Ibn Sina’s Flying Man

Image by Richard Mohler

The following is a draft of a paper I wrote for Prof. Laywine at McGill University for Early Medieval Philosophy.

The soul, or the self, plays a crucial role in many of the world’s religions and cultures. In the monotheistic religions, the soul is our connection with God. It is that which our free will resides in, that which is morally responsible, and that which participates in everlasting life. In Hinduism, the individual soul is merely a piece of the world’s soul – an energy which flows throughout all things living. In Ancient Greek, the soul is that which continued on to live in Hades after the death of the body. In various cultures, the idea of ‘spirit’ or ‘ghost’ illustrates the existence of something immaterial that contains all a person is – their personality, desires, thoughts, and wants. In all of these cases, there is a distinct separation between the soul and the body. In most of them, the soul is that part of us which is immaterial and the body is that part of us that can act within the physical world. Scientific discoveries in the last 200 years, particularly concerning neurobiology and psychology, have granted credibility to a contrasting view of the relationship between mind and body. The discoveries of biological mechanisms for memory, emotion, personality, decision making – characteristics that traditionally distinguished one person from another – provided foundation for a view that the mind was in fact material. In this view, the mind is the consequence of billions of electrical synapses across an extremely complex network of neurons. Almost 8 centuries before these discoveries, Ibn Sīnā (Persian polymath, philosopher, and physician) proposed a thought experiment to indicate the immateriality of the soul: “the flying man”. This paper will analyze the main points of the flying man thought experiment, discuss the scientific discoveries made since its articulation, and see if and how these scientific discoveries affect the strength of Ibn Sīnā’s flying man.

Ibn Sina was born around 980 C.E. in Afshana, Greater Khorasan into an academic family (cite). By that time, Herophilus discovered that nerves were responsible for sensory input as well as motor output; Erasistratus found that the brain was divided into the cerebrum and the cerebellum; Galen describes the connection between paralysis and the severing of the spinal cord; Ahmed ibn Sahl al-Balkhi insisted that psychotherapy could aid in mental illness and clinical depression and that these illnesses could have either physiological and psychological causes; and Ibn al-Haytham began experimenting between sensory input and sensory perception, writing about the body’s relationship with the nafs, or soul. When Ibn Sina was a teenager, he studied Aristotle’s metaphysics through the commentaries of al-Farabi, and at 16, turned to the study of medicine. In his volumes The Canon of Medicine, Ibn Sina described neuropsychiatric conditions, including hallucination, insomnia, mania, nightmare, melancholia, dementia, epilepsy, paralysis, and stroke. It is apparent that Ibn Sina was not only extremely versed in the science that was available in his place and time, but was also a leader in scientific development, especially that which related to the human body. It is upon this knowledge that he proposes the flying man thought experiment to us.

The flying man argument proceeds as follows: Imagine a man is instantly created, fully mature in body and mind, his limbs are separated in a way that he could not see them or feel them. Further, he would not have the faculties of sight, hearing, touch, or smell and would be floating in a void, not lifted by some bed of air which he could feel. In essence, this man would have no knowledge of his own organs or appendages, the external world, or where he physically begins or ends. Despite this situation, Ibn Sina posits that the man would still “know that he exists as uniquely a single thing” (207). As such, it doesn’t follow that that which we call ‘I’ is the whole body – if it were, the flying man would not be able to conceive of himself as existing without the knowledge of his organs. That thing which perceives itself as existing, is, Ibn Sina argues, the soul. Appropriately, the soul is separate from the body, and thus not corporeal.

There are two points that are of my interest in Ibn Sina’s thought experiment. Firstly, it is the fact that the flying man must be an adult – fully developed in his mental state. This, we can assume, is placed in contrast of a child or a baby whom we may not be able to conceive of being able to think “I exist” whilst floating in the air. Does our inability to conceive the baby to think such a thing reflect the baby’s lack of a soul or the expression of the soul acknowledging itself? If it is the former, what is it in the baby’s development into adulthood that necessitates the existence of the soul? If it is the latter, perhaps it is something like the learning of language or the physical experience of interacting with an external world that acts independently of him that grants him the ability to express ‘I exist’. It is unclear whether or not the man has memories of that which he’s restricted from (sights, sounds, the knowledge of his organs) or what the adult possesses that differentiates him from his baby analogue. Perhaps this is just a parameter added to make it easier for us to imagine the scenario.

Secondly, it is interesting that Ibn Sina does not remove the man’s organs all together. In a related passage, Ibn Sina comments on the necessity of the organs: “I believe that [my organs] are instruments of mine that I use to fulfill certain needs. Were it not for those needs, I would have no use for them. I would also be myself even if they did not exist.” That is to say that the only reason we have sight is because we need to see, lungs because we have to breath, and legs because we have to stand. If we did not have these needs, we could discard the organs without discarding our ‘self’ – this indicates the separation of the ‘self’ from the bodily organs. The floating man could have been the disappearing man, a thought experiment in which, by some divine intervention, the needs – and matching organs – of this man disappeared one by one. His need for oxygen was abolished and so were his lungs; his need to smell was abolished and so was his nose; his sight and eyes; and so forth. As his organs disappeared one by one, we could ask the same question we’ve asked the flying man, “does the disappearing man have a concept of ‘I exist?’”. Though the disappearing man seems like it fits with Ibn Sina’s observation of the necessity of the organs driven by their need and not by their inherent membership in the ‘self’, he does not frame his thought experiment as such. Instead, he makes it clear that the organs of this man do exist – that his body, as well as the external world, exists – but rather the fact that he does not know it exists. Again, like the separation between the child and the adult, Ibn Sina’s choice of using the flying man rather than the disappearing man may be a decision to allow his audience to better conceive of the thought experiment as realistic. Perhaps Ibn Sina expects us to conclude that if the knowledge of the soul exists without the knowledge of the body, the soul exists without the body.

These questions may make the flying man argument seem weak, but it is important to understand that the flying man argument was never meant to be analyzed as a proof. As most thought experiments are, Ibn Sina intended the flying man argument to be an indicator to a truth that could not necessarily be proved without falling into circular logic. In Book I, Chapter V of the al-Shifa, Ibn Sina explains the indication of conceptual matters: “If one desires to indicate [conceptual matters], such indications would not, in reality, constitute making  an unknown thing known but would merely consist in drawing attention to them or brining them to mind through the use of a name or a sign which, in itself, may be less known than [the principles] but which, for some cause or circumstance, happen to be more obvious in its significance…none of the [more complex of conceptual matters] can be shown by proof totally devoid of circularity” (23). As such, the flying man’s philosophical weak points are merely spaces for interpretation and attacking them in a way which calls for complete coherence is unfair. However, the flying man is integrated within a more explicit argument found in 205-208 and with it, we can, to the best of our abilities, draft the explicit points the thought experiment is making.

There are two major points that the flying man is directing us towards. After seeing the scientific discoveries since the 8th century, we will come back to these points to evaluate their validity. Firstly, Ibn Sina’s flying man indicates that sensory input is not necessary for the understanding of ‘I am’. The man does not need to interact with the external world through his senses in order to conceive that ‘he is’. Further, he does not have to sense the existence of his physical body – he doesn’t have to see his skin, hear his voice, or smell his odor – in order to come to the same conclusion. Essentially, physical interaction with the world through the body is not a necessary part of the soul. Secondly, the soul knows itself to exist without knowing the body to exist. This point is, in fact, explicitly made: “He would not know that any of his organs exist, but he would know that he exists as uniquely a single thing”. Whether or not the man knows the concept of the human body, or have memories of once having one, is unclear. This is significant because there is a difference between not having the knowledge that one has a body and can interact with an external world which also exists, and not being certain that one’s body exists whilst knowing that an external world exists and one could interact with it if a body existed. It is the same difference between not knowing the existence of eyes or eyesight and not knowing whether your eyes have been surgically removed. If Ibn Sina means the latter, then the knowledge of the existence of organs may still be necessary for the soul – the knowledge of the body may still be an integral portion of the soul. However, if he means the former, then it can be said that the flying man indicates that knowledge of the body as a concept is not required for knowledge of the soul. Because which Ibn Sina means is ambiguous, I will assume the former as it is more explicit in its separation of mind and body.

There are a few implications of the dualistic view that Ibn Sina’s flying man suggests that is beyond the scope of this essay. However, I feel that it is important to keep them in mind, as they indicate the overarching consequences of a soul separate from the body. First, the immaterial soul allows for life to continue in soul form after the death of the body. Further, because ‘I’ exists fully within that soul – our body being only a tool the soul uses to act within the physical world – we lose no part of us in the death of our bodies. This consequence is coherent with the Islamic perspective of eternal life with God in paradise. Secondly, the soul allows our actions to be caused by something beyond the material realm. Without this allowance, our actions would be attributed to physical events which would have been triggered by the physical events prior to them and so on. One commonly accepted result of us being purely physical beings is a deterministic world view – and consequently the lack of free will. Free will is a cornerstone in the Muslim faith. The word ‘Islam’ translates to “peace/surrender”, that is “peace will come to those who surrender to Allah” – surrendering necessarily referring to an act of will. Considering the parallels between Ibn Sina’s philosophy and his faith is important in gaining the proper prospective…

We have briefly analyzed the contents of Ibn Sina’s flying man thought experiment and identified the two major points that the experiment is trying to indicate. Further, we have considered the major ambiguities in the experiment and their significances. Lastly, we briefly looked at the overarching consequences of the separation of body and mind and the parallels between Ibn Sina’s argument and his faith. What is now required of us, is to observe the scientific and technological advances over the last 1000 years and see if and how it affects Ibn Sina’s experiment. We will look at these advances in three distinct relationships: the relationship between the body and the mind; the relationship between the brain and the body; and the relationship between the brain and the mind.

The relationship between the mind and the body as indicated by Ibn Sina is analgous to the relationship between master and tool. The mind uses the body as a tool to actualize its will in the physical world, but the body itself is not necessary for the mind to exist. Ibn Sina compares our body to be as separate from us as our clothes are; but because of us being accustomed to having a body, the relationship between mind and body is more concrete than the relationship between mind and clothing (CITE). With the introduction of new technologies that have become vital to keeping us both physically alive and socially productive, Ibn Sina’s distinction is strengthened. For example, the cell phone and internet have become an crucial extension to our ability to communicate. They are like a set a vocal chords that can reach across around the world to exactly the receiver we want. For those who have lost the ability to speak, such as Stephen Hawkins, voice box technology, text-to-speech, and advanced word processing software have enabled their ability to audibly communicate. Functionally, the voice box and the human voice is identical except for its effectiveness. The same can be said about hearing aids replacing the ear, laser eye surgery or eye transplant surgery for the eye. Further, in the case of internal non-sensory organs, the development of artificial hearts, mechanical arms and legs, and dialysis machines that replace kidney function, we are not intuitively hesitant to replace our biological body parts with mechanical body parts that perform the same function. It is clear that when we do become, for all intents and purposes, cyborgs, we do not change in personality or life choices. We retain the same ‘self’ and the same continuity. A particular example that’s particularly striking comes from an experiment done recently (2008) in Pittsburgh. Probes, the size of human hairs, were inserted into a group of chimpanzee’s primary motor cortext, the region of the brain that controls movement. The probes took signals from the brain and sent them via a computer program to a mechanical arm physically strapped onto the chimps. With only their brains, the chimpanzees were able to continuously change the speed and direction of the arm and the gripper and 61% of the monkeys were able to, with some training, use the prosthetic limbs to feed themselves marshmallows while their own arms were tied behind their backs. “The monkeys had come to regard the robotic arm as a part of their own bodies” (CITE). In this situation, it was not that a non-functioning body part was replaced with a machine that performed a similar function. Rather, a brand new appendage was added. The chimps ability to adapt to using the mechanical arm, directly attach to their brain, further represents the little inherent commitment that exists between that which we consider ‘us’ and our physical. Although it is humorous to conjure up a science fiction character, such as Dr. Octopus from the Spiderman series – who has 8 mechanical tentacles that are directly fused into his spinal cord – there is a famous science fiction thought experiment that is pertinent to our discussion: It is safe to say that every functional component of the body is replicable on a physical level. As such, there is nothing in the nature of technology that prevents us from making a mechanical version of very part of the human body – it is just a limitation of our current developments in technology. Let us assume that we have now reached a point in technological development where the entire human body has a mechanical analog. Replace your heart with a mechanical one – are you still ‘you’? Of course you are – this is no different than the mechanical hearts we have presently. Now replace your arms with mechanical arms, and legs with mechanical legs (or wheels if you’re feeling daring). The kidneys, liver, stomach, intestines and skin also get replaced with mechanical analogues. The process continues with the rest of your body parts, one at a time. The thought experiment asks, “at which organ swap do you cease to know that ‘you’ exist?” If you are fully mechanical, every biological body part replaced with a motor or a microchip, and are still able to conceptualize “I am”, then what is attaching the immaterial soul to that particular physical collection? This thought experiment is meant as a indicator to the same truth as Ibn Sina’s flying man. Namely, the relation that our bodies have with ‘us’ is particular functional and not essential. The one exception in the current field of organ replacement technology is the brain. Brain transplants do not currently exist and no research suggests that it will be possible in the near future. What is evident is that the brain is necessary for most of the functions of all the other organs (breathing / digestion) and definitely responsible for all of the conscious motor functions. It seems relevant then, to consider the relationship the brain has with the body and whether or not the brain is closer to the ‘self’ than the other parts of our body.

To understand the relationship between the brain and body as it applies to mind body duality, we must first understand the fundamentals of how the brain works. The brain is the core of the central nervous system in all vertebrae and most invertebrate animals. Composed of a careful collection of tens of billions of neural cells, the brain works to receive signals from sensory input and sends output to the rest of the body in the form of muscle commands or hormone release. Without the brain, the organs alone can perform their automated functions (such as the filtering of liquid waste in the kidneys) but are disabled in the moderation of those functions. In essence, the brain is the physical origin of what we perceive to be non-automated movement – movement by volition. Sensory input from all of the sense organs and status information from internal organs (such as communication from sexual organs) is received by the brain and results in either automatic reflexive movement or conscious knowledge. The brain has evolved to work in complex harmony with the physical body and its separation from it is less clear than with the mind and body. For example, in amputees, the phenomenon ‘phantom limb’ is the sensation that an amputated or missing part of the body (eg. limbs or appendix) is still attached and moving accordingly to the rest of the body. The neurological cause for this was discovered in the early 1990s by Tim Pons at the National Institute of Health. He found that the brain, when missing inputs from a certain organ, rearranged itself to receive signals from surrounding neurons. As the neurons responsible for receiving input from the hand were near those that were responsible for receiving input from the face, Pons showed that stroking the face gave the subject the impression that their missing hand was being stroked. It is clear that the brain is physically not committed to the necessity of the entire body as a whole – it adapts to the removal of certain body parts. For example, the brains of paraplegics are able to adopt to a new center of gravity and the brains of deaf or blind people display a heightening in the sensitivity of the other senses.

It is also important to distinguish between the passive brain and the active brain. The passive brain, the autonomic nervous system, was hinted in Galen by was not fully explained until the 1700s by Francois Pourfou du Petit of Paris, performs functions that are below the level of consciousness.. It is responsible for the automation and moderation of our internal functions such as heart rate, digestion, respiration, salivation, perspiration, and sexual arousal. In contrast, the active brain, the somatic nervous system, is responsible for voluntary control of skeletal muscles and the reception and perception of sensory inputs. The reason this separation is important is because Ibn Sina’s thought experiment pertains to our personal, internal, perception of our conscious relationship with our body. It appeals to our understanding of using our body parts as tools to actualize change in the physical world. The autonomic nervous system is not a part of this relationship. It works independently of ‘our’ knowledge and volition and even if it was the case we willed it to stop or change, it would continue as it was built to. The passive brain, just as with the other organs, can be categorized under Ibn Sina’s branch of ‘existing due to another necessity’; without the need to breath, eat, sense, or feel, we would not need the passive brain. Thus, the passive brain is only a tool as limbs and clothing are tools and is not a part of that which we conceive as the ‘self’. What is left then, is to consider the relationship between the active brain and the mind.

EEG (electroencephalography) activity was first described in 1875. Richard Carlton a physician in Liverpool, discovered that the exposed cerebral hemispheres of rabbits and monkeys produced measurable electrical signals. Human study of EEG began in 1920 by German psychologist Hans Berger and focused on the detectable electrical fluxes during an epileptic seizure. In 1953 Aserinsky and Kleitman described the EEG recordings of REM sleep (sleep that produces dreams). Most recently, various specific patterns of electrical brain activity were mapped to categories of thought – for example, a certain pattern for the creation of a memory versus the recollection of a memory. The significance of EEG to our discussion is that these electrical signals are physical representations of what Ibn Sina describes as our ‘intellect’, that which enables us to think ‘I am’ in the first place. On the other hand, it strengthens the monist idea that the ‘soul’ is purely material. That is, that the brain is the source of the intellect and thus the soul; if the flying man did not have a brain, he would not be able to conceive of ‘I exist’.

The brain takes sensory input and creates models that our conscious mind works to comprehend. A particular example of this model creation is exposed in optical illusions. Because the sensory input from optical illusions do not conform to the brain’s existing models, the brain replaces the image with a model that makes the most sense. Upon the learning of language, these models are paired to words and through language, the mind is able to combine models to create complex thoughts and ideas. Our interaction with these models composes the majority of our conscious experience. The relationship between these brain models and our experience of consciousness is emphasized in studies regarding dreams. When we sleep, we are deprived of conscious sensory input. As such, our brain creates models for itself and dreaming is the experience of these models. What is interesting is that interacting with these models in dreams results in similar physical and emotional reactions as if the models were real. During nightmares, our pulse increases, we sweat and hyperventilate, and no matter how ridiculous the dream is, we often are trapped with the conception that it is reality – until we wake. Ibn Sina appeals to dreams as evidence of imaginative thinking external to the material world in ________.

A particularly relevant example of the brain creating models in the absence of sense perception is the sensory deprivation psychological experiments pioneered by John C. Lilly in 1954. The experiment is as closest real experiment analog to the flying man thought experiment. In sensory deprivation tanks, the subject is blindfolded and floats in a soundproof chamber on top of salt water. His fingers, toes, and limbs are spread out and a swimming cap is worn to prevent the movement of hair. The subject floats in this tank for up to 48 hours. Within 3 hours of sensory deprivation, subjects claimed to begin hallucinating shapes and figures. By 5 hours, the hallucinations became more vivid, producing something closer to a lucid dream. Smells and sounds were also a part of the hallucinations. None of the subjects claimed to lose their sense of ‘self’, but almost all showed signs of their brain’s attempt to create models from memories and from scratch. Without sensory input, and in a non-dreaming, conscious, state, the brain still has the ability to provide a conscious experience.

Developments in the brains role in personality, emotions, and mental disposition are also relevant in our discussion. Though Ibn Sina does not suppose the evidence for an immaterial soul to require anything beyond its ability to say ‘I exist’, the identity of that soul that exists, ‘who am I?’, is a relevant extension. Customarily, our conception of how one person is different from another, disregarding physical, body, and – in part – cultural differences, is built upon that person’s personality, the combination of the sensitivity of their emotional triggers and their decision making processes. Furthermore, when asked to identify our own identities, we appeal to memories: our past, our home, our culture, our experiences and how those memories have shaped our sensitivities towards certain stimulus or how they have molded our decision making processes. Since the introduction of clinical psychiatry in the early 19th century and the compiling of the DSM (diagnostic and statistical manual of mental disorders) in the 1980s, almost every major aspect of personality can be modified through physical modification of the brain. Anti-depressants disable the personality traits of motivation, excitability, or depression. Lobotomies removed all variations in mood, motivation, and desire. Drugs used to treat attention deficit disorder such as Methylphenidate or Adderall increases the ability to concentrate. Further, disorders in the brain directly cause disorder in personality. Manic depression and bipolar results in huge swings in mood. Strokes remove the ability to attach language to ideas. Brain degenerative diseases such as Alzheimer’s and senile dementia destroy the ability to logically reason, lowers intelligence, and disables the ability to create short term memories. Of course, Ibn Sina’s flying man is not attempting to extrapolate personality and identity as a portion of the soul, but if it were true that all of that which consisted our identity was housed physically in the brain, what is the significance of our immaterial soul? What would we consist of as souls that lived on eternally after our bodies rot away? Without identity, the concept of everlasting immaterial soul-life seems to, at least to me, lose a lot of its appeal; if the concept of ‘self’ was void of identity, what is the significance of saying ‘I exist?’ The relationship between the soul and personal identity is beyond the scope of this paper, but, given modern psychiatry’s definition of these physical causes to mental character, it is a conversation worth having elsewhere.

We now return the two major points raised by Ibn Sina’s thought experiment. The first being that sensory input is not necessary for the knowledge that “I exist” and the second being that knowledge of the body is not necessary for knowledge of the soul. Through our discussion of our mentality about prosthetic and mechanic organs, technology as an extension of our bodies, and the psychological effects of sensory deprivation chambers, it seems to remain true that sensory input is separate from our brain’s ability to create conceptual models and that our relationship towards our bodies is simply one of master and tool. Through our discussion of the brain’s ability to create models of streaming consciousness through dreams and the cyborg thought experiment, it also seems to remain true that the knowledge of our bodies have little to do with our ability to conceive of our existence. However, in our analysis of neuroscience and psychological advances since Ibn Sina, it becomes clear that the brain – particularly the somatic nervous system – has a nature different from the rest of the body. It is irreplaceable by any mechanical analog, adapts to the loss of function of any other organ, produces measurable physical effect when we think, creates conscious experiences when we dream  or are sensory deprived, creates models which we then use to rationalize, and its debilitation results in drastic changes in our identity. The brain as such cannot be labeled as the rest of the body is in relation to our soul. In fact, there is nothing in the flying man to suggest that the brain is not our soul. Ibn Sina responds to this by saying that the brain cannot be all that the self is. “[Even if it is true that the brain] is identical to [the soul], then my perception that ‘I am’ must be my perception of that thing. But one thing from a single perspective cannot be both what is perceived and other than what is perceived” (208). That is, what would be doing the perceiving? Later, he quickly disregards the necessity of his response by stating that since it is only though experimental knowledge that he knows that he has a brain, his brain is secondary to his soul – that the soul knows itself, without experimental knowledge, after which it can know the brain (208). However, given our brief investigation in the role the brain plays in our mind, it seems fully possible to know that “I exist”, through the activity of the brain, without knowing that it is the brain that has granted me that ability. Of course, this is the first step of a materialist view of personhood, which is not what I would like to contrast with Ibn Sina at this point. What is significant here is that one of the flying man’s main premises, that all of the body is disposable when what necessitates it is removed, does not apply to the brain. Our discussion points to the fact that what necessitates the brain may be the ability to declare, “I exist”.  Ibn Sina, in a footnote, addresses this problem briefly, “if it is the [case that an organ is necessary for the self to exist], then the organ would be just part, albeit an essential one, of what is identified as the self” (208). I speculate the inclusion of that statement was only meant to serve as a failsafe in the case that an organ was found to be necessary to the knowing of the self, as it has become evident to us. As such, Ibn Sina does not focus on it and does not account for it in his writings about our soul in the eternal life.

After a millennium of science, the majority of Ibn Sina’s flying man holds its ground. However, the recent developments in neuroscience and psychology suggest that the brain plays an essential role in the ability, or at least expression, of one to think that “I exist”.