「靈魂」是人類其中一個最久遠的概念。
它似乎解釋了許多東西：人的同一性(personal identity)，以及智慧和意識之來源。
而物質如何產生意識，更是迄今科學未能解決，連頭緒也沒有的難題。
然而，儘管幾百年來的努力，現代科學並沒有找到靈魂存在的確鑿證據。
如果說靈魂是「超自然」的，是否就解決了這問題？
以下是我在讀哲學碩士「科學與理性思考」課程時，期末論文的一部份的答案。
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Question:
3. What are the major arguments for and against mind-body dualism? What impacts does the development of neuroscience have on the traditional view of mind? Do you think that it is reasonable to believe in the existence of an immaterial soul? Why or why not?
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Q3: (Immaterial
soul and mind)
In this essay, I will focus on the discussion of interactionist substance dualism, which
posits the existence of a physical world and immaterial soul (“soul” hereafter), and the two can interact. It is because (1) this form
of mind-body dualism is the most
popular, and (2) other forms of dualism (e. g. property dualism and epiphenomenalism)
do not contradict with physicalism as much as the dualism I will write about.
Since most people believe in the existence of a physical world, I shall also use the arguments for and against the existence of soul, as those for and against dualism, respectively.
1. Arguments for immaterial soul
1.1 Mental-physical distinction
Philosopher
Frank Jackson proposed a thought experiment: how “red” feels like is irreducible
to knowledge about the physical world. [1] To many, the “soul hypothesis” has a
crucial function to explain mental phenomena. Humans and some animals are very
different from other entities: we have the abilities to perceive, remember, be
self-conscious, think and have intention.
Plants
and dead matters do not seem to share those. They are governed only by the
blind physical laws of the universe which we can study openly. On the contrary, it seems that we each have the “privileged
access” of our own mental content.
There seems to have an insurmountable gap between the mental and the physical, therefore it seems reasonable to theorize something other than the physical entities, which we call the “soul”, which is the bearer of the mental qualities.
1.2 Personal Identity
There
are also philosophical problems of what a person is, and how we can recognize
if two persons are the same (e. g. a boy and an old man, at different times).
Many theories are proposed, e. g. the body and psychological continuity
criteria; but they are all unsatisfactory. Some suggested to give up the idea
of person altogether. [2][3]
But the idea of personal identity is so natural and important to us: personal relationships, responsibility and ownership all depend on it. This problem has motivated some of us to believe in the existence of soul. Because a soul is immaterial, it cannot be divided; if every soul is unique and permanent, then we can distinguish two persons by their souls.
2. Arguments against immaterial soul
2.1 Problems of Interaction
The soul hypothesis has caused many conceptual problems. Soul is non-physical and thus very different from physical objects. If so, how can souls cause the changes in the physical human body? On the other hand, how do the stimuli caused by the external world on the physical body can possibly affect and be perceived by the immaterial soul?
Some people claim that they have seen ghost figures, or say that ghosts can scare or harm people. However, if these “ghosts” are non-physical souls, then how can they be seen? Being immaterial, they cannot interact with light to see people either. Philosopher Daniel Dennett said the idea of ghost is self-contradictory: sometimes they can pass through walls, but at other time they can move objects. [5]
2.2 Incompatibility with science
The
problem of interaction was just one of the many conflicts between the idea of soul
and modern science.
Physics: In science, all events are physical, and any event is caused by a previous event in accordance to physical laws. Soul by definition is not physical, and therefore if it interacts with the physical world (e. g. a person raising her hand), there would be events not caused by other physical events. This violates the causal closure principle of physics.
Even
if the soul can somehow cause physical events, there is still a scientific
problem. Physicist Sean Carroll wrote that if there is any “spirit particles/ forces”, we would have
already detected it. [6] If there is an event without a physical cause, it may
also break the law of conservation of
energy.
Neuroscience: Much has been known about
how the brain works since the idea of soul. It is well-known that many physical
alterations to brain can change the mental qualities we attribute to soul. These
includes brain damage, tumor, psychiatric disorder, memory loss, electrical and
magnetic stimulations, pharmacological and optogenetic manipulations, resulting
in memory loss, change in perceptions, beliefs and personality. Neuroscientist
David Eagleman described a patient with pedophilic tendency increases over
stages of brain cancer. [7] Libet’s experiment and other similar experiments
suggest that “our decisions” form in the brain before we “decide” them. [4]
If
we can correlate all mental activities with regions of the brain, how can we
still say that we must need a soul to account for the mental phenomena?
Since science has been so successful in explaining the natural world, it follows that if we have no strong reason to believe in soul, when science and the soul hypothesis are in conflict, we should abandon the latter.
3. Possible responses
3.1 Soul as an Explainer
In
response to the problems of interaction, philosopher Richard Swinburne said our
inability to understand how soul interacts with physical body does not mean
they do not interact. [8] The mental-physical distinction is still very clear
that we need soul to explain the mental phenomena as well as personal identity.
This
line of thinking is analogous to the use of the idea of immaterial “vital
force” to explain how dead matter can constitute living things. Nowadays, scientists
generally agree that organisms emerge out of the complex arrangements of
molecules and the chemical reactions among them. “Vital force” plays no part in
this scheme, because it is not needed: we have known enough about organisms.
Biologist Julian Huxley jokingly compared vital force to “locomotive force”
which makes the vehicles move. [9] Similarly, the soul hypothesis may one day
play no part in our explanation of mental phenomena.
Furthermore, the soul does not seem to explain personal identity satisfactorily. For if souls are immaterial, that they do not occupy spatial location, how can we distinguish one soul from another? There is also the problem of counting the number of souls: e. g. consider two persons, each with half of a brain; if the half-brains are put into the same body, is there one soul or two souls? [3] It seems that the concept of personal identity is one which is helpful to us in daily social situations instead of imaginary cases. It is erroneous to infer an immaterial entity from a confusing concept.
3.2 Incompatibility with Science
Soul theorists, if not dismissing a large part of science, may respond to the disagreements between their hypothesis and science in the following ways.
First, altering brain structures and activities may seem to change the mental activities. However, we may compare the relationship between a brain and a soul, with that between a violin and its player. If the violin is broken, the bad play may not be due to the skill of the violinist; similarly, the alteration of the brain does not imply that of the soul. [10]
Second, some may distinguish mind from soul, with the mind being physical and responsible for the mental phenomena. Soul does not directly interferes with the physical world through the mind, thus is not in conflict with any physical laws or the results of neuroscience.
These auxiliary theories may indeed avoid the conflicts between science and the soul hypothesis, however with bad consequences. For they take away the explanatory power of the soul, which was once the main reason of the soul hypothesis. Soul has become something without any function or effect. If everything can be explained through the physical events, by Occam’s Razor we have no need of the presupposition of a soul.
In conclusion, because of the (1) incompatibility between the soul hypothesis and science, (2) problems of interaction between soul and physical objects, and (3) failure of the soul hypothesis in explaining personal identity, there is no rational reason to belief in immaterial soul and therefore mind-body dualism.
Reference:
[1] Jackson, F. (1982). Epiphenomenal qualia. Philosophical Quarterly, 32(127), 127–136.
[2] Parfit, D. (1971). Personal identity. The Philosophical Review, 80(1), 3-27.
[3] Parfit, Derek. “Divided Minds and the Nature of Persons” in Edwards, Paul (Ed.). Immortality. Prometheus. 1997, pp. 308-315.
[4] Libet, B., Gleason, C. A., Wright, E. W., & Pearl, D. K. (1993). Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). In Neurophysiology of Consciousness (pp. 249-268). Birkhäuser, Boston, MA.
[5] Dennett, Daniel. Conciousness Explained. Back Bay Books. 1992.
[6] Carroll, S. M. (2011, May 23). Physics and the Immortality of the Soul. Retrieved from https://blogs.scientificamerican.com/guest-blog/physics-and-the-immortality-of-the-soul/
[7] Choi, C. (n.d.). Brain tumour causes uncontrollable paedophilia. Retrieved from https://www.newscientist.com/article/dn2943-brain-tumour-causes-uncontrollable-paedophilia/
[8] Swinburne, Richard. The Evolution of the Soul. Oxford University Press. 1997.
[9] Gillies, Mary Ann. (1996). Henri Bergson and British Modernism (revision of author’s PhD thesis), (pg. 31). McGill-Queen’s Press.
[10] Calef, S. (n.d.). Dualism and Mind | Internet Encyclopedia of Philosophy. Retrieved from https://www.iep.utm.edu/dualism/
