Wednesday, January 17, 2024

Avicenna’s flying man

Peter Adamson’s new book Ibn Sīnā (Avicenna): A Very Short Introduction is an excellent primer on the great medieval Islamic philosopher.  After a biographical chapter, it treats Avicenna’s views on logic and epistemology, philosophical anthropology, science, and natural theology, and closes with a discussion of his influence on later philosophy and theology.  Among the things readers will find useful is the book’s discussion of Avicenna’s famous “flying man” argument.  Let’s take a look.

The flying man thought experiment is one of the means (not the only one) by which Avicenna aims to establish the incorporeality of the human soul.  He presents it at the end of the first chapter of his treatment of the topic of the soul in his work The Cure.  One place you can find the relevant passage is Jon McGinnis and David C. Reisman’s anthology Classical Arabic Philosophy, which translates it as follows:

For the purposes of establishing the existence of the soul… [I]t 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 he 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...  Thus, the self whose existence he asserted is his unique characteristic...  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. (pp. 178-79)

The basic idea of the thought experiment is as follows.  A man who comes into existence in the bizarre circumstances Avicenna describes would have no sensory experiences.  For one thing, he has from the start somehow been suspended in midair, in a manner that does not involve even the air pushing against him – perhaps by miraculous divine action.  Hence he has never experienced external physical objects exerting any pressure on his skin.  Because his arms, legs, fingers, etc. are all spread out away from one another, he also has not felt even his own body parts pressing against him.  Because he is veiled (presumably in a manner that does not involve a veil making contact with his body) he has never seen anything.  Presumably his ears, nose, and tongue are similarly prevented from being affected by any stimuli.  Hence he has no awareness of any physical object, not even his own body.  As Adamson notes, while some might object that such a man would still have proprioceptive experiences of his limbs, it is not difficult to extend the thought experiment in a way that would prevent that.  We could imagine, for example, that the miraculous suspension of the normal operation of the relevant nerves is a further part of the situation. 

Now, the man would, Avicenna claims, nevertheless have awareness of himself.  He would know that he exists, even though he would not know that his body exists, and indeed would not know that any physical world at all exists.  In that case, though, he must be distinct from his body and from anything corporeal.  For if he were corporeal, how could he know he exists without knowing that anything corporeal exists?

Parallels to Avicenna?

I’ll come back to some of the remarks Adamson makes about the argument, but first let me make some observations of my own.  Avicenna’s argument might seem similar to arguments later developed in the Cartesian dualist tradition.  For example, in his Sixth Meditation, Descartes argues that he could in principle exist without his body existing, if God willed to create him that way.  And in his book Engines of the Soul, W. D. Hart argues that it is possible in principle for a person to have visual experiences while lacking a body, in which case it is possible for a person to exist without a body.

However, Avicenna’s argument is importantly different, in several respects.  First, Avicenna emphasizes that the man in his thought experiment has had no sensory experiences at all.  By contrast, Hart’s argument involves a disembodied person who does have such experiences.  And at least earlier in the Meditations, in Meditation One, Descartes suggests that it is possible for someone to have sensory experiences even in the absence of the existence of his body or of any material world at all, if a Cartesian demon caused a disembodied mind to hallucinate. 

Second, the key premise of Avicenna’s argument is epistemic, whereas the key premises of the Cartesian arguments mentioned are ontological.  Descartes and Hart start with the idea that it is possible for the self to exist without the body, and conclude from that that the self is distinct from the body.  Avicenna starts with the idea that one can know the self without knowing the body, and concludes from that that the self is distinct from the body.

Third, and relatedly, the thought experiments Descartes and Hart appeal to presuppose that the self could in fact exist apart from the body, whereas Avicenna’s thought experiment does not.  That is not to say that Avicenna doesn’t think the self could survive without the body, but only that that would be a further conclusion of the argument rather than a presupposition of the argument. 

The reason these differences are important is that they make Avicenna’s argument immune to certain objections that might be raised against Descartes and Hart.  First, one might question the assumption that sensory experience really is possible without a body.  If that assumption is wrong, then Hart’s argument will fail (though whether Descartes’s argument would fail will depend on how seriously Descartes wants us to take the Cartesian demon scenario).  But Avicenna’s argument makes no such assumption. 

Second, because they presuppose that it is possible for the self to exist apart from the body, Descartes and Hart might be accused of begging the question.  They are trying to get from the possibility of the self existing apart from the body to the real distinction between self and body.  But a critic can object that the claim that it is possible for the self to exist apart from the body presupposes that there is a distinction between self and body, and thus can hardly cogently be appealed to in order to establish such a distinction.  Avicenna is not open to such an objection.

If we are looking for arguments from the tradition that are similar to Avicenna’s, it seems to me that a more plausible parallel is to be found in some arguments earlier than his, which were developed by St. Augustine in On the Trinity.  Augustine held that the mind can know its own essence with certainty, but does not know with certainty that corporeality is part of its essence.  Hence, he concludes, corporeality is not part of the mind’s essence.  He also held that the mind can know itself without the mediation of any imagery, but cannot know material things that way, and concluded that the mind must not be material.

Augustine’s and Avicenna’s arguments are similar, then, in starting with what the mind knows or doesn’t know about itself and about material things, and from this epistemic premise drawing a conclusion about the distinction between the mind and anything material.  The key difference is that Avicenna appeals to a novel thought experiment in order to make his point about what the mind knows.

Some objections

As Adamson notes, one objection that can be raised against Avicenna’s argument would be to deny that the flying man really would or could know of his own existence.  One could hold that it is only after the mind has had some perceptual experiences that it comes to know itself, by way of reflecting on those experiences.  Note that one can hold this on the basis of the moderate empiricism of Aristotle and Aquinas, without committing oneself to the more extreme modern empiricism of Locke and his successors.  And as that indicates, one could hold this without rejecting Avicenna’s conclusion that the mind is incorporeal, but only the flying man argument’s particular way of arriving at that conclusion.

Adamson also notes that Avicenna’s argument has to be understood in light of his broader epistemological commitments, which include the thesis that the self is always at least tacitly aware of itself.  I find these broader commitments dubious, but for present purposes will simply note that the need to defend them in order to get the flying man argument off the ground at the very least makes it a considerably less punchy argument than it might appear to be at first glance.

Another objection noted by Adamson is that to know one’s self without knowing one’s body does not by itself entail that the self is different from the body, any more than the fact that Lois Lane knows that Clark Kent is at the Daily Planet without knowing that Superman is there entails that Clark Kent is different from Superman.  Adamson suggests that one way Avicenna could reply to this would be to argue that to know a thing’s essence, specifically, requires knowing its essential constituents.  If we say that the flying man knows his essence while not knowing anything about his body, then the body cannot be among the self’s essential constituents.

This interpretation of the argument underlines its parallels with Augustine’s arguments.  I refer the reader to my discussion of those arguments, which is not unsympathetic even though they are not my own preferred way of establishing the mind’s immateriality. 

Related reading:

Avicenna’s argument from contingency, Part I

Avicenna’s argument from contingency, Part II

Avicenna on non-contradiction


  1. Another objection noted by Adamson is that to know one’s self without knowing one’s body does not by itself entail that the self is different from the body, any more than the fact that Lois Lane knows that Clark Kent is at the Daily Planet without knowing that Superman is there entails that Clark Kent is different from Superman.

    I would suggest that Adamson's point here is strong, and can be clarified further by pointing out that "to know a thing" only requires knowing the thing in some (real) respect, not knowing it in all respects. A young child can know the concept of "tree" and correctly distinguish between trees and bushes, and still more know (vaguely and imperfectly) that deciduous trees are different from pine trees, but not be able to say precisely what the distinctions are that differentiate them at core, i.e. cannot articulate their essences. But he knows them, qua "trees" and as distinct kinds in some sense.

    Still more is all this true of the mind: it is as murky a subject as anything in this natural order. Just as all men know that they want "happiness", but there are a hundred different ideas on what happiness is, so also with the mind. We all know we think, but there is no agreement on what is thinking. Unlike with investigating physical things, we cannot lay out a thought for examination in the same way and subject it to rigorous testing: it doesn't "hold still" for measuring, analysis, experiment, or showing to others.

    The Greeks (and many other cultures) attributed the actions of poets to the influence of the gods in part because to be poetic is intensely unexaminable: it is (almost, if not absolutely) to destroy the thing studied to subject it to analytical examination (like dissecting an animal to locate it's "life"). At least this: while in the midst of the analytical examination, one is not enjoying the poetry in its native habitat.

    In similar vein: nobody has yet suggested how or where we first come up with the proposal of a thesis that might be proven by a syllogism if we can find the right sequence of premises to get there. Nor can we easily examine that process in which we first hypothesize a possible conclusion, before any effort to find a proof, it cannot be put under a microscope or in a test tube.

    The assertion that we know the essence of the mind is extremely dubious. For any Aristotelian, the idea is a non-starter: where Avicenna

    starts with the idea that one can know the self without knowing the body, and concludes from that that the self is distinct from the body.,

    Aristotle's thesis of what man's nature is (a soul/body union) is a thesis that man cannot be known properly without reference to body, the mere FACT of this disputed position shows that the nature of the mind is not manifest.

    Even if Avicenna were to rely directly on Augustine's list of mental operations that we are certain of performing, (understanding, knowing, willing, doubting, judging, etc), it is uncertain to what extent the list of operations unambiguously tells us what the mind is, without difficult analysis and fraught with the possibility of error. For a simple example: many people are either very uneasy with, or utterly reject, Aristotle's thesis that imagination is a different faculty from mind. But if that is in doubt, then you have to worry about whether your list of mental operations is complete and/or correct to get the "what it is" directly from that list. And surely modern mathematicians' (channeling Hume or Kant variously) utter rejection of the very category of "self-evident truth" forces us to accept that the list of categories of mental operations is in dispute.

    1. Josh Rasmussen's points on the "direct awareness" argument are relevant here, I think. Lois Lane is only indirectly aware of the substance that is Clark Kent/Superman; she is directly aware only of the image of a man who after all is different (someone with glasses vs someone with tights, which are different aspects).
      When it comes to our thoughts and feelings, we are directly aware of them. But we are not directly aware of our brains or other physical processes when we do so. This shows they are not identical, *even if* they happen to be two sides of the same coin. One side of the coin is heads and that is not identical to the side that is tails, which is why we can be directly aware of one side of the coin without being aware of the other side. They're different aspects.

      Just like one can argue for our thoughts and feelings not being identical to physical brain processes like that (even if they're distinct aspects of the same underlying substance), I think Avicenna and Augustine could probably use that for his argument, which is similar. The fact that a man can be directly aware of his self without being aware of his body shows that they are not identical, they are distinct aspects, even if they happen to be two different sides of a single object.


  2. WCB

    Such a man, a being, would known no language. Language must be learned. He could not think "I exist". If he has no sensations of things, no language, no sensations of his own body,would that man have any way of knowing he exists? The entire concept of existence would be utterly alien to such a being. Does anybody here remember anything from the time you were 1 day old?


    1. I think you would still be aware; you just wouldn't have a word for it.

    2. It's entirely possible that I was conscious the moment the sperm hit the egg, and have stayed that way ever since. I just don't have any way of remembering it.

    3. The sensory-deprivation experiments strongly suggest that a person put into a situation from the beginning with all sensory input blocked would be under great difficulties in learning to think, and he may well go insane quite quickly.

      Without sensory input, his internal flashlight of awareness would have no original matter to shine on, and it is not easy to say what his interior "conversation" would be about, without outside inputs and no past memories of them, nor past memories of concepts already formed. Take a flashlight that is "on" but has literally nothing in front of it to illuminate: are you aware that it is on?

    4. I always wondered why Avicenna asserts that such a mind would know of its existence. I mean, what does knowing even mean in such a state?

    5. @ René López
      I had a similar question below.

  3. I remember years ago in my atheist days, thinking that if sensory input, memories, and even discursive thinking were taken away, one could still be conscious rather than asleep. Thus, I figured that there must be a ghost in the machine.

  4. OP
    Descartes and Hart start with the idea that it is possible for the self to exist without the body, and conclude from that that the self is distinct from the body.

    I haven't read Hart, but if I understand Descartes correctly, his argument actually goes like this:
    a) If two things are identical or have no separate existences, we cannot define or conceive one thing without any references to the other.
    b) We can (at least Descartes can) define and conceive the soul without any references to the body.
    c) Therefore, the soul is distinct from the body.

    Thomas Hobbes objected by arguing that we could be wrong in our conception of things, and so even if we conceive soul and body as separate entities, it doesn't follow that they are separate in reality.

    Hobbes has a point, but the same can be said about human knowledge in general. Does our conception of a thing correspond with the thing in itself? How do we know? Descartes is dealing with the fundamental question whether it is possible to know anything with any certainty. In other words, if science is possible.

    To the extent we can know anything at all, I think Descartes' syllogism is valid. And I'm posting it here to see if anybody can poke holes in it. ;)

  5. Avicenna's flying man thought experiment reminds me of the passage from Hitchhiker's Guide to the Galaxy:

    "Another thing that got forgotten was the fact that against all probability a sperm whale had suddenly been called into existence several miles above the surface of an alien planet.

    And since this is not a naturally tenable position for a whale, this poor innocent creature had very little time to come to terms with its identity as a whale before it then had to come to terms with not being a whale any more.

    This is a complete record of its thoughts from the moment it began its life till the moment it ended it.

    Ah … ! What’s happening? it thought.

    Er, excuse me, who am I?


    Why am I here? What’s my purpose in life?

    What do I mean by who am I?

    Calm down, get a grip now … oh! this is an interesting sensation, what is it? It’s a sort of … yawning, tingling sensation in my … my … well I suppose I’d better start finding names for things if I want to make any headway in what for the sake of what I shall call an argument I shall call the world, so let’s call it my stomach.

    Good. Ooooh, it’s getting quite strong. And hey, what’s about this whistling roaring sound going past what I’m suddenly going to call my head? Perhaps I can call that … wind! Is that a good name? It’ll do … perhaps I can find a better name for it later when I’ve found out what it’s for. It must be something very important because there certainly seems to be a hell of a lot of it. Hey! What’s this thing? This … let’s call it a tail – yeah, tail. Hey! I can can really thrash it about pretty good can’t I? Wow! Wow! That feels great! Doesn’t seem to achieve very much but I’ll probably find out what it’s for later on. Now – have I built up any coherent picture of things yet?


    Never mind, hey, this is really exciting, so much to find out about, so much to look forward to, I’m quite dizzy with anticipation …

    Or is it the wind?

    There really is a lot of that now isn’t it?

    And wow! Hey! What’s this thing suddenly coming towards me very fast? Very very fast. So big and flat and round, it needs a big wide sounding name like … ow … ound … round … ground! That’s it! That’s a good name – ground!

    I wonder if it will be friends with me?

    And the rest, after a sudden wet thud, was silence.

    Curiously enough, the only thing that went through the mind of the bowl of petunias as it fell was Oh no, not again. Many people have speculated that if we knew exactly why the bowl of petunias had thought that we would know a lot more about the nature of the universe than we do now."

    1. As fun as this passage is, it is also highly unhelpful as an account of an interior process as an aware being begins to experience. If you have any experience with babies, and you watch them closely, you know that they don't automatically grasp the idea of naming, they don't immediately grasp an "I" that they could set apart from other things, they take a long time to integrate the different sense inputs into any coherent array, etc.

      What Adams has done is depict the initial experiences of someone who has no memory of prior experience, but has already developed the thought pathways of months or years of existence.

    2. That passage from Hitchhiker's Guide reminds me of some acid trips I took in the early 1970s when I was young and wild and foolish.

  6. I find this imaginary scenario to be very similar to the philosopical zombie one. In both cases all the behavioral criteria used for attributing a mind to a human being has been either denied or negated.

    Personally I find these imaginary scenarios to be unpersuasive. It is too easy to imagine things that are impossible.

    1. I agree. In imaginary scenarios that start out, if P then Q, and conclude, therefore S is true, what is the evidence that P is true?

      Another question: in order for the "self" to know that it exists, does it have to know that at least one other thing, that is not "itself," exists? How will the "self" formulate awareness of its own existence as existence if it has awareness of nothing else? I'm not formulating an argument here, only a "worry."

    2. Well, thought experiments just tend to be of that nature, whether it's Einstein's Twin Paradox or 'riding on a beam of light' or the like.

    3. WCB

      @Hal Friedrichs

      "Personally I find these imaginary scenarios to be unpersuasive. It is too easy to imagine things that are impossible."

      Bingo. This all turns into one big bull session. With careful BSing, one can conclude anything one wants. It can be fun until people start taking it all too seriously.


    4. What could be a more imaginative scenario and zombie inducing too than believing that you are "going to heaven" when you die. And, even more so, that you will be "bodily resurrected" when Jesus supposedly comes again.

    5. Yeah, understandably a lot of people aren't going to be swayed by thought experiments like this. The problem is that all we have to go on are conceptual analysis and thought experiments, because empirical investigation doesn't settle issues like this .

  7. Avicenna's thought experiment is no good because it presupposes what it sets out to prove (imagine: a thinking being who's aware of his own existence without proprioceptive phenomena. Therefore: it is possible to have knowledge of your own existence without proprioceptive phenomena.)

    The key to Avicenna's argument was that he was ignorant of proprioceptive phenomena. Proprioception was discovered by Charles Scott Sherrington in the early 20th century, many centuries after Avicenna flourished. Taking Avicenna's argument and then adding in "also let's take away proprioceptive phemonena from the flying man" as one of the premises results in the tautology A => A.

  8. What did Feser mean when he said free will doesn’t have to be conscious decision making, and can be like when you talk you don’t plan your mouth movements they just happen. How is that compatible with choice? Choices are planned, aren’t they?

  9. WCB

    The problem with free will is God's providence. God chooses the elect and thus the non-elect. Predestined since the beginning of the world. Or God does not distinguish past, present, and future. All is as it is. Your choices have been made for you. And more.


  10. relevant to all the folks here who find themselves opposing the argument: