To begin with Avicenna also places doubts on the existence of the world. But it is not the radical skepticism of Descartes, where reality is deceiving and the subject finds themselves unable to determine whether they are waking or dreaming. The world does exist for Avicenna, but his examinations were into why it exists, a question which would have puzzled the First Teacher (Aristotle). For Avicenna, the entire world is itself contingent and is necessary not through itself, but through another, a Necessary Existent. It is this Necessary Existent which is the ground for all reality as we see it, not the Efficient Cause of Aristotle or the Neo-Platonist Final Cause. When Avicenna begins his discussion on the Soul in his Shifa', he begins by observations of the world around him, a contingent world whose necessity, and not being qua being, was in doubt. He tells us at the beginning of his investigation that we commonly observe certain bodies which perceive, feed and reproduce, these are differentiated from other bodies in the sub-lunar sphere such as rocks, fire or chairs and tables that do exist, but are different. It is what can be referred to as living bodies, which concern Avicenna. These bodies possess what he calls "a principle for the issuance of any actions that do not follow a uniform course devoid of volition". For example fire and air would always move upwards whilst water and earth downwards. This principle, he calls the soul, and it is the necessity for why living creatures move, reproduce and feed, even if it is not the actual cause.
The purpose of his thought experiment is primarily as a memory aid to assist future students in remembering the conclusion of Avicenna's examination into whether there is a soul and what that is. He meant it as a final defence for his students to help them resist being taken in by clever arguments and sophistry, to find that elusive I which thinks, reasons and is the principle of all human enterprise, and that we also share a similarity in with all living creatures. Avicenna is telling us that the soul exists as an immaterial perfection of both our bodies and our forms, which he later on uses to prove the possibility for eternal life of the rational part of the soul, the intellect, fitting this in nicely within an Islamic perspective. The "argument" is as follows and we will now see why it is important for us to have forgotten about Descartes meditation and the underlying assumptions associated with it which would affect our understanding of what Avicenna is trying to say:
So we say that it has to be imagined as though one of us were created whole in an instant but his sight is veiled from directly observing the things of the external world. He is created as though floating in air or in a void but without the air supporting him in such a way that he would have to feel it, and the limbs of his body are stretched out and away from one another, so they do not come into contact or touch. Then he considers whether we can assert the existence of his self. He has no doubts about asserting his self as something that exists without also [having to] assert the existence of any of his exterior or interior parts, his heart, his brain, or anything external. He will, in fact, be asserting the existence of his self without asserting that it has length, breadth, or depth, and, if it were even possible for him in such a state to imagine a hand or some other extremity, he would not imagine it as a part of his self or as a necessary condition of his self - and you know that what can be asserted as existing is not the same as what cannot be so asserted and that what is stipulated is not the same as what is not stipulated. Thus, the self whose existence he asserted is his unique characteristic, in the sense that it is he himself, not his body and its parts, which he did not so assert. Thus, what [the reader] has been alerted to is a way to be made alert to the existence of the soul as something that is not the body - nor in fact any body - to recognise it and be aware of it, if it is in fact the case that he has been disregarding it and needed to be hit over the head with it. (Avicenna, Al-Shifa: Soul, I.1 (Hackett Reader 178-9))
Here it is important for us to look at the key phrase in the flying man argument and understand what it is that Avicenna wants us to grasp, "...and you know that what can be asserted as existing is not the same as what cannot be asserted and that what is stipulated is not the same as what is not stipulated". For Avicenna, to assert that the self exists, that it is real, is not the same as asserting that square circles exist. Just as the world itself is exists and we cannot doubt that this is true, it is to be taken as evident that the self exists. Furthermore, in thinking of body parts it would not follow that these would naturally be connected to his self, nor would they appear to be necessary for his self to exist, for that is far from obvious that they do. Whilst it can be stipulated that sight would require an eye, or hearing would require ears, it is not stipulated that the self would have a body, even though, for the most part, we do have one. This is the crux of his floating man argument, the self or soul can be imagined abstracted from a body. The body is not necessary for the souls existence, though the opposite is true if we are to have a living animal or plant. For Avicenna, the soul is like a form, but the form is used in reference to matter and it is not enough, this soul he speaks of is a perfection of the body. Like a captain to a ship or a ruler to a city, each is a perfection of something though they are not the form of it. In this way, Avicenna wants us to know that a soul is the perfection of the body. It is "...a first perfection of a natural body possessed of organs that performs the activities of life."
To say that modern science has managed to map all 25,000 genes in the human genome, to be able to give a clear overall picture of the intricacies of human life, is precisely what Avicenna is not concerned with. In the same way that he discounts Aristotles First Cause as a satisfactory explanation for the existence of the world, so too is the explanation of causation for why living creatures differ from inert bodies. As we saw earlier, when Avicenna tells us "what can be asserted is not the same as what cannot be asserted", he is telling us that what we can claim exists without causing a contradiction is not the same as what would. Furthermore, that which we claim exists must be examined to see whether it is necessary through itself or through another and here we can use our imagination to see that the point in question is not about the set of events which led to the first flickers of life in some primordial mud millions of years ago, but as to the necessity of life itself and whether it was necessary through itself or through another for existence. If the causal chain of events which led to that particular point were themselves what resulted in the existence of soul in previously inanimate objects, then life is necessary through itself and there is no need to seek a soul to explain it. But that is to say that something is because it is, which is a circular argument. The only way out of this circular argument for a critic of Avicenna would be to begin the investigation by saying the following:
We commonly observe certain bodies perceiving by the senses and being moved by volition; in fact we observe certain bodies taking in nutrients, growing, and reproducing their like. That does not belong to them on account of their corporeality; so the remaining option is that in themselves there are principles for that other than their corporeality.
This is how Avicenna begins his investigation, and where the circular argument of those who deny the existence of a principle called "soul" eventually leads them. When Avicenna is telling us that this same principle is responsible for the issuance of any actions that "do not follow a uniform course devoid of volition", he is attacking the strict determinism which the proponents of a material and only biological view of life express. Avicenna is telling us that there is a principle which is beyond the material, beyond the formal which is inseparable from the matter, a principle that perfects life and makes it what it is - necessary. The "I" which is the subject of the flying man experiment is the first perfection of this complete unit of life. It has come to exist with the existence of the human body and the components of life necessary for it, but it then continues to develop and grow through its second perfection, "a body possessed of organs that performs the activities of life". The temporal cage within which this "I" grows to find itself becomes the very key which will allow it to reach beyond the temporal and grasp universals, the true objects of knowledge and philosophy.
The flying man argument is intended to remind us that we cannot know empirically what it is that makes living beings qua living beings alive necessarily. We possess this soul, on account of our intellect, at a level much higher than plants and animals. Avicenna gives us a crude method for experiencing what it is he is referring to through this simple thought experiment, which is not telling us much, nor is it supposed to. It is simply a pointer that would allow us, as fellow souls, to begin seeking questions higher than what can be answered through only a cursory reading of the input from our body's senses. Avicenna wants us to demand more from these bodies, to look further inwards to develop that innate "I" that we all experience and from which there is nothing to escape from. If understood in this more sobre light, where we succeed in imagining our souls existing separately from our bodies, Avicenna is successful in his goals and the flying man helps him to achieve this objective.
Ibn Sina, "The Soul I.1", in, McGinnis, J. & Reisman, D.C. (2007), Classical Arabic Philosophy: An Anthology of Sources, Hacket publishing Company, Indianapolis/Cambridge (Hackett Reader)