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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 about the entire situation/world around him?
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"?
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.
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 that negate the need to even remark on the possibility that this is all a dream.
The third assumption is that absolute necessity exists; it does not. Hume dispelled that idea in his An Enquiry Concerning Human Understanding and we haven't successfully refuted him since.
I hope I'm being helpful.
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.
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.
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.
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:
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.
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.
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.
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.
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.
Oct 29, 2014 at 7:10
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
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.
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.
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:
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:
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.
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.
How does one know one is not dreaming?
Different Understanding
This question may assert different understanding:
First understanding: The question asserts "How can we know that we are not placed on reality that are similar but fake?"
Second understanding: The question asserts "How can we know that we are not placed on reality that are completely different but fake?"
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"?
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
Automatic switching awareness by practicing "reality check" by someone else (expert)
Manual switching by ourselves
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.
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.
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.
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]:
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.
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.
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:
your sense of time is regular, and corresponds with the people and things in your environment;
you experience a coherent sense of reality, i.e. things and people look and behave normally or at least typically; and
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
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
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.
:)
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?
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!
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.
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.
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.
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.
