Our current understanding of how the physical brain creates our mind should in my opinion be sufficient to reject the idea that our personality can exist in a non-physical form.
It is true, and will probably always be true, that science does not understand everything about how our brain/mind works. It is, for example, a total mystery how the basic functionality of the brain hardware creates a conscious mind. In fact, it is pretty much a mystery what a conscious mind is.
Thus, in the same way that theists can push an increasingly elusive God into the gaps that still exist in our understanding of the physical universe, supernaturalists can try to make a soul or spirit fit into the gaps in our current knowledge about the brain. I argued in my previous article about this subject that since an appeal to the supernatural is unnecessary for understanding the mind, it does not really explain anything, and since we reject these kind of pseudo-explanations in other situations in life, we should also reject it here.
The belief in a soul (or spirit) is closely tied to belief in human immortality. We have always observed that the human body is destroyed by natural processes after death. For our conscious self to survive physical death, we would need to have some component that is not material, and that survives death, bringing our personality, thoughts and memories into some trancendental existence. The ancient Egyptians used embalment to try to preserve the body for the afterlife. Most contemporary religions who espouse an afterlife doctrine argues that since we have a soul (or spirit), we don't need our bodies. We can still somehow live on.
As much as I personally would like to believe in an afterlife, I find that it contradicts everything we currently know about the world. Thus, I cannot believe it.
Now, I must hasten to add that there are many different definitions of both "soul" and "spirit", and this can easily confuse any debate to the point of becoming meaningless. Both 'soul' and 'spirit' is often used as a reference to artistic expression, a person's deepest conviction, or the depth of a person's character, and many other meanings. I am not presently discussing such things. I do refer to 'soul' (which I for this purpose consider synonymous with spirit) only in the meaning 'a non-physical entity that can carry our conscious selves after the body is destroyed.' If we have such a soul, this means that 'we' can survive death, and we will preserve at least some of our memories and personal qualities from this life. This being will have a sense of being a continuation of a past corporal life, of being 'us' in a real sense.
There are two dillemmas, or problems, I would like to point out to those who believe in such a soul.
Firstly, some supernaturalists point to known holes in our scientific knowledge of the world. Or they point to ill-understood, or perhaps more correctly, counter-intuitive scientific theories like quantum mechanics. I see this as an appeal to inaccurate knowledge. How can we reasonably conclude that lack of knowledge about certain details necessarily, or even probably, point us in the direction of the ancient beliefs of cultures that often didn't even know that the Earth was round? If a new discovery should actually point us in another direction, surprisingly giving us some support for the idea that we do have a soul, fine, then we should go along with that. But future developments are just as likely to point in the opposite direction (or more so). To hold on to a belief that conflicts with all present knowledge, expecting that evidence will mysteriously appear to support it in the future, is obviously irrational.
Furthermore, I will point out that the progress of scientific discovery has been consistently leading us away from supernaturalism and towards wholly naturalistic explanations. As science has been able to shed more and more light on the workings of the universe, previous supernatural explanations have been found superfluous at best, flawed at worst, and were rejected. The understanding of electricity has explained to us how lightning works. If there still existed people who believed in ancient Greek mythology, they would perhaps still postulate that somehow lightning bolts were really, somehow, on a metaphysical plane, the works of an angry Zevs, but I doubt anybody else would consider this a serious explanation.
The argument above is inductive, and somebody could still argue that sometime, in the future, scientists will discover facts that finally supports their particular supernatural beliefs, but in doing so, they violate everything we call common sense. Natural laws are derived from continued observation and inductive arguments, and once you have seen apples falling down a sufficient number of times, you no longer really believe it is possible they will fall upwards tomorrow.
The reason I suspect that quantum mechanics is currently en vogue as a hiding spot for the soul is that this is a fantastically counter-intuitive branch of science, and it is also complicated, generally only understood (if 'understood' is a good term here) by people who have a firm grasp of mathematics and physics. Previously, the theory of relativity has been popular among adherents of all sort of pseudo-science and new age'isms. It has the same convenient qualities as quantum mechanics: it is difficult to understand and its implications are quite baffling. Where understanding is lacking, it is easy to try to fit in some preconceived ideas. I am certainly no expert in either field, but I have never seen anyone giving a rational explanation of why QM or relativity should really support any form of supernaturalism. Rather, I see many examples of complicated terms being misused, and often used to baffle believers to conclude that a particular preacher knows more than he or she really does. Thus, I admise caution in adapting the terminology from science and using it where it does not belong.
The second problem I want to point out to supernaturalists who believe in the soul is an argument I already touched in my first article.
We know from empirical data that physical damage to the brain sometimes permanently damages a part of a person's memory. Sometimes, also, various abilites and talents are lost. When the physical brain is damaged, through accidents, disease or use of restricted substances, the personality and memory is directly affected. Sometimes scientists can learn a lot by observing which parts of the brain is damaged, and what effects this have on the patient, thus making meaningful conclusions about how the brain operates.
Now, if we really have a soul, which somehow retains all (or most of) this information independent from the physical brain, why does physical damage to the brain have this effect? Furthermore, as a person dies, more and more of the brain is destroyed, and the personality disappears along with it. This is a tragic spectacle to experience for anyone who has seen a loved one die a slow death. We see no evidence that there is a soul who keeps the mind alive through the decay and eventual destruction of the brain.
Why, then, should we believe that when the brain is totally destroyed, the personality, memories and abilities suddenly reappears in a non-physical form? Is the soul a metaphysical backup of our physical brain that is somehow liberated, tranformed to spirit form (whatever that is) and can live on?
I will reassert that the belief in a soul is a rudiment of an ancient, supernatural understanding of the world. It may have make sense for an ancient. who tried to understand how a person can live, to postulate an inanimate power within that was the 'real' person. It could then follow that this power, or soul, could survive death. But when it became obvious that thougths are directly linked to electrical and chemical processes in our physical brain, this view ceased to be rational. It defies reason and it defies the actual facts we have on the table. That many intelligent, otherwise rational people subscribe to this idea, I attribute to our species' remarkable tendency to be conservative in retaining beliefs and practices long after their usefulness is over.
The 'soul' is a relic of the past, an expression of nostalgia. To a significant degree it is also an expression of our desire for immortality. But wanting something to be true does not make it factual.
