How does one know one is not dreaming?

  • How does one know one is not dreaming? How could one logically demonstrate to a skeptic that one is "really" there, awake and not just dreaming the entire situation/world around him?

    Specifically what I'm asking is: which if any philosophers have addressed this problem of how one knows one is or is not dreaming?

    Which if any philosophies have attempted to evaluate the sense of claims like "I am not dreaming"?

    I think people want to close it because there is no REAL answer. There is no way to prove we are or aren't dreaming, just like there's no way to prove God is real or not real.

    There is a real answer: We can't. Posing the question implies that we can.

    @John There is no REAL answer to anything in Philosophy in so far as there is no agreement on what REAL even means.

    Why are people voting this down? It's a classic Phenomenology question

    I think the closed votes are based around the fact this is a fairly beginner question/concept in Philosophy, one addressed quite a few centuries again.

    @Wizlog you could reword it to "What ideas exist to prove we are not dreaming?" and probably get re-opened

    Why is this question closed ? This is the classic http://www.iep.utm.edu/brainvat/ argument,

    This is the classical Brain in a vat question/argument etc. instead of starting from scratch let's consider the existing bodies of knowledge : [stanford][2] , [internet encyclopedia of Philosophy][1] ,[wikkipedia][3] and then ask/answer a more specialised version of it. [1]: http://www.iep.utm.edu/brainvat/ [2]: http://plato.stanford.edu/entries/brain-vat/ [3]: http://en.wikipedia.org/wiki/Brain_in_a_vat#In_popular_culture

    @Chris S, I voted down because it's a classic irritating-question-professors-ask-their-non-philosopher-students, not a classic philosophical quandary. I cannot prove I am not dreaming, and the OP knew that when he asked the question. There is nothing useful to be discussed related to this prompt. Questions about skepticism and solipsism are relevant and interesting philosophical queries, but challenging us to prove we are not dreaming is a waste of time.

    I have attempted to clean up the question a little bit, I added a request for instances of philosophical analysis of the problem; I also tried to clarify it somewhat. Please feel free to improve further, or of course rollback if you feel I've misconstrued your question.

    If I am bored or my feet hurt, I am not dreaming.

    Easy. The answer is either: 1.The common answer: You cant know. This implies "You will know when you wake up." 2.You are always dreaming. You may or may not wake up, but this doesnt change the fact that you are dreaming. Whichever of the above answers you choose depends on your definition of dreaming, specifically if the definition of dreaming involves the notion of waking up.

    Easy. You ask on Stack Exchange.

    If we could know we're not dreaming (by some meaning of this word) then we could falsify Solipsism and Idealism and revolutionise philosophy. An example of an attempt to argue the point would be the idea of kicking a rock to prove it's real. In a recent issue of 'Philosophy Now' Prof Tallis argues that we can do it by staring at the back of our hand. Obviously this is not the case. It is a vastly important issue because if we could prove we are not dreaming we could dispose of most of religion and mysticism at a stroke, so our inability to do so is significant.

    @JohnM.- Just to cheer you up I'll say that many people would disagree with your pessimistic view of philosophy. You're just thinking of the philosophy you know, for which your comment would be true, but this is a local problem.

    This question seems to me just a great joke perpetuated by philosophy for far too long. How do you distinguish imagination from reality? They are just self-evidently different to the mind. How do you distinguish perception from dream? If they're two different states of the mind then they cannot be confused for one another. If they are the same state of the mind then they are the same REAL thing. The refutation is so simple I don't even know how philosophers can still debate this nowadays.

    I don't know how you do it, but a common method is to check whether the top stops spinning...

    Read Gurdjieff. He addressed that issue more than anyone. Gurdjieff invented a whole system of teachings to bring about the awakening in a human being. "Speaking frankly... contemporary man as we know him is nothing more than merely a clockwork mechanism, though of a very complex construction. A modern man lives in sleep, in sleep he is born and in sleep he dies"

  • This is actually an easier question than it seems, largely because it operates on assumptions that are easily conceded to or missed.

    The first assumption is that reality is absolutely compartmentalized; it is not.

    • Where does Greek end and Latin begin? That's a harder question than it looks like if you pay attention to language and there's a whole book dedicated to studying the indistinction between languages. It's called Echolalias.
    • Is Beckett's The Unnameable a book in the same way that Joyce's Ulysses and Nietzsche's Will to Power are books? Is an oeuvre everything a philosopher published or do notes and fragments count to? Are these easy questions? Nope, and these are just some of the unitary ideas Foucault pulls apart in The Archaeology of Knowledge. You could say that these details don't matter if this is but a dream, but then apparently at least your dream would itself call for these distinctions in mode of being, so being in a dream right now wouldn't matter.

    The second assumption is that perception must be observably identical in dream and reality; they are not. For every instance I ask you what you sense or remember in a dream, there are observable regularities that can be distinguished from the regularities of sense in waking life, lucid dreaming only exacerbating that distinction. Even if you're in a dream right now, then as far as your dream goes, there are two distinct realities which negate the need to even remark on the possibility that this is all a dream.

    The third assumption is that absolute necessity exist; it does not. Hume dispelled that idea in his Essay concerning Human Understanding and we haven't successfully refuted him since.

    I hope I'm being helpful.

    Your second assumption is really nice and **understandable**... Yet I've had some really realistic dreams, that I couldn't tell if I really was asleep or not... and yes, I do remember thinking to my self "am I sleeping". I do not understand what you wrote before the ";" in what you though is my third assumption.

    @wizlog Not being able to tell if you were dreaming or not is likely a memory error, not necessarily a flaw in observation.

    Didn't you mean "Enquiry"?

    @wizlog - But yet you realize that they're dreams, no matter how realistic they are.

    As someone that experiments with lucid dreaming quite heavily, I make it a point to look around and ask myself "does it seem like I'm dreaming?" multiple times a day so that I remember to do it when I am dreaming as well. I have vivid recollections of what I now know were dreams where I thought maybe I was dreaming, so I tried to find signs I was dreaming but everything was indistinguishable from reality so I decided I was awake. It's gotten to the point where life just feels like a perpetual series of dreams that I just keep waking up from and I honestly can't tell anymore.

  • We simply can't. We can't even prove that the Universe was created yesterday along with all memories of the past. We can't prove the Universe isn't just a run of a simulation (see the Simulation Hypothesis). If you put it this way, nothing can actually be proven.

    Not entirely true, as it could be proven that something exists. Cogito ergo sum, at least.

    so what? my point was that we can't prove we are not dreaming, or that we are not within a simulation. I never said either of those things do not exist.

    I think you should remove your last statement. That's a very different ball game from you can't prove that solipsism is wrong.

    @Bob, First and foremost, I think you should define what you mean by *"prove"*. What *is* prove?

    @JosephSpiros. Cogito ergo sum proves nothing, and in fact is wrong. It is **the** fundamental delusion of the mind.

    To know is not the same as to prove. We know many things we can't prove. We intuitively know, that's all. We gotta have some faith in our instincts, maybe that's what they call "illumination".

  • Two interesting arguments from recent decades relevant to this are Wittgenstein's Private Language Argument and the doctrine of Semantic Externalism.

    Wittgenstein argues in Philosophical Investigations that it is impossible for there to be a language which only referrs to private, inner sensations. Very roughly, the idea is that there is nothing which could count as misapplying a word used to refer only to an internal mental state. Correct and incorrect depend essentially upon external frames of reference as reflected in the responses of others. The argument is targetted at empiricism, but it is clearly applicable to the skeptic who claims we are dreaming, for it would be impossible, if Wittgenstein is right, to ever refer to one's own dream experience if dreaming was all one ever knew.

    Semantic externalism is a doctrine associated with Davidson, Putnam, Burge and to some extent, Kripke. This is the doctrine that it is an essential component of language that it is not an internal psychological state, that meanings must be grounded in a shared, external world. When you speak words I must take you as referring to something common to both our worlds, or else there would be no basis for successful communication. A shared, outer world is a precondition of communication. The idea is similar to Wittgenstein's.

    I have not presented either argument in any detail, but really have just sketched them in order to answer the question. They are anti-skeptical arguments which apply equally to the claims that we are dreaming, decieved by a demon, or are a brain in a vat. They are widely accepted as effective in proving that any language user cannot have always been dreaming, always deceived about the reference of his words, for language must have been learned in a shared environment. But the arguments cannot really show that I am not dreaming or hallucinating right now. They do however try to show that deception cannot be the norm.

  • Here's one way:

    DOOLITTLE But how do you know you exist?

    BOMB #20 It is intuitively obvious.

    DOOLITTLE Intuition is no proof. What concrete evidence do you have of your own existence?

    BOMB #20 Hmm... Well, I think, therefore I am.

    DOOLITTLE That's good. Very good. Now then, how do you know that anything else exists?

    BOMB #20 My sensory apparatus reveals it to me.

    DOOLITTLE Right!

    BOMB #20 This is fun.

    DOOLITTLE All right now, here's the big question: how do you know that the evidence your sensory apparatus reveals to you is correct? [...] What I'm getting at is this: the only experience that is directly available to you is your sensory data. And this data is merely a stream of electrical impulses which stimulate your computing center.

    BOMB #20 In other words, all I really know about the outside universe relayed to me through my electrical connections.

    DOOLITTLE Exactly.

    BOMB #20 Why, that would mean... I really don't know what the outside universe is like at all, for certain.

    DOOLITTLE That's it.

    BOMB #20 Intriguing. I wish I had more time to discuss this matter.

    DOOLITTLE Why don't you have more time?

    BOMB #20 Because I must detonate in seventy- five seconds.

    So now that you exist, prove your not dreaming.

    @Wizlog Descarte's counter-proof: if you didn't exist there would be nothing to deceive, or in other words you need to exist in order to have dreams. And one counter-counter argument: does there need to be a thinker in order to have a thought?

    There is really no coherent notion of "incorrect" sensory data. If there was such a thing, it would only be by receiving this "incorrect" sensory data that we could become aware that the sensory data was incorrect. So any purportedly "incorrect" sensory data would actually be correctly reporting the fact of its own incorrectness. The notion of "incorrect" sensory data is self-contradictory.

    @DavidSchwartz: It would be incorrect only in the sense that it does not accurately represent *the way things really are* based on some agreed-upon standard or consensus among individuals (which acts as a baseline).

    @stoicfury But that's logically impossible. If it didn't conform to some standard or consensus, then by failing to conform to that standard or consensus, it would be accurately reporting that failure. To fail to report an actual failure would be incorrect, but to accurately report an actual failure is *correct*, not incorrect. The concept that sensory data can be incorrect is only meaningful if you believe the sensory data is unreal or purely metaphysical in nature. If sensory data is regarded as part of reality (as it should be), then it always accurately reports reality, including itself.

    Oh I think we're talking about two different things. I thought you were referring to sensory data as it appears before one's mind, as opposed to the sensory data *in and of itself* (prior to being "sensed", which is itself an odd concept). Raw sense data can't be inaccurate, yes, but what comes before our mind isn't raw sense data, it's already been filtered by our senses and interpreted by our brain, and thus fallible. So I think we both agree. :)

    @stoicfury: I'm not sure what "fallible" would mean in this context. Whatever happened to it, that is what really in fact happened. By being what it is, in accurately reports precisely what actually in fact happened to it. It is in fact the end result of a perceptive/reasoning process and all it claims to be is precisely what results from that very process. Saying our senses can be fallible or erroneous is like saying a rock can be fallible or erroneous. Our senses report to us that which really is by being the part of reality we are in direct contact with. An "error" is logically impossible.

    @DavidSchwartz Ok, what you said doesn't counter anything I said, so I suppose we're in agreement. Yes, what comes before your mind is what comes before your mind... XD My only point was that it is not necessarily the same as **that which does not come before your mind** (collectively subjective reality) nor **what is** (objective reality). All three distinctions are replete throughout philosophical literature.

    Re: the original response, I think reaching for biology is a mistake by unjustifiably elevating it to a superior position it does not occupy (e.g. how does one know electrical impulses are the stuff of the senses without employing the senses?). You can only attempt to render the union of common sense/philosophical ideas about the senses and the biological contradiction free. Re: other discussion, the fact that we can distinguish between erroneous sense images and reliable ones, that we even speak about "collective subjective reality" assumes a particular, known objective state of affairs.

  • I'm not sure how nobody has mentioned this yet, but the most discussed philosophical work on the topic you have presented is Rene Descartes's Meditations on First Philosophy.

    The most relevant part of this work to your question is Meditation I, however, to be properly understood, it should be read in context of the complete work. Several full-text translations of Meditations on First Philosophy are available online at:

    In addition, the Stanford Encyclopedia of Philosophy article on Descartes' epistemology has a particular section that corresponds directly to your question. It is available online at:

    That *does* seem to be the most direct answer to "Which if any philosophies have attempted to evaluate the sense of claims like 'I am not dreaming'?" -- thanks!

  • G. E. Moore has a lovely little paper called A Defense of Common Sense that has important implications for your question. The basic idea is easy to grasp.

    There are a variety of skeptical scenarios that seem to undermine claims to possess some kind of ordinary knowledge. The dreaming case you mention is one such scenario. Descartes's Evil Genius case is another. The Brain in the Vat case is yet another. The kind of ordinary knowledge that these skeptical scenarios are meant to undermine are just basic claims that people would ordinarily take to be obviously true like ``I know that I have hands''.

    All of these arguments work like this:

    1) If I do not know that I am not dreaming, then I do not know that I do not know that I have hands. (Premise)

    2) But I do not know that I am not dreaming. (Premise)

    3) Therefore, I do not know that I have hands. (1,2 modus ponens)

    Now what Moore does is to turn this argument on its head. He argues:

    4) If I do not know that I am not dreaming, then I do not know that I do not know that I have hands. (Premise)

    5) I do know that I have hands. (Premise)

    6) Therefore, I know that I am not dreaming.

    Now, there are two clever things about this is this little argument of Moore's. The first thing is that it challenges the Skeptic to give us some reason why it was supposed to be true that we don't know we aren't dreaming. The skeptic would presumably say that Moore's argument begs the question, since the skeptic holds that a person cannot know that they have hands. However, Moore quite rightly points out that the Skeptic can't just stipulate that nobody knows this, or the Skeptic herself would have begged the question. So the skeptic needs to give an argument why it is supposed to be the case that nobody knows they have hands. Here's one thing a skeptic could say.

    7) For every person S, and every truth p, S knows p if and only if S is able to prove p. (premise)

    8) But, nobody can prove that he or she has hands. (premise)

    9) Therefore, nobody knows that he or she has hands. (from 7, 8 by universal instantiation and modus ponens)

    Now, Moore agrees with (8). He isn't claiming that it is possible to prove that one has hands. What Moore disagrees with is (7), the claim that something is knowable only if it is provable. That simply isn't the case, says Moore. There are things we know but can't prove and that's just a basic fact about the nature of knowledge. All of our knowledge of the world begins with our interacting with the world and gaining information by means of perception. Some of those beliefs we get about the world by perception are basic and simply must be correct, he calls these `commonsense beliefs' and says that ``I have hands'' is just one such item of knowledge. But if I do know that I have hands, then I also know that I am not dreaming, just as (6) says.

    The second interesting thing about Moore's position is that Moore argues that it isn't a matter of choice whether one is going to accept commonsense or not. Moore's view is that every claim to knowledge--including the skeptic's claim to know that (7) is true!---begins from such commonsense beliefs. So, the question isn't whether we are going to accept common sense or not, but whether were are going to accept commonsense AND skeptical scenarios that conflict with common sense.

    after all, it's just a counter-argument by resorting to common sense. Should it have been so complicated like a logic math? A better way may be just a plain talk about common sense.

    Should the first 3 be, "Therefore, I do not know that I do not know that I have hands." Or is the repeating of "I I do not know" an error?

    @user3559630 G.E. Moore has "unimpressed" me, and by referring to hands, twice this week on this site: https://philosophy.stackexchange.com/questions/51078/is-g-e-moores-here-is-one-hand-argument-a-bit-naive

    What Moore calls common sense sounds a lot like what Notre Dame's Alvin Plantinga calls a properly basic belief.

  • If I am dreaming now, then it is a much more coherent and stable dream than what I normally call a dream. When I wake up and think about the dream, I realize that locations, people, and circumstances in the dream were constantly shifting, and there it is impossible to put together a rational story. Sometimes I even notice these qualities while I'm dreaming, and I figure out that I'm in a dream. However, what I think of as waking life does not have those qualities. I can think back across the span of my life to my earliest memories and put together a narrative where one event leads to another, places are stable, and people move in and out of the story in an orderly fashion. Also, in my interactions with people, they appear to have experiences of the same kind as my own, both in dreaming and in waking life.

    Therefore, if this life "is not real," I would think it has to be an extremely well done and elaborate simulation, on the order of The Matrix, rather than something like the dreams I experience.

    +1 Chimes with my feelings: when I am dreaming I may "believe" it is real life, but when I am awake I "know" it is. Your answer explains why.

    I agree sort of, and I definitely know what you mean. However, it seems that dreams are mostly experienced as memories, and the experience of the dream itself doesn't ever seem to be '*present*'. My memories of what I *know* to be real apart from the present also have a fuzzy quality to them. They are never *present*. It is possible that a dream experienced in the *present* does occur in the same way reality does, but since they are only ever distinguished as dreams after the fact, they are always experienced as memories.

  • You want me to prove to a sceptic that I am not dreaming?

    Depends how cooperative they are:

    Do you agree that a dream is a fictional experience; one where someone (how about we call them a dreamer) experiences the appearance of reality, but there is nothing but that experience?

    That no object operates under it's own internal logic, but is simply a surface with no back to it, like an old-fashioned movie set, that has reality only as a direct experience?

    And do you also believe that it is possible to be unsure of someone else having a conscious experience separate from your own, because their mental experience is not directly accessible?

    If so then only one person can be in the same dream at once, because someone else's own experience of the world is not directly accessible, and so not part of that world of surfaces.

    Therefore if I am in a dream, you do not experience the world. And I'm not saying that your experienced consciousness is an illusion (whatever that means), I'm saying you're not seeing these words right now.

    If you are seeing them I am not in a dream you are a part of.

    (And bear in mind that then there is also the possibility that I, the person who is typing this, do not experience anything. I would disagree, but it doesn't matter, because as a person in your dream I would have no experience of your dream. I would still not be dreaming, not be a dreamer etc.)

    That's the sort of way I would go, but proving anything to anyone logically depends on what they already accept.

    OK... but they shouldn't need to cooperate that much.

    (A joke a friend once told me (even if not 100% true) was that if we were dreaming, we;d be able to come up w/ a better answer)

    After you said: "Therefore if I am in a dream, you do not experience the world. And I'm not saying that your experienced consciousness is an illusion (whatever that means), I'm saying you're not seeing these words right now." I would then add "Now punch your friend in the face. If you're dreaming, then they didn't experience the punch." This is why you'd need their cooperation.

  • from experience:

    the more control i have over my actions, the more toward the awake state i am (just because i 'know', or was fed the concept, that when awake, my world is reality).

    on the other hand, when i sleep, i have control of the world (with some training and not still at 100%) while my action just seem to 'flow' from somewhere, as i'm guided by something.

    it seems to me that the sub-conscient is dreaming (while i am active only when awake). in each world, we seem to trade place, one influencing the other while not directly capable of interacting with the world.

    i know that i am not dreaming now because, if i would be, i could change the world around be just with a thought.

    +1 (your new, and...) I'm not sure this would convince a skeptic, but I like the reasoning.

    `i know that i am not dreaming now because, if i would be, i could change the world around be just with a thought.` The thing is that it is exactly the opposite. When you are dreaming you have less control. When you are awake you gain more control. That you can't change the world around you with just a thought is THE indication that you are (partially) dreaming.

  • I absolutely love Kierkegaard's response to skepticism. To paraphrase, the problem is the abstract notion of certainty which doubt demands all be measured against. There is certainty that I'm not dreaming, but it's not like mathematical certainty or logical necessity... it's far more fleeting than that. The question "Could I be dreaming?" is a question asked in doubt. The answer Kierkegaard gives is that doubt cannot overcome itself:

    If I want to keep on doubting, I shall never in all eternity advance any further, because doubt consists precisely in and by passing off that certainty as something else. If I hold on to the certainty as certainty for one single moment, I must also stop doubting for that moment. But then it is not doubt that cancels itself; it is I who stops doubting.

    I get the sense that the later Wittgenstein and the ordinary language philosophers are of this school. They're not designing litmus tests of dreaming (private language), or "proving" that the fact of language means that we cant be dreaming, but to reveal those questions as absurd, and to bring us back to a position where thoughts of skepticism about other minds etc don't arise.

    The quotes are taken from a pseudonymous work of his, Concluding Unscientific Postscript, extract from Kierkegaard, Søren. The Essential Kierkegaard. Edited by Howard Vincent Hong and Edna Hatlestad Hong. Princeton, N.J.: Princeton University Press, 2000. pp. 221-222

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Content dated before 7/24/2021 11:53 AM