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How could one logically demonstrate to someone skeptical that one is "really" there, and awake, and not just dreaming about the entire world around them?

Which philosophers or philosophies have addressed this problem of how one knows one is, or is not, dreaming?

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    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]: iep.utm.edu/brainvat [2]: plato.stanford.edu/entries/brain-vat [3]: en.wikipedia.org/wiki/Brain_in_a_vat#In_popular_culture
    – jimjim
    Jun 10, 2011 at 3:31
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    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: - wright.edu/cola/descartes/mede.html. In addition, the Stanford Encyclopedia of Philosophy article on Descartes' epistemology has a particular section that c Aug 9, 2011 at 21:19
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    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.
    – user34482
    Aug 2, 2019 at 12:36
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    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" Aug 16, 2020 at 8:20
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    A very common theme in some of the above comments is “we can’t know anything with certainty”. This could be relevant as a single comment, but it still would be much better to analyze the specific epistemological characteristics of dreams, not just uncertainty in general. This resource appears to have been neglected in the decade+ this question has been here: plato.stanford.edu/entries/dreams-dreaming Dec 26, 2023 at 23:36

26 Answers 26

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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 refers to private, inner sensations. 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 targeted 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.

These are anti-skeptical arguments, which apply equally to the claims that we are dreaming, deceived by a demon, or that we are a brain in a vat. They are effective in proving that any language user cannot have always been dreaming, always deceived about the reference of their 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.

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    What prevents a non-language user to dream of a language user? If nothing, then a person could be dreaming entire world which includes the conception of "me" who interacts with "others" through a language concocted in the dream.
    – tejasvi88
    Feb 26, 2023 at 6:54
  • @tejasvi88 I think that invites us to differentiate between actual dreams and philosophical dreams. It is (arguably) unlikely a person who never learned language would dream of a person using fluent language. The “philosophical” conception of dreams is often used in thought experiments, and is basically any mentally generated type of experience, which the experiencer believes to be real; no matter how implausible actually having such a fantasy may be. Dec 27, 2023 at 0:07
  • I’m not sure this answer really answers the question. The main gist of it is two points: 1. “It would be impossible to refer to one’s own dream experience if dreaming was all one ever knew.” 2. “Any language user cannot have always been dreaming, for language must have been learned in a shared environment.”. Put simply, “Assuming Wittgenstein’s premise that actual language necessarily implies the existence of multiple consciousnesses using it, if someone is using actual language, then by definition, multiple consciousnesses exist (and hence the situation is not solipsistic). Dec 27, 2023 at 0:18
  • I think that core idea maybe could be developed into an answer to this question but it needs much more development to make a strong case for something. Dec 27, 2023 at 0:19
  • Brain doesn't exist. "Brain" is just an idea in consciousness. See my paper "How Self-Reference Builds the World": philpeople.org/profiles/cosmin-visan Apr 21 at 23:21
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+50

There are a variety of skeptical scenarios that undermine the claim that one possesses some kind of ordinary knowledge, such as the dreaming case, Descartes's evil genius, and the brain in a vat. These scenarios undermine basic claims that people ordinarily take to be obvious, like “I know that I have hands”. G. E. Moore has a lovely little paper called A Defense of Common Sense on this. 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 have hands. (Premise)
  2. I do not know that I am not dreaming. (Premise)
  3. I do not know that I have hands. (1, 2, Modus Ponens)

Moore turns this on its head:

  1. If I do not know that I am not dreaming, then I do not know: ”I do not know that I have hands.” (Premise) (In other words, when I am dreaming, I do not know what I do or do not know, since dreams undermine the possibility of knowing anything).
  2. I do know that I have hands. (Premise)
  3. Therefore, I know that I am not dreaming. (Modus ponens 1, 2) (In other words, the assumption that I know something refutes the possibility that I am dreaming.)

There are two interesting things about this argument.


The first is that it challenges the skeptic to give us a 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.

But Moore points out that the skeptic can't stipulate that nobody knows this, or the skeptic themself would have begged the question, of how anybody knows this. In other words, the claim nothing is knowable may be self-defeating, and may undermine itself.

So the skeptic needs to give an argument why nobody knows they have hands. Here's one thing they could say:

  1. For every person S, and every truth p, S knows p if and only if S is able to prove p. (Premise)
  2. Nobody can prove that he or she has hands. (Premise)
  3. Nobody knows that he or she has hands. (from 7, 8 by Universal Instantiation and Modus Ponens)

Moore agrees with (2). He isn't claiming that it is possible to prove that one has hands.

Moore disagrees with is claim (1), that something is knowable only if it is provable. Moore says that isn’t the case. There are things we know but can't prove, and that's 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 one such item of knowledge.

If I do know that I have hands, then I also know that I am not dreaming.


The second interesting thing is that Moore argues that it isn't a matter of choice whether one is going to accept common sense or not.

Moore's view is that every claim to knowledge - including the skeptic's claim to know that (1) is true - begins from common sense beliefs.

The question isn't whether we are going to accept common sense or not, but whether were are going to accept common sense and skeptical scenarios that conflict with common sense.

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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 that it is impossible to put them together into 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, I know from my interactions with people that they have experiences of the same kind as my own, both in dreaming and in waking life, which confirms my belief that dream consciousness is different from waking consciousness.

If this life is not real," it would have to be an extremely well-done and elaborate simulation, on the order of The Matrix, rather than merely a normal dream.

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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.

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  • OK... but they shouldn't need to cooperate that much.
    – wizlog
    Jul 19, 2011 at 18:16
  • (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)
    – wizlog
    Jul 19, 2011 at 18:17
  • 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.
    – Kalamane
    Jul 21, 2011 at 20:50
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+50

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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This answer is based on the following assumption: It is better to have experience accompanied by knowledge, than just knowledge. So lets try the following to (hopefully) gain experience. See it as me proving to you that you can discern between states of dreaming and states of wakefulness, I can't just do that with solely you reading text I typed, you have to do something. This is based on the assumption that reality is more than just intellect. The other (right) half of your brain is also involved in processing your reality, and that is the emotional/experimental aspect. So do the exercise below, please:

  • Close your eyes in a quiet place and think of how you want to feel and notice your bodily sensation.
  • Just keep thinking/feeling about it, you will start feeling it.
  • Your mind will wonder of (otherwise you are an super evolved mind already and you probably wouldn't be here). This is exactly like dreaming, you have lost control and are self-reflecting less. Angst/worries take away your focus: (thoughts about work, mortgage, a fight with your spouse, whatever).
  • Focus back on how you want to feel and notice your bodily feeling (changing) again.
  • Keep on doing this (and let yourself fall asleep).
  • Do this with a lot of will power for some time that feels right.
  • You will increase the frequency of self reflection drastically and you will likely wake up in a dream scenario one night where you gain conscious control of your environment to some extent, known as lucid dreaming.

This is something you can teach yourself, just like playing the piano. The point of this is that you self-reflect that you are not doing anymore what you want to do and get back at it. Google on "lucid dreaming and fMRI" and you will have biological evidence that areas in the brain of self reflection are more active during lucid(conscious/awake) dreaming, than non lucid dreaming. That your mind is wondering of is because the angst/anxiety is controlling you (or you let it control you). First you will experience those fears that are just beneath the conscious surface. The more you practice the exercise above, the more angst you will discover that lies deep down inside you. When you know/experience they are there, you can do something about it, recude them, and take control. Can you imagine, that those fears that live deep down inside you, that almost never get to the surface, influence very much of your daily life experience? As long as there are others things controlling you (or you are letting them control you) you have less control than you could possible have: you are dreaming.

This has thought me that I am dreaming often throughout the day, while almost anybody would say they are perfectly awake and not dreaming at all. That is because I am not skilled enough yet to constantly think about what I want and act upon that. The exercise above gives me more control of experience life because I can put more into it of how I want it to be, because of reducing the fears. I even start living at night: consciously experiencing the dream reality. Its starts with playing around (like children learn their environment) but it becomes more than that. You can really practice overcoming fears and use strong willpower (intention) to create what you want and see the effects immediately.

So the give one concrete answer to your question: You know you aren't dreaming in some aspect when you have consciously created what you wanted in that aspect that has created synergy (more than there was).

I use aspect because again, this isn't a binary state. It is not that you create all that you(with good intention) desire, or you create nothing at all. That would also imply there is an ending state. But combining stuff to create synergy is endless. It is fact you can create partially, step by step, what you desire: the house, spouse, children, work, quality time you desire, as long as it creates synergy. That is how your consciousness grows.

Look up things like:

  • My Big TOE by Thomas Campbell
  • Dalai Lama and what he has to teach.
  • Intention experiments on youtube or whatever.
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My whole use of the word "dream" -- probably yours too! -- comes from a lot of experience in which it referred to things that aren't like my current circumstances. I can't wish away walls (as Lennart pointed out); my memories of the recent past are relatively orderly; people and things aren't more likely to appear just because I've been thinking about them.

So under a theory of language where that matters, there's your answer: none of my training in using "dream" in sentences would license me saying that I'm in a dream right now, and I doubt many other people's would either.

The other obvious senses in which this might be a dream (maybe we're all trapped inside the Matrix!) seem to involve radical skepticism of a sort that would make philosophy pointless. That's not evidence for or against my life being a dream, but it does suggest a limit to how much energy it's worth spending on this particular skeptical question.

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    Perhaps, when you are "dreaming" in this dream you are actually "awake". The "strangeness" you feel when "awake" could happen because you are used to the physics and manifestations in your dream reality. Thus, your mind wrestles with awakening, "new" physics, and acceptance of the fact that your reality is not real.
    – Kevin Peno
    Jun 16, 2011 at 22:44
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Thomas Metzinger addresses some of these questions in his work, including The Ego Tunnel: The Science of the Mind and the Myth of the Self. The central question in that book is how the self, the apparently stable core of identity and consciousness, is constructed; that involves understanding what purposes it serves, and understanding situations of incomplete consciousness and identity, such as dreaming.

Most often, when we are dreaming, we don't know that we are dreaming, but it quickly becomes obvious to us when we are fully awake that we were dreaming. Metzinger spends some time discussing lucid dreaming, in which case someone is conscious that they are dreaming. He mentions in passing some techniques for increasing the likelihood of lucid dreaming: mostly developing routines of checking for inconsistencies in one's environment and in the sequence of events, in hopes of following one of these routines within a dream, noticing inconsistencies, and persisting in the dream while more conscious.

An idea Metzinger develops is that human consciousness and sense of identity is a model of reality that is actively constructing from sense data, checked for consistency, and with our physical sense of our bodily processes as a sort of carrier signal that allows for a central point of reference. Call this model-0; we are capable of creating alternate models, and comparing them to model 0, which both requires the ability to immerse oneself in alternate models and the ability to recognize which one is model 0; that recognition depends upon one's innate sense of their own body and their recognition of the consistency of experience.

I suppose you might imagine that there is a model -1, in which one is more conscious than one is in model 0, just as one is more conscious in model 0 than when dreaming. While I don't think this can be absolutely disproven, I would suggest that we can describe our awareness of our relative level of consciousness as a curved line that approaches a horizontal asymptote. Even in dreaming, when we don't realize we are dreaming, we know that continuity and consistency are lacking, and our sense of our own physical state is very distant, but these qualities can vary quite a bit even within a dream. When awake, we know our level of consciousness varies, but there is a much less dramatic difference in the range, and we know that when we are calm, well-rested, comfortable, and alert, we are about as conscious as we can be; we can tell by our own internal state that we're approaching that horizontal asymptote.

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  • The Buddhist state of enlightenment is described as being like 'awake' is to a dream, compared to everyday awareness
    – CriglCragl
    Apr 24, 2018 at 17:55
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We are constantly dreaming.

Our mind is a simulator, which tries to model reality using memory and the senses. When we are dreaming during our sleep, this simulator is running without real data from our senses.

It is necessary for survival that a minimal amount of simulation is present: if a lion roars we wake up, because the simulator must identify this, much like a sleeping computer with a screensaver, and power management is not completely shut off, because computers that don't flexibly change clocking frequency and disk readiness on touching the mouse won't sell better and their design won't survive.

The answer we know we are always dreaming is probably not what you seek. So to rephrase your question: how do we know that what we perceive corresponds to reality?

Consider the following example: you go out your house, your keys are in your pocket, do some things in the city, return home and find yourself locked out, your keys aren't really in your pocket, your mind misinterpreted your loose change for the keys and now has to remodel the past as you realize your mistake

There's different levels of reality, and it should not be seen as a scalar:

You can ask it as a binary question meaning: are my senses mostly suppressed and is my body in its resting state while it seems like I'm awake (what most people call dreaming). Then you'd probably want to consult lucid dreaming books with tips on reality checks.

Here seeing the mind as on or off is a first order approximation: you can realize you are dreaming and know that the real reality is different from what you experience

For the second kind of reality: it doesn't really hold as a property for your mind as a whole and much more refinement is needed: the belief that your keys were in your pocket was incorrect, so it's a per statement property.

Science can be seen as the simulator of all observations not just from human senses but also from measurement sensors, we try to interpret the data in multiple ways, and we sometimes find ourselves hampered by unsuitable frameworks. i.e. societies have actively dreamed of witches and hunted them down.

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    I propose that this direction of thinking will bear the most fruit over the historical position set by Hume. One of the points toward this end is that the goal for discerning between dream and reality is a critical element in the arrival upon a determination. Apr 15, 2013 at 2:22
  • +1 For pointing out that the first mistake is to see it as a binary state: wake/dreaming, as it is not. Atleast not to our experience. Indeed experience in lucid dreaming is a great advantage here to have the experience of different levels of reality. Oct 29, 2014 at 7:14
  • Yep. We may also literally constantly be dreaming in a very strong physiological sense. According to Rick Strassman 1) We metabolize DMT during internal visualizations and when doing 3D geometry. 2) It originates as the substance that initiates dreaming. So Terrence McKenna theorizes that this state of constantly dreaming is the origin of human intelligence as distinct from most animals. They only dream when they are sleeping.
    – user9166
    Oct 30, 2014 at 4:45
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Are we dreaming?

Case-by-case analysis.

Yes: Everything is a dream, ephemeral, temporary, constantly changing, and there is no inherent "existence" that is "radiated" by other "things" in this "world" (time x space) apart from our "own" mind.

No: This is not a dream, this is "real life" and independent of "mind" or "awareness" there will always persist an existence, which is generated by "others" in the environment, and no product of "personal" awareness/intelligence/sentience.

This topic is difficult to address with experimental science because we have affirmed some observer/observee obstacles to overcome in making experiments.

Generally: Science assumes that the human being is an unbiased, observer-on-the-sidelines, basically looking in through a window at "the world" and making talk of its "physics"

However, the view of the "observer" is actually biased, since the observer is necessarily part of the universe that s/he studies and observes. It is like a knot in the thread, trying to untie itself.

How can you understand, truly, if "you" is dreaming, or if "you" is part of a coherent, greater reality?

Well, you should not rule out the simultaneity of yes/no, and the non-possibility of simultaneous yes/no, either. These questions transcend the foundational assumptions of Science and Philosophy, and it is perhaps more intuitive to adopt a "flexible" set of fundamental thoughts, since it seems like we really want to talk about Awareness.

How Aware is one of a dream? You may be engaged in it quite forcefully, invested all your "chips" and have many Possessions, Achievements, Feelings and Thoughts all within this "sand box reality." Then, one wakes up and all understanding of gain, all benefits stemming from self-concern (concern for personal wealth, personal happiness) go poof. Gone.

The "memory" may persist, but in reality there was nothing "real" about the dream. Maybe it hurts to be apart from personal happiness, but really it shows something very interesting: Based on our observation of the situation, our feelings changed. If we could understand the deeper truth of how Dreams/Reality inter-played, perhaps we could understand more about how Reality/"Beyond" might inter-play. Since, if Reality is a dream, there should be something that transcends it in all directions... When one "wakes up", perhaps a similar "poof" may occur to all our cravings and attachments (all our foundations of personal/self-awareness).

We are constantly confronted with the self/non-self duality in daily life: we are a consistent, rhythmically breathing piece of the greater universe, yet we feel separated at large. Really, we observe from a "personal" point of view, but the universe itself is still greater than us all, and certainly contains "us". We are all of the same fabric, and all teammates playing for the same team. Perhaps it is a strange dream...

If it is a dream, how does one wake up? Well, this "awakening" is commonly referred to as "Enlightenment" and it is said to come from a deep inner understanding of the "true nature of things" -- to really understand yourself as a harmonious part of the universe, to not view others as "others", and to really come to grips with the transience/temporary nature of "life". One knows "Enlightenment" like one would know Hot and Cold -- it is perhaps one of the few desires founded on wisdom and it is the desire to "liberate the mind."

How does one get there? What does it mean?

Welcome to the Matrix, here are your introductory pondering questions; try and resist the urge to cover them with thoughts and words (be "silent" in there!), and let the "self" contemplate these things in the tranquility of the peaceful, unobstructed mind:

Everything changes. Nothing is permanent. Around you, there is infinite creation and infinite destruction in every moment.

Happiness is actually awesome. "I" strives to be happy and understood. True happiness comes from within, since all originates from the "mind" and this "observational" point of view. Consider that you can reflect negativity or happiness to the environment and those around you. Stuff you reflect gets reflected back eventually.

Continuity of the "one" object. We say the universe is made of pieces-parts, but really, you could never just delete a planet from the universe and still call it the universe. You'd compromise the "structural integrity" in a way, but really you would be changing a lot in order to make sure one planet got "deleted" because it's all part of one continuous flow, and you'd need energy that was somehow "extra" energy -- energy that was beyond all the types of energy our universe is used to. Something that could both ease the flow and "remove" things...

Divisions of objects/things: Every "object" that one can identify is just an agreed-upon convention for naming/communicating. Really, at any instant, you can't say that "you" is made of the same atoms, feelings, thoughts, or state of mind. Everything is in flux, so where is "you"? Where is any object? It is founded in the mind, and if you get good at watching/observing your own mind, you can start to understand the "formation" of desires and the "formation" of perception of objects (reification).

Understanding that the observer is still a part of the "observed" is a good place to start in trying to attain the insight you want, I think. Everyone's approach is different, although sometimes there is significant overlap in coming to "true understanding" between people and methods. Really, the process of living is finding out which method is right for you. If you hear something wise, and believe it to be so, do not discredit it due to the source. A dog's bark might enlighten you one day, you never know what your spark, what your trigger may be.

The more you contemplate it, the more you will be able to explain to others your ideas. Really, you should be patient until you feel like you've found the right question to ask. Even if you have access to omniscient wisdom, it's all about asking the right questions.

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How does one know one is not dreaming?

Different Understanding

This question may assert different understanding:

  1. First understanding: The question asserts "How can we know that we are not placed on reality that are similar but fake?"

    • This understanding asserts condition that generally know as false awakening state. It's where we were thinking on waking life, but actually we were still dreaming about our waking life.
  2. Second understanding: The question asserts "How can we know that we are not placed on reality that are completely different but fake?"

    • This understanding asserts condition that we are living on completely different scenarios of life and we are considering it is a continuation. For example: somehow we were awake and saw anything different and somehow we knew that might be it's because of an earthquake. The question is, are we living now at the same place or at different realm?
  3. Third understanding: Dream realm is something less real than another realm (that may be considered as real as it should be). Regarding to this understanding, the question may be interpreted as "How does one know one is not placed on environment that less real than what it should be"?

    • This understanding gives consequence, that even when we were succeed placed outside dreaming, again, we should ask, whether we are placed on different dream realm or we are now living on reality as it should be.

Continuation as It should be

The key to response these situations by understanding that:

  • Whether we are living on fake reality or we are living on something that less real as it should be (whether we don't know how for something must be considered as real as it should be), but one thing we have to be sure that there are continuations from our past life (past scenarios) to our current life (current scenarios).

  • Continuation as it shouldn't be, is the real fake living. Whether we always know that our life are entirely duplications but as long as our continuations are as it should be, then everything are as it should be.

Therefore, asking "how do we know we are not dreaming?" must be interpreted (equal to) as asking "how do we know that this current life is the real continuation from the past life as it should be?"

Different degree of comparison

"How do we know that this current life is the real continuation from the past life as it should be?" "How do we know that this current life is the fake continuation?

The essence is based on how far we can achieve the degree of comparison. This determines how far we can distinguish a fake continuations from the original continuations.

It can be provided by switching our awareness to get possibilities to know (make comparison) whether there are wrong continuations. And this degree of comparison to make comparison can be created through:

  • Automatic switching awareness by practicing "reality check" by ourselves

    • If we want to know whether this current life is fake, we must conditioning ourselves to always asking "whether this reality is fake", and when we are sifting to a different reality, our subconscious will remind us (automatic switching quickly) to ask (know, make comparison) whether this reality is fake or not. It will gain our awareness to make a comparison whether there is another reality other than what we are experiencing.
  • Automatic switching awareness by practicing "reality check" by someone else (expert)

    • If we want to know whether this current life is fake, we need someone else to sit beside us and ask to see whether there is unusual behaviour to our awareness that may endanger our life (by checking unusual pattern from EEG - ElectroEncephalographym) or whether we are living within dream realm too long enough, and further someone else may force us to awake (automatic switching) and may be it leads us to ask (know, make comparison) whether this reality is fake or not. It will gain our awareness to make a comparison whether there is another reality other than what we are experiencing, or we just simply awake from dream state.
  • Manual switching by ourselves

    • We can do manual switching from current operating system to the previous operating system or any kind of operating system by disconnecting our awareness manually from operating system through focus.

    Through focus, we can put our awareness at balance point where we can know (make comparison) that there are wrong continuation in this current life compared to unfinished tasks left behind within previous operating system.

    Practically, we can focus on something on dreaming, then (if we succeed) something that we are focusing on it, gradually will be changed or morphing and eventually will switch us into the waking state where we can deal with continuation as it should be.

The points are:

We can know whether we are dreaming or not by providing true comparison (not fake comparison) whether we are living with continuation as it should be or not.

  • It can be provided by switching our awareness through reality check or
  • Focus on something. Practicing meditation will help us to switch (escape) our awareness from current state of realities to different realm or to waking state, where we can deal with our continuation as it should be.

Without these, we may be drawn into fake believe (we believe that we are not dreaming, but actually we don't realize that we are still dreaming).

It's not about "we are not dreaming" or "we are dreaming", but it's about we are living with continuation as it should be or not. This understanding not only put us on awareness whether we are dreaming or not, but this understanding lead us to be open minded to accept any possible realities whether we are dreaming or not and put us away from fake responsibilities for others and for ourselves. It's the essence of living.

3

The other answers already discuss the relationship to other skeptical hypotheses, such as the one that I am a brain in a vat. It may be good to point out that philosophers have also argued that what we perceive around us may in a sense be real even if the skeptical hypothesis is true, for example this paper by David Chalmers. A related reference is JJ Valberg's Dream, Death, and the Self, in which he contemplates what we can learn about what we perceive around us and what we are by considering the dream hypothesis.

3

Henri Bergson (1859-1941) wrote about the problem raised in this question:

How does one know one is not dreaming?

In his book, The World of Dreams (1958), he stated:

Let us hastily extract from this lecture the basic difference between dreaming and the waking state. The same faculties function when we dream and when we are awake, but in one instance they are tense and in the other relaxed. The fullness of our mental life is in our dreams, but with a minimum of tension, effort, and bodily movement. We still perceive, still remember, still reason; all this may abound in dreams, for in the domain of the mind, abundance does not mean effort. What requires effort is precision of correspondence...The dreamer does not have the ability to make this effort. That is the one and only difference between him and a man who is awake.

From this basic difference many others could be deduced...[Notably]:

  • the incoherence of dreams

Since a dream characteristically exhibits, not a perfect correspondence but rather some variance between memory and sensation, quite different remembrances might be suited to the same sensation.

Thus often leading to a sense of absurdity.

  • the abolition of the sense of time

A dream can offer us in a few seconds a series of event which during the waking state would occupy whole days...In the waking state we live our lives in common with our fellow beings; attentiveness to this external, social bond holds sway over the succession of our internal states.

Bergson compared the lack of precision of correspondence normally experienced with the passing of time, to a clock without a pendulum. Lacking a regular sense of timing of events, the dreamer

...is no longer capable of the attentiveness to life necessary for regulating the inner according to the outer, for fitting inner duration perfectly into the general duration of things.

  • a shift from conscious to subconscious memories

Here, Bergson departed from the 'current' (1958) theory, that had us dreaming mainly about events that have especially preoccupied us during the day. He claimed that sleep filled with such dreams leave us exhausted, therefore it can't be normal or natural, since sleep is supposed to be recuperative.

In normal sleep our dreams relate rather...to the thoughts that have flashed by us like lightning or to objects that we have perceived almost without awareness. If we dream of events of the same day, the most insignificant facts, not the most important ones, will have the best chance of reappearing.

Bergson gave as an example of how we might dream about subconscious rather than conscious memories:

I was waiting beside the the tracks and was not in the slightest danger. Nevertheless, if the idea of possible danger had crossed my mind just as the streetcar came by...if my body had instinctively recoiled even though I was not conscious of feeling any fear, that night I might have dreamed that the streetcar was running over me.

So a skewed sense of time, an absurd feeling of incoherence, and a tendency to dwell on subconscious rather than conscious memories -- probably means you are dreaming.

Conversely (to answer the question directly), you should know that you are not dreaming if:

  1. your sense of time is regular, and corresponds with the people and things in your environment;

  2. you experience a coherent sense of reality, i.e. things and people look and behave normally or at least typically; and

  3. you have no trouble focusing on conscious memories, without the intrusion of predominantly subconscious ones.

The World of Dreams, by Henri Bergson (1958), pp 51-57

2

Zhuang Zi addresses exactly this question in his most famous "butterfly story", that goes in short like that:

"Zhuang Zi dreamed he was a butterfly enjoying its flight from flower to flower. After awake, he questioned if he was Zhuang Zi who dreamed of a butterfly, or if he was the butterfly, dreaming that he was Zhuang Zi. But between Zhuang Zi and a butterfly, he says, there must be some difference."

As you can see, he doesn't care to give a straight answer. You can live pretending you're dreaming. But probably you'll be taken as a fool, because between real-life and a dream "there must be some difference". Everyone knows it. We can guess most other animals know it too. It's common sense. It's (usually) necessary for survival. And you simply don't have to proof common sense. What needs proof is that which goes against common sense.

1

Bear with my only-slightly-and-probably-annoyingly-not-coherent rant here...

Logically, I don't think we can prove we're not dreaming. Interestingly enough, I've never wanted to prove I wasn't dreaming when I was dreaming, only when I'm not dreaming. (Of course, you could argue that I could have been dreaming when I thought I wasn't...)

As mentioned, our senses are deceptive and can't be used to really prove anything (except insofar that agreement on the state of something approaches unanimity.

Obviously there's a scientific proof that could be made, which of course hinges on the reliability of our senses in accepting scientific data, but if we accept that that data is correct, we could examine the state of our brain and "prove" that we are not dreaming. Keep in mind that science can't prove anything, and that whoever you were trying to convince that you were not dreaming would have to agree on the state of your brain.

Mentally, I think you could semi-prove to yourself that you are or are not dreaming based on the state of your brain. If I

  1. Make an assumption that X part of my life is not a dream...
  2. Label the current point in time "Y"
  3. Analyze mental patterns inside X
  4. Analyze mental patterns inside Y
  5. Compare X's patterns to Y's patterns

I can arrive at a scientific conclusion as to the dreaming state of my brain. Keep in mind that this relies on my ability to analyze those mental patterns, my capability of extrapolation, and the reliability of my analysis. Again, Science can't prove anything, so this is at best simply a way of convincing yourself, mentally.

Ultimately, I don't think there is any logical proof (i know, that doesn't answer your question. Sorry :) ) because the logic we're able to work with, at least as far as dreams go, relies on empirical data.

:)

1
  • OK... IF you can differentiate between the state of being "awake" and the state of being asleep and "dreaming" how would you tell which is which?
    – wizlog
    Jul 19, 2011 at 18:18
1

You can be fooled into thinking you are awake when dreaming, but you cannot be fooled into thinking you are dreaming when awake. When awake, the universe has a different feel to it. Whereas in a dream, them mind creates the illusion of something, in the real world the mind is experiencing what is there. I am not sure how we can prove it, but we do know it.

1
  • Touch your nose with your finger. If it feels right you are not dreaming. Describe what clothes you are wearing. If you can you are not dreaming.
    – gnasher729
    Dec 26, 2023 at 13:04
1

It is a difficult question to answer. Take for instance when someone who wakes from a dream gives an anecdote regarding what may have occurred within it, a common one for example, being flight. If we accept this anecdote we can then say that flying is something that one could only do in a dream since we are unable to do so while awake. In other words, there is room for one to conduct a comparative analysis as some people here have already mentioned and if there is no difference and all is the same then we probably would not be able to make any distinction to begin with that would enable one to pose the question. This may be a bit oversimplified of an assessment but I think it captures the essence of the point.

A precedent to dreaming would be "watching the back of your eyelids" for X amount of time. There is corresponding brain activity and even bodily reactions to dream events like "hypnagogic jerks" and sleep-talking that signify that a subject truly is "experiencing" something. So there is causality. When you think about it, all language utilized by subjects who generate an anecdote of a dream all signify various dimensions of space. If one states that they had taken flight then it must have occured within a space of some sort (or a "simulation" thereof?). If that is the case then one could say that they are occupying two spaces at once or are in a state of simultaneity: asleep in bed (space 1) and navigating throughout the Dreamworld (space 2). If experience of the latter were to leak into the former while you are awake then there would be a chance that you would end up becoming institutionalized if you were to lose the ability to distinguish one from the other.

All of this points at what would appear to be a violation of physics for one cannot fly here without an apparatus. But if there is nothing but physics how could this be? In dreams, if it is not of a memory that one relives then it is of a wish wanting to be fulfilled or the reification of some fear that one may have or maybe some combination of all of these in some elaborate abstraction. This would signify a relief or restriction of various degrees of freedom.

So, a question one could ask is: what is it that I am capable of doing in a dream that I otherwise would not be able to achieve while awake? If you can come up with an example or two then these would be indicators that would enable you to tell the difference between states that you find yourself in. Much honesty and scrutiny required in the process.

1

There are various mental conditions where we are deprived of our natural abilities, but this does not detract to the fact that we are normally able to tell whether we are dreaming or not.

This is an empirical matter. Either you are able to tell you are not dreaming or you are not, and which it is most plausibly depends on the nature of the human brain. If human beings couldn't normally tell they are not dreaming, the species would have long disappeared.

How exactly we are able to tell is a very interesting question, but you better ask a cognitive scientist, not a philosopher.

To understand the philosophical question, in the sense that it is asked here, requires us to accept the premise that when we have the impression that we are awake and not dreaming, we do not actually know that we are awake and not dreaming. This in fact does not make any sense. Dreaming and being awake are both entirely and solely defined by our own personal experience. Nobody is going to tell us what it is to be dreaming and what it is to be awake. Different people may have had different experiences of dreaming and of being awake, but it remains true that each person understands these two states on the basis of their own personal experience of them. So asking if we may be unable to tell one from the other is absurd.

The question is philosophical only in the sense that answering it requires to think about the fundamentals of human cognition, but it is in essence a metaphysical question. We may just as well ask how we know that red is not green and green is not red. But why stop here. How do we know that what we all take to be colours are not ham sandwiches? And so more generally, how do we know anything?

The fallacy, then rest on the idea that knowledge is what Russell called knowledge by description. According to the theory of knowledge by description, a description is knowledge if it is somehow true of the real world. Knowledge by description probably doesn't exists but this is beside the point. The point is that what Russell called knowledge by acquaintance isn't knowledge by description. In the case of knowledge by acquaintance, there is simply no description, and therefore there is no description that could be true or false of the real world. In other words, it would not make sense to ask whether what we know by acquaintance may be false. It would also not make sense to ask whether what we know by acquaintance may not be a fact.

We can always muse that we are totally deluded as to what we know. Once we exclude knowledge by description as irrelevant, what is left is knowledge by acquaintance, and knowledge by acquaintance is self-evident. We know pain as pain. We know redness as redness. Pain is what we know as pain. Redness is what we know as redness. Could that be delusional? No. We may be deluded about the impression we may have that the redness we experience is the colour of a particular object, say, the cover of a little book, but redness stands for itself and pain stands for itself.

So being awake is precisely what it feels like being awake and dreaming is what it feels like dreaming. Other mental states, such as lucid dreaming for example, are something else. Humans may delude themselves in believing that "real life" takes place when they are awake, and they may delude themselves in believing that what they experience in dreams is not real. Yet, we defined reality itself as what we experience when we are awake. Being awake is itself defined by what it feels like to feel awake.

Human cognition does not consist in recognising pre-defined objects, entities or states. We don't start life by trying to decide which is being awake and which is dreaming. We experience both states and what we experience comes to define our experience of reality.

How do we know that what happens when we are awake could decide of our own personal existence, while what happens in a dream does not? Strictly speaking, we don't. We just come to infer that this is the case from experiencing both being awake and dreaming every day of our lives.

We know when we are awake because being awake is different from dreaming.

1

First we need to define what is reality? There are many ways to define reality but I will focus on contact. When we touch iron rod it feels real. It feels real because of the pain it can cause if the solid rod is pushed against your hand. In an extreme case if I thrash you with iron rod then will you not call it real ? The nature of contact with iron rod changes from feeling solid to feeling painful. Clearly because it can cause pain we define iron rod as real. However like all contacts , the contact with iron rod is impermanent. Contact arises , changes and vanishes. In other words the contact with iron rod may end up feeling like a soft butter. If this happens then the reality seems to break down and the reality appears like a dream. This is the right conclusion. Reality is like a dream but it is only like a dream and not a dream itself because contact is impermanent. Contact becomes real sometimes and sometimes dream like. In other words sometimes dream becomes real and sometimes real becomes dream like.

Given the above observation we can say that we can not absolutely prove that reality is a dream or dream is a reality.

1
  • 1
    While I've upvoted this for the last paragraph, I'd like to point out that if you dream of your harsh school teacher thrashing you 25 years after you've left school (in the waking state), it would feel just as painful (in dream) as the rod in waking
    – Rushi
    Dec 28, 2023 at 5:48
1

According to Bertrand Russell in his book Human knowledge one cannot prove one is not dreaming:

It may be said that, though when dreaming I may think that I am awake, when I wake up I know that I am awake. But I do not see how we are to have any such certainty; I have frequently dreamt that I woke up; in fact once, after ether, I dreamt it about a hundred times in the course of one dream. We condemn dreams, in fact, because they do not fit into a proper context, but this argument can be made inconclusive, as in Calderon's play, La Vida es Sueño (Life Is a Dream). I do not believe that I am now dreaming, but I cannot prove that I am not. I am, however, quite certain that I am having certain experiences, whether they be those of a dream or those of waking life .

2
  • +1 Some typo?? "after ether"
    – Rushi
    Dec 28, 2023 at 8:44
  • Anyone who's experienced 'recursive dreams' ie repeatedly awakening from nested dreams can recognize the profound truth of Russell's point
    – Rushi
    Dec 28, 2023 at 8:52
1

Since dreaming is just a creation of mind this can never be demonstrated logically that one is not dreaming. Similarly, the limitation of one’s waking state is known /realised only if one has ‘experienced’ the state of Turiya. Of course, even this waking state is not ultimate and has been the subject of Eastern philosophies for thousands of years.

Actually we talk about dream only in waking state. Since no one experiences all 3 STATES OF EXPERIENCE (WAKING, DREAM, DEEP SLEEP) simultaneously, what is common in ‘Waking’ State of Experience (Jagrat Avastha), ‘Dream’ State of Experience (Svapna Avastha), ‘Deep Sleep’ State of Experience (Sushupti Avastha), is the truth. Therefore, even if one asserts that he can express this idea in this way, it must ultimately be absurd.

https://www.indicamoksha.com/blogs/3-states-of-experience-waking-dream-deep-sleep/#:~:text='Deep%20Sleep'%20State%20of%20Experience%20(Sushupti%20Avastha)&text=So%20deep%20sleep%20means%20dreamless,sounds%2C%20colours%2C%20etc.)

0

I can't prove you're not dreaming. It's entirely possible at a particular time that you are dreaming. However, to say that you're dreaming all the time is a bad explanation. Everything that happens in a dream is in your head and is uninfluenced by the rest of the world to a large extent. So if you are dreaming all the time, then there are parts of your mind that act as if they are entirely independent of you. Every time you hear a piece of music you think you could not have produced, or some scientific theory you think you could not have discovered, you must be wrong about that if you're dreaming. And every time you fail to foresee some problem, and you apparently struggle to fix it, really that problem was invented by you. And if you walk out into traffic the cars might not brake in time, but why not if they are just part of you rather than autonomous physical systems?

0

How do you know you aren't dreaming? You can't know, only I can know for myself if I'm not dreaming. Never run from a dream, the world's more pleasant in it. If I dreamed right now instead of writing this, I would be in a beautiful world of strange places, telling me of my knowledge and what I have to do when I wake up in the world I typed this. My dreams are my responsibilities, the think tanks for ideas and knowledge of reality. It thus came to me that all works out for the best, when I dreamed that this is a delusion, which means it's not. Therefore it's not a shock this world as long as it's a dream, don't be afraid to wake up, and don't be afraid to dream, I created the way things are felt, so I commit myself to this world as a world to never listen to people, haha, I'm ideal, since the pleasures is all that avoids pain, I will never listen!

1
  • What about nightmares?
    – CriglCragl
    Apr 24, 2018 at 18:14
0

If you need a proof on this question, then it's fair, on a wider scale, to say nothing can be proved at all. What can you prove if you have no postulates? Or in other words, what are possible postulates for this case?

In fact, no one has satisfactorily proved it through history.

On the other hand, people do say "life is just a dream". It's not just casual, it has serious implications, especially on the ground of multi-life/reincarnation hypothesis. But anyway it stays a metaphor subject to interpretations.

0

“How do you demonstrate to someone that you are awake and not dreaming”?

If you are dreaming then it doesn’t matter. If you are awake then there is nothing to demonstrate. The other person can see that you are awake.

But there are more mental states: Not conscious yet (newborn baby), dead, unconscious (anaesthesia or just knocked out), mad, or drugged. So you might need to convince someone that you are not mad or under the influence of drugs.

There are many cases (often violent offenders who claimed they were not responsible for their crimes) in institutions who find it very hard to convince their doctors they are not mad anymore, and many stayed in a mental institution longer than they would have stayed in jail.

0

I have significant tinnitus when awake. The tinnitus disappears while I am dreaming.

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