The failure of arguments for the existence of the soul

One might wonder why philosophers bothered presenting arguments for the existence of the soul. After all, introspection seems to confirm that the soul exists. But, alas, introspection does not reveal the existence of the soul. Introspection may (arguably) reveal the existence of one's mind, but introspection does not reveal that mental activity occurs in a substance that is separable from the body or that mental events can occur without one's brain after death. Such claims need a philosophic defense – which they received most famously from Plato and René Descartes.

Plato's arguments are rooted in his ancient metaphysic theory. Plato believed in ‘the Realm of Forms’ – a collection of perfect abstract objects, in which physical objects ‘participate’ to be the objects that they are. (Chairs participate in the Form of Chair.) According to Plato's ‘theory of recollection’, when one learns something new, one is not acquiring new knowledge but recalling something that one knew before birth while living among the Forms. Since one must have existed before one's body in order for this to be true, Plato concluded there must be a soul.Footnote ² But, since no one takes the theory of recollection seriously anymore (we know that learning is not merely recollection), and since that theory assumes an even more outdated theory (Plato's Theory of Forms), Plato provides us with no good reason to conclude that souls exist.

René Descartes is an advocate of substance dualism and thus also of the soul hypothesis.

Descartes presented three arguments that the mind and body must be different and separable entities, and thus that the mind is in fact a soul: the argument from doubt, from conceivability, and from divisibility. Descartes famously began his Meditations by doubting the existence of the physical world (including his body) but concluded that his mind could not be doubted. If the mind can't be doubted but the body can, Descartes thought, then they must be different and separable things. Further, Descartes argued, since he can conceive of his mind existing without his body, and thus it is logically possible that his mind exists without his body, they must be separate things. Lastly, since the brain can be divided into separate parts but the mind cannot be divided, Descartes concluded, they must be separate things.Footnote ³ And if they are separate things, the mind must be a soul.

All three arguments fail. The argument from doubt fails because ‘doubtability’ is not the kind of property that can distinguish objects. Does, for example, Lois Lane doubt that Superman is a genuine hero? Of course not. Does she doubt that Clark Kent is a hero? Of course she does. Yet Superman and Clark Kent are one in the same person, the latter being the alias of the former. I suppose that Lois could, like Descartes, wonder if Superman is even real – perhaps it is all a dream. But that would not alter the point; the doubtablity of one object cannot be used to distinguish it from another. Besides, the mind can be doubted; eliminativism – the philosophical view that doubts the existence of the mind – has become a legitimate, and growing, philosophical theory.

The argument from conceivability fails because the fact that something is conceivable does not mean it is logically possible. One might conceive that the morning star exists while the evening star does not, but since the morning star is the evening star (they are both the planet Venus), one existing without the other is not logically possible. Further, conceiving that one's mind exists without one's body may only be possible because one has a limited understanding of what one's mind is. One cannot conclude that minds are necessarily un-embodied unless one is perfectly aware of all aspects of minds. Indeed, our growing knowledge of the brain's relation to the mind suggests that minds are embodied. (We will talk more about this later.)

Lastly, the argument from divisibility fails. In the same way that ‘doubtability’ can't delineate substances, neither can ‘divisibility’. But, more importantly, the fact that minds are in fact divisible has been revealed by the phenomenon of split brains. When one's corpus callosum, which connects the brain's two hemispheres, is severed (in surgery) or damaged (by a stroke), one's mind, literally, becomes divided. Each half of the body is controlled by a separate mind – a separate stream of consciousness. In controlled experiments, Nobel Prize winner Robert Sperry communicated with each half of such minds separately, conveying to and eliciting different information from each.Footnote ⁴

The fact that the arguments for the existence of souls fail is enough reason to doubt their existence. When it comes to claims of existence, the burden of proof is on the believer. As Bertrand Russell famously pointed out, if I want to believe that a teapot orbits the sun, I cannot rationally do so unless I provide evidence for that belief. (Sure, no one can prove a ‘celestial teapot’ doesn't exist – I can always claim it is too small to be seen – but that is no reason to believe it exists. That would be a fallacious appeal to ignorance.) Likewise, even if the existence of the soul can't be disproved, belief in the existence of the soul is irrational unless positive evidence or argument can be given in favor of its existence. Thus the failure of the most well regarded arguments for the existence of the soul is a detrimental blow to the soul hypothesis.

Many would argue, however, that the existence of the soul can be disproved – or, at least, buried beneath an insurmountable amount of counter argument and evidence. Before we look at the scientific objections, let us first consider the philosophical objections that have been leveled against the soul.

Philosophical arguments against the existence of the soul

Let's begin by pondering a question. If decisions happen in ‘your soul’, then when you decide to move your arm, why does your arm move and not, say, my arm? Your decision happens in your soul, of course, but in virtue of what is your soul connected to your body and not mine? It can't be because your soul is closer to your body than mine. Souls are not made of matter and only matter can have location in time and space. So in virtue of what does your soul belong to you and not me? No satisfactory answer to these questions has ever been given.

Even if we ascribe a physical location inside your body to your soul, one still wonders, what facilitates the causal connection? After all, I can be inside my car, but unless I have the key, know how to drive, and the car is gassed up, it's not going anywhere. So, how does the soul drive the body? How could a non-material entity interact with a material one? No satisfactory answer to these questions has been given either.

An even more troubling fact is this: the soul can't control the body. The Law of Conservation of Energy (which states that energy cannot be created nor destroyed) and the Law of Conservation of Momentum (which states the total momentum of any system always remains constant) are well established. Also well established is the causal closure of the physical, which says that physical events can only have physical causes. Many scientists and philosophers maintain that this latter law is known a priori (without the need of sense experience), but it is also confirmed by the fact that any time we have gone looking for the cause of physical events, it has turned out to be another physical event.Footnote ⁵ This includes events in the body, like bodily movements, which causally trace back to events in the brain. If the soul reaches out from beyond the physical realm, to cause things to happen in the brain and body, it would violate all three of these principles. It would be adding energy to the system of the body (or brain), and ultimately the universe; it would not be allowing the amount of momentum in the system that is the physical body (or the brain specifically) to remain constant, and it would be a non-physical cause of a physical event.

Of course, any or all of these principles could be shown false in the future, but the fact that something is possibly false is no reason to think it is false. The evidence is in favor of these principles; unless they are overturned they constitute a problem for soul belief – a problem philosophers call ‘the problem of downwards causation’.

As you can see – because of the failure of the philosophical arguments for the soul and because of the problem of downwards causation – the philosophical prospects for the soul hypothesis are not good.

The brain does everything the soul is supposed to do

Phineas Gage was a young railway foreman in the 1800s. An accident, on September 13, 1848, caused a tamping iron to pass through his skull – entering under his left cheek and exiting through the top of his skull – pulverizing part of his forebrain.

Gage survived, but his personality completely changed. Whereas he had been a gentle, respectable man and a responsible foreman, he became a rude and aggressive man and an irresponsible worker. He was no longer able to be employed as a foreman; he was annoyingly indecisive and careless, abandoning plans almost before he made them. His subsequent rudeness and profanity didn't help his employment prospects either. Perhaps worse, women were advised not to be in a room alone with him, as he would attempt to molest them.Footnote ⁶

Gage's case challenged the classic soul hypothesis because physical damage cannot change one's personality if personality is housed in a non-physical thing like the soul – yet it undeniably had done this in Gage. Thus, it was concluded, personality must not be housed in the soul; instead it must be a result of the functioning of one's brain. The case of Phineas Gage, we might say, gave the soul one less thing to do – one less thing for it to explain. It pulled personality from the realm of the non-physical soul, and placed it squarely within the realm of the physical – the neurophysical.

Recently some have challenged the severity of Gage's personality change, but the point is moot. Gage set us down the path of discovery. Neuroscientists subsequently have discovered the brain areas responsible for language use and understanding (Broca and Wernicke's areas), for physical sensations of touch (the Penfield Map), for emotions (The Limbic System), for reasoning and decision making (the frontal lobes), for visual sensations (the aptly named visual cortex)… the list goes on. Many of these discoveries, in fact, were fueled by cases similar to Gage's, where specific mental capacities were lost when people suffered specific kinds of brain damage. Now we even know why Gage's personality changed.Footnote ⁷

Although not everything about how the brain works is fully understood, it is now undeniable that all mental activity is a direct result of brain activity. Not only has personality been pulled from the realm of the non-physical soul into the realm of the physical brain, but everything that was once the purview of the soul – emotions, language, decisions, sensation, memories, personality – is now known to be the purview of the brain.

The inadequacy of the soul hypothesis

The soul hypothesis was supposed to function as an explanation for our behavior by being the cause of our intentional actions and dispositions. But it has always been lacking in this regard. Good explanations don't raise more questions than answers, but what the soul is made ofFootnote ⁸ and how it causes changes in the body, has always been a mystery. Now, since neuroscience has shown us that the cause of all we do is neural firings in the brain, not the activity of the soul, there is no explanatory gap for the soul to fill. Neuroscience has rendered impotent any explanatory power the soul hypothesis might have had. And hypotheses that explain nothing are not good explanatory hypotheses.

Attempts to save the soul from such objections do not succeed. For example, one might suggest that the known correlation of mental events to neural firings merely shows us how the soul operates. Although neuronal firings explain our behavior, the activity of the soul could be interjected to explain neuronal firings. (‘Controlling neurons is how the soul controls the body.’) But such attempts harm the cause more than help. Not only would such a suggestion violate the physical laws mentioned at the end of the last section, and not only do we know that all brain activity is ultimately caused by physical reactions in the nervous system, but such an attempt renders the soul hypothesis wholly irrational. To explain why, let me draw an analogy.

Many scientists used to think heat was the product of a material called phlogiston that flowed into objects to make them hot and flowed out to make them cold. When we discovered that heat is actually a result of the movement of particles, phlogiston defenders suggested that ‘making particles move is how phlogiston makes objects hotter’. But, of course, that was only an ad hoc excuse to save their theory. There was no need to hypothesize the existence of phlogiston – it didn't explain anything. Heat could be accounted for solely by the movement of particles; no extra substance was needed. Defending the phlogiston hypothesis in this way was merely a result of wishful thinking on the part of those who were emotionally attached it as a pet theory. And so the phlogiston hypothesis fell out of favor.

Hopefully the analogy is clear. In the same way that heat can be accounted for solely in terms of the movement of particles, so can behavior be accounted for solely in terms of the activity of the brain. And hypothesizing another substance – whether it be phlogiston, or the soul – to account for activity that is already explained is only a less-simple irrational ad hoc excuse made to save the theory grounded in wishful thinking.

The soul defender might also insist that, despite the evidence, brain damage does not affect mental capacities. When it seems that someone has lost mental capacities upon the loss of particular brain functions, perhaps those capacities are actually still intact – safe and sound, in the soul. It's just that the brain damage prevents the soul from being able to communicate this fact to the outside world.

Again, such rationalizations hurt more than they help. First, such attempts are ad hoc suppositions interjected merely to save the theory from falsification. Worse however, such suppositions are untenable. Am I supposed to believe that Phineas Gage's personality remained gentle, but his brain damage was such that when he tried to act in gentle ways, he instead cursed profusely and tried to molest women? Am I supposed to believe that an Alzheimer's patient doesn't really forget their past experiences or their loved ones? Is it rational to believe that their memories are all still there, fully accessible, but when they try to describe their memories their brain damage is such that it just causes them to act or say that they have forgotten, or that they don't know who is standing in front of them? Of course not. And the silliness of such suggestions clearly reveals that they are merely desperate rationalizations to save the soul hypothesis.

All in all, neuroscience has shown that there is nothing left for the soul to do and thus no reason to suppose that it exists. Everything that was once supposed to be housed in or explained by the soul is now known to be housed in or explained by the brain.