
- The physical world is closed to souls—souls are locked out and cannot causally interact with the material world.
- Souls violate physical laws.
- Souls are redundant—they have no explanatory power.
Firstly, physicalists claim the principle of “the causal closure of the physical” (CCP). According to this, every physical event has a sufficient physical cause. The substantiation for this is belief in the “In Principle Completeness of Physics” (IPCP), where it is postulated that a “complete and comprehensive physical theory of all physical phenomena” exists. The IPCP is the presupposition of physicalism.
However, why should one accept the IPCP? Afterall, it is speculative. It cannot be defined by current physical theories since they are not comprehensive and complete. Neither can it be defined by future physical theories since we cannot be sure that they exist. In fact, it is notable that the field of science has made it a point to exclude certain phenomena from its scope of study, so it could never detect these—let alone describe them—even if they were real. These facts cannot be studied by the scientific method and their existence points to the falsehood of the IPCP. These facts include first-person experience. Science studies from a third-person point of view, attempting to be objective. It has excluded very real subjective experiences. Frank Jackson’s thought experiment, Mary’s Room, demonstrates this. Suppose there was a brilliant scientist named Mary, who lived her whole life in a black and white room with black and white screens and black and white books—she had never seen anything else. She was an expert scientist in colour vision. She knew all these was to know about light and the way the brain interpreted the electrical signals from the rod and cone cells on the retina. One day, she got out of the room and saw a red apple. Did she learn something new? Of course! She learned what it was like to see red. The experience of redness was new information to her. It is something entirely subjective. Likewise, the sound of music or the taste of strawberries or the way your limbs feel when you move them about are all bits of information. On these types of information, science is silent; it is beyond the scope of science.
Additionally, the objection assumes that if one does not know how one entity causes another, then it is unreasonable to think that they are causally related, especially if they are different. However, this objection is flawed. For example: scientists do not know how gravity exerts its forces on planets, but it is known that it does. Here the cause is different from its effects: an invisible force versus solid bodies. There is so much evidence that the mind does cause things in the physical world, it is unreasonable to doubt it. How is it that whenever I intend to lift my arm, I do? Why does this not happen only 40% of the time, and the other 60% of the time I do the chicken dance? Moreover, a question about how A causes B is a question about an intervening mechanism between the two. But it is entirely possible (and likely) that the causal link between the soul and the body is immediate—that is, without a mediating mechanism.
Furthermore, if CCP were true, it would be the case that brain states could cause other brain states, as well as mental states, but mental states could not cause brain states or other physical realities or anything at all since these mental states do not constitute a substance. Yet we have reason to think that mental events do cause things, including physical events. The placebo effect is an example of this. The patient’s trust in a doctor or medicine in general results in measurable effects secondary to an intervention that should not have caused that particular effect. This same effect does not obtain when the intervention is administered to comatose patients, implying that consciousness causes physical effects independent of purely physical causes. Another example is neuroplasticity in stroke victims, where thinking in certain ways changes the brain. Or certain cognitive therapies for mental health, where changing one’s thinking can, at times, be equally or more effective than the prescribed drugs for changing behaviour. The way the person thinks has an impact on them physiologically.
The second objection states that every physical event is caused by another physical event governed by physical law. If some mental event intervenes in this causal chain, it would be violating the physical law. Most commonly, this is stated in terms of the Law of Conservation of Energy: the total energy in a closed system remains constant, sometimes stated as “energy cannot be created or destroyed.” It is said that causation involves a transfer of energy. If the soul caused physical events, it would be creating energy, thus violating the law.
On the contrary, physical laws do not cause anything by themselves. They are conditionals. If the right cause and the right initial conditions are present, then the effect will happen. This is consistent with different causes and different initial conditions. The reason it may seem plausible is because CCP is assumed. It is not the laws of physics, but the assumption of CCP which would lock out mental causes. It assumes that the physical world is all there is. In this case, of course nonphysical things could not cause anything. With regards to the Law of Conservation of Energy: it pertinently states that energy is constant in a closed system, which is perfectly compatible with miracles or free choices. This would simply mean that the system is not closed. And the popular “energy cannot be created or destroyed” is not equivalent to the previous statement. It is not even accepted by mainstream physics, which holds that mass and energy came into existence a finite time ago. Furthermore, the idea that causation implies the transfer of energy is unsubstantiated, in fact it may even be false. This is demonstrated by twin particles in quantum physics (quantum entanglement), which can be separately by long distances, but changes to the one particle occur simultaneously to the other despite their separation. If energy were to be involved, it would have to travel faster than the speed of light to effect this change, which is not possible. So, it is not even true in current physics that all causation is energy transfer.
Finally, the physicalist’s third objection states that advances in neuroscience show that there is nothing that the soul can do that the brain cannot—it offers no explanatory power and is redundant. This is a clear instance of applying Ockham’s razor: do not multiply causes beyond necessity. Proponents of this objection will say that postulating the existence of the soul is to add a cause that does no explaining, while the physical is a sufficient causal explanation. Those who defend the existence of the soul will point out that the phenomenon of mind must be explained and that “it is not enough that mental states and brain states are causally related or constantly conjoined with each other in an embodied person.” Physicalism requires an identity relation between the mind and the brain. But if there is something that is true about the one, that is not true about the other, then they are not identical. In this case, it would be rational to posit the soul as a cause for mental events. Now if a scientist stimulates part of the brain and it causes a mental event such as a feeling of fear or pleasure, this does not prove that the mind and the brain are identical. It merely shows that they are causally linked. There are, in fact, several things that can be said about the mind, but that are not true about the brain by itself. These include: the ability to make free choices, the ability to reason, and retaining personal identity over time. These are elaborated on in the first article, which makes positive arguments for the existence of the soul.
To summarize, those who claim that there is no such thing as a soul have three main arguments—all of which are flawed. Firstly, the soul is locked out. This is not true because the IPCP and CCP are false assumptions. There are examples of mental causation in our lives, and poor understanding about how something works does not mean that it cannot work. Secondly, the soul is said to break physical laws if it causes anything in the physical world. This is false by virtue of CCP being a false assumption and causation not necessarily being energy transfer. Thirdly, souls are said to be redundant. This can be disproved by pointing out that the brain and the mind would have to be identical for this objection to hold, but that the soul has explanatory power that the brain by itself lacks. Thus, the main arguments against the soul are unsuccessful, and in light of the strong arguments for the existence of the soul, it is reasonable to believe that such an entity exists.
The opinions and views expressed in this article are those of the author and do not necessarily reflect the views and opinions of the employees and members of Ratio Christi South Africa.
 See 1 Thessalonians 5:23.
 “2015.02.26 Angus Menuge – In defence of the soul,” available at https://www.youtube.com/watch?v=u8h7iEQg-J4, accessed October 17, 2021.
 Jaegwon Kim, Mind in a Physical World, (Cambridge: MIT Press), 1 & 40.
 Frank Jackson, “Epiphenomenal Qualia,” The Philosophical Quarterly, vol. 32(1982):(No. 127):127, available at https://www.jstor.org/stable/2960077, accessed October 17, 2021.
 Menuge, In Defence of the Soul.
 Moreland J, Craig W, Philosophical foundations for a Christian worldview, (Downers Grove: InterVarsity Press), 233.