Today we have another post which falls into the realm of Philosophy of Science. An idea which makes us question our perception of reality, of our knowledge and consciousness. This is the sceptic’s favourite – the Brain in a Vat scenario.
Let’s explain what this scenario is before we branch off into the different variations and pass any judgement. The brain in a vat scenario is the scenario when an evil scientist, machine or other more powerful being than a mere human, has removed the brain from a human’s body and suspended it in a vat full of a concoction of organ-preserving elements. The neurons in the brain are then connected by wires to a ‘supercomputer which can deliver electrical impulses to the brain, ‘identical’ to those the brain would naturally receive when existing within a body which is interacting with an independent reality. At the end of the day that’s all our perceptions of the outside world are, a result of electrical signals travelling through neurons as a by-product of our experiences. Stroke a puppy, the fur of the puppy is felt on your fingers which sends signals representing the sensation of touch to the brain. Hear the puppy bark, sound waves resonate on your eardrums, which sends signals representing the sensation of sound. The idea is the supercomputer has the ability to simulate all these sensations and thus create the experience of a perfectly normal environment. In fact if so it could have even inputted in the sensory experience of all the other supposed human beings around you. This then resonates with the philosophical view of solipsism – one can only be sure of the existence of their own mind. (Wacky)
Now because this could be possible, the philosophical sceptics (people who like to question our very basic assumptions about reality) say, it is therefore impossible to tell from the perspective of the brain whether it is in a human body or in a vat. Now you may say woah wait a minute, think of all the neural simulations the controller would have to manipulate to construct a flawless reality – but unfortunately this is not the point. The sceptic’s point is that as sensations are just a product of neural signals, if even one can be simulated, theoretically they all can (with enough time). Therefore, as we cannot say with certainty we are not simply brains in vats, it is impossible to rule out being a brain in a vat. Therefore the bottom line is we cannot know whether our beliefs about reality are at all true.
There is an argument from biology that believes a brain suspended in a vat is fundamentally different to a ‘in-body’ brain and therefore we cannot say it is even possible to replicate the experiences. The ‘in-body’ brain receives input through the senses found in the body, which in turn receive their input from the external environment. However, the BIV receives stimuli from a machine. Whether these can be completely mimicked is highly debatably. This line comes down to the neuroscientists, of which one I am certainly not. However, to the best of my knowledge, those at the leading edge of the field do believe all experience can be expressed in electrical exchanges between neurons, and if that is the case the sceptic is right andit is impossible to rule out BIV scenario. I can sense many people up to this point will not be very convinced, let me try something more familiar to persuade you, something that everyone has personally experienced. Dreams.
The dream argument is the idea on frequent basis we believe we are in reality when we are not. When we dream, unless one is skilled in the art of lucid dreaming, we believe whatever we are dreaming about is in fact real in that moment. It is only when we wake up that we realise we had been deceived. Often in dreams we can also have sensory experiences, like the dreading one of falling. How do we feel this? Well it is a product of experience, we have experienced what it feels like to fall and our neurons can replicate those signals. You may think well surely we would have woken up to the actual reality by now, humans have been around for centuries. But it’s not humans we’re talking about its the experience of the individual which is in question, for we can never be sure of the experience of others and an individual of on average 30 or so human years – a mere blip in the lifetime of the universe.
All of this is all very matrix-esque, minds inside a simulated reality. Within our collective reality (if there is such a thing and we aren’t solipsists) then we are already pursuing an endeavour like this ourselves – virtual reality. As the progress stands now we are nowhere near making our attempts at virtual reality indistinguishable from the outside reality but it a task we are pursuing. Remember reading my article on the Fermi Paradox? Given the vast number of stars in the observable universe, statistically speaking there are a vast number of Earth-like planets. Our sun is relatively young and therefore other earth-like planets may host life/civilisations much more advanced than ours, due to their planetary system have been around a lot longer. Who is to say an advanced civilisation hasn’t mastered a virtual reality indistinguishable to reality already? An uncomfortable thought.
Another argument put forward for the scenario of the existence of brains alone is the weird and wacky Boltzmann brain paradox. According to thermodynamics systems tend towards a high level of entropy (a state of chaos) see ‘A descent into chaos’. Boltzmann proposed that the probability of fluctuations away from such high-entropy states are unlikely i.e. fluctuations towards order and organization. It’s rather unlikely a swarm of bees will randomly decide to form an ordered cube. Therefore, Boltzmann believes it is far more likely for the distributed matter in the universe to come together randomly to form a brain which is alone, floating around in space with a certain neural net representing memories, than it is for the existence of brains which came about through human beings. Brains as we believe them to exist arose from evolution from ancestors which required a high level of organisation in our external environment, i.e. earth, oxygen, food. ‘In an infinite universe, the number of self-aware brains that spontaneously and randomly form out of the chaos, complete with memories of a life like ours, should vastly outnumber the brains evolved from an inconceivably rare local fluctuation the size of the observable Universe.’ In a nutshell the paradox is that it much more likely that the brains that exist are Boltzmann brains, floating around freely as opposed to evolved brains in a life-welcoming environment.
[Futurama’s episode on Boltzmann brains!]
To summarise, philosophers argue that seeing it is impossible to verify that we are not just brains in vats or brains floating alone in space we cannot be sure that this is not what we are. (Take a moment to digest that philosophical point.) And, as such we cannot be sure if our perceptions of the environment are genuine representations of reality or a trick of our senses. Whether we should be so sceptical just because we cannot rule out the scenario is another question. It is undeniable that the philosopher’s point is valid but can it be truly be taken so seriously? Does it all even matter anyway if either way we still experience the pain of having to get out of bed to go to work in the morning?! I’d been keen to know what you think… provided you aren’t just a simulation within my mind of course. Drop a comment below!
An interesting and thought provoking post. If we are all BIVs, then I think it must be a very remarkable supercomputer contolling everyone (unless we have one each?) For example, humankind (or BIVkind) are continuously discovering new things. So how does it decide who will be the one to discover whatever – like Columbus sailing (maybe virtually) over to America…
Different people ‘discover’ these things and others may learn from it. A lot of people in the world may not even hear about whatever is discovered, and of course, nobody knows or understand everything. So it’s a very selective supercomputer that must decide who is going to learn what.
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Well it could work both ways – we could all be hooked up to the same supercomputer and able to interact (like in the Matrix) or it could just be that the individual is hooked up to a supercomputer and the experience of interacting with others is just one of the simulations. In the first case, yes selection would occur on behalf of the supercomputer in the second case it would just run somewhat like a pre-coded program. Thanks for reading!
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i had a friend once who got themselves in a real mess psychologically, because they did not believe this was what reality looks like, that it was actually particles dashing about, that reality looked like a fluid of some sort & that is how they wished to perceive reality in this life, so they agonized over this trick of the brain. i told them once that by wanting that they are missing out on reality as it is, whether it is right or wrong, it is something various & beautiful— it think i used that Bruce Lee apothegm, don’t look at the finger or you’ll miss all that heavenly glory.
i think of this as the same, if we are a brain in a vat, we have a reality of sorts & if there is nothing that can be done about it, give me ignorance, because as a brain in a vat i am not exactly in any position to alter my predicament. philosophers are daft sometimes. but so are scientists. & everyone really.
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Yes indeed, ignorance is bliss really would hold – if we know no other reality and there is nothing that can be done about it then many would say what is the point in dwelling over it. Others would object and say it is in the principle of knowing and/or questioning even if no action can be taken. Depends what camp you fall into I suppose..
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can’t fight a dichotomy, it never got us no where really, its fisticuffs are deft.
It is not I, that’s a simulation in your mind, it is you, that’s a simulation in mine. This will always be a fascinating debate, and so found this an enjoyable read, thank you. On a personal level, I feel it’s the fallibility of human kind, that exposes the reality of our situation i.e the unending product of evolution and not just a brain within a static computer program or vat. That said, if we’re all just a brain in a vat or part of a complicated computer program – with some sort of divine programmer at the helm – I don’t doubt he or she would be cleaver enough to make this program an evolving one. Ultimately it comes down to whether it really matters on any practical level or not, I do still need to get up in the morning, in an attempt to make some small alterations in the programming of my experiences. Hope you have a lovely day. א
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An interesting point. Though yes I agree, if they had mastered the ability to construct a flawless simulation quite likely they would be in the position to add little quirks to enhance its complexity. Thanks for your wonderful comment.
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I have thought about this many times for most of my life and have accepted as a workable hypothesis this final thought. As with all hypotheses it is tentative and useful and fragile to more useful approximations. Probability is a wild beast and cannot totally dismiss that monster under my bed each night reaching for my naked overhanging toe but I have learned to live with that suspicion and sleep pretty well at night.
This is where I live,
A place, situated
Five and three quarters feet
Above the street, or floor
Give an inch or more,
Thus placed behind my eyes,
Between my ears,
I exist to surmise
With what signals give
From nerve transmissions supervised
By genetics, peripatetics
Of this beast devised
By evolution’s solutions.
To comprehend what appears.
This brain, it’s plain,
Sits in divorce of light, of sound,
Of all that’s around, behind, above,
Touched only by the prompts of sensors
Specific to particulars of
Light, of sound, of touch and more
To be sorted, parsed, creating consequensors
Linking thinking, sinking
Into the morass of what to hate, what to adore
How to rate import, how to score,
Make use or abuse
Of the time to be alive
Or merely deny one must die.
This brain is not me.
In its constant fury to maintain,
Sustain vitality to just be,
Pump blood, air, gain
Nutrition, energy, entertain
To confront complexities
Of time and thunderstorms and snow,
Simply discovering how and where to go.
It assembled me as an implement,
An instrument to compass geographies
It has assembled from the tweaks and nudges
Of its fingertips and eyes.
I try to nullify surprise,
Plot alternates to disaster,
Secure my master.
I live and dance and delight
Amongst the fantasies
Of universe, of world, of day and night.
Of these glorious inventions
Out of fragments of sound and sight.
Realities, no doubt, are pluralities,
Trunking, branching, twigging
Immensely integrating possibilities
Of explorations and fertilities.
The mental halls of alls,
The palaces of time and space
Configured to contain within their walls
Things that are, that have been,
Sunshines of triumphs, midnights of disgrace.
People elsewhere smile at me,
The dead quite visibly still actively embrace.
Whatever might be in ubiquity,
This inner cosmos is my home.
A construct, personal, of desire, hope.
Expectation and despair
Subject to a need for constant repair
Where intellect can flounder and only grope.
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Another captivating poem Jiisand – I do not think I will ever have the linguistic ability to string words together like this!
From a practical view point, we can not prove the negative. The reality is that we have evolved to an extent whereby we can contemplate this state of existence. A brain in a jar isn’t much to look forward to! Still while there is life there is hope!
Yes we cannot practically prove it, we also cannot practically disprove it and therein lies the conundrum. Thanks for stopping by!
Great article! I came across this topic when reading on the realism-antirealism debate. I found Hilary Putnam convincing (a great article: http://www.iep.utm.edu/brainvat/). Meanwhile I hold it with the pragmatic constructivists: We don’t need to speculate about truth. Much more important than truth is whether knowledge is viable (useful and able to survive when contested with experiences). From my point of view, there is one fundamental problem with the BIV idea which is the core of many realist and reductionist scientific misconceptions (as most prominently in neuroscience): The (isolated) brain (here taken as the location of “consciousness”) is nothing but an organ, one part of many that together make up a complex system like a cognitively skilled entity or any other “autopoietic system” (using Maturana’s and Varela’s term). Following system thinking: Whatever must be in that vat in order to make that thought experiment plausible, it must be a “system” with such a high degree of complexity that it comes close to “complete” organisms (for example a human), so that the thought experiment becomes meaningless.
The concept that a brain requires a body to make sense of its existence is one solution to a sensible logical explanation, but this perceived brain is only one small element in a very large universe and there has been reasonable discussion by valid scientists that the entire universe may be a hologram (http://www.independent.co.uk/life-style/gadgets-and-tech/news/universe-hologram-holographic-evidence-3d-astrophysics-university-of-southampton-a7553766.html) and the rather primitive idea that this piece of organic tissue is floating in a vat or a bucket or in some nerd,s bathtub is not the only supposition about unreality.
The BIV is an experiment inspired by the french philosopher René Descartes who claimed that the truth is only known by reason, senses can trick our representation of reality. But if the BIV is possible, I wonder if this brain can still have rational thinking and capacity of abstraction, if its neurons are linked to a super computer. This is where the experiment fails because the capacity of thinking (as a pure rational and abstract or conceptual kind of thinking) is still an in-body brain activity. Dualists or spiritualists like Descartes himself would point out the existence of a soul/consciousness “inside” our body which makes us made of 2 dimensions! I don’t know if one day science can track the process of an abstract thinking. As far as I know it is still impossible! Great post Mekhi
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Our brain is the most powerful machine in universe.
And we are also ,we humans.
Politics, of course, is off topic, but as an indication of the most powerful intellect existing in the universe, the current state of humanity is an indication not particularly complimentary to universal possibilities.
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this is a great post…my line of work is really extreme from this topic but now u got me thinking…my son gets me thinking most of the time because of his questions, now this idea got me really thinking…but whatever it is— i just wish that whether this BIV is possible or not– i just wish that it will do something to make most of my patients walk, do things on their own since the brain controls the body…
this is a very interesting topic….u really got me thinking now…although my line of work is extreme to this topic..i just wish whether this BIV is possible or not— i just wish that it will do something to make most of my patients walk and do things on their own…afterall the brain controls the body…😊
That the brain has great influence on the body cannot be denied but it is worthwhile considering that each human, and most likely many other animals, contain within their digestive systems various colonies of microorganisms which have a strong influence on many aspects of the brain. This microbiome has recently been discovered to vary from one individual to another even within the same species which indicates we humans are colonies of many types of microscopic creatures and they each contribute in their own way to human behavior, some of whom are dangerous and some who are vitally necessary to our survival.
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I have not heard this suggestion and we cannot prove it is not accurate, it reminds me of the hologram theory which is being taken more seriously these days. As Karl Popper pointed out we need confirmation , and therein lies the rub. That word reality is precious to the scientist so they will search to find out the truth. Thanks for a fascinating run down on what is possibly a true dream scenario.
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Yes one of Karl Popper’s criterion for a sound scientific theory was the ability to be falsified. If one adhere’s to this philosophy of science viewpoint the quality of the brain in a vat theory deteriorates completely. Whether I believe a theory should be able to be falsified by humans to be sound I am not sure. It seems rather anthropocentric to me… would you agree?
Karl Popper was a deep thinking and a fair man , so he did not rule out the usefulness of a hypothesis or that it may not mature into a scientific theory. A classic example is Freudian psychology which he regarded as a useful hypothesis. Nonetheless I’m sure Karl Popper was correct and his contribution to science was fundamental.
All well and good so far Mekhi, but what about information from immaterial sources? That is, data from ‘extra-terrestial’ sources or ‘other-dimensional intelligence’?
On Saturday I attended a meeting where delegates on one side of the large room stood around the walls but with eyes closed and facing the wall. The others then stood behind them one to one. The person facing the wall was to listen to the Lord God for information about His gifting upon, and the gender of, the person behind them! The lady whom I’d never met before was very accurate about me. (It was then repeated so all attendees tried the exercise and most were successful.)
How would the B-I-V notion explain this?
Those are very interesting results Richard. I think before that we draw any conclusions I would say we need to repeat this experiment with larger groups and controlled environments, see if the outcome holds!
Yes, it’s repeatable in view of the fact this was just one variant of many ‘activation’ exercises used on these mentoring days. (Statistically, results may be inferred from past activities of unknown average attendance, say 200 at each of 30 events.)
Experimental rigour of course isn’t easy in such situations eg. individual sensitivity and the Holy Spirit’s presence are not controllable factors, the last of which isn’t always noticed by those whom He’s not yet touched (ie born-again). It’s a gift for those who are ‘naturally supernatural’.
Nevertheless, the test for prophetical activity is accuracy and where this is by ‘word of knowledge’ (ie private information) it can be immediately validated or not and thus indisputable; whereas, predictive words need to be checked over time. That’s why I log ‘fulfilled prophecies’ (ie contemporary ones) as for example, about 2 dozen over 12 years on Britain leaving EU!
As intriguing as the contemplation of supernatural forces may be and as seductive as the possibilities may seem the advance of formal scientific knowledge has been accompanied with a total lack of indication of justification for the existence of the supernatural. Doubtless surveys of the beliefs of large sectors of the population indicate very firm addiction to beliefs in the supernatural and huge resistance to the acceptance of much of the basic principles which have been long accepted by scientists such as evolution and the quite extensive evidence of human influence of global warming. In this era when the basic survival of life on the planet is becoming severely threatened by these beliefs the critical dangers are becoming quite apparent.
I believe that the brain is the most complex creation in the universe. We could place black holes, dark energy, atoms or even red giants as inconceivable phenomena, but I think that the human brain is the most fascinating and complicated of all.
Perhaps so, of the phenomenon we know in the universe anyway. The number scale of neurons in the brain is thought to be on the same scale as the number of stars in our galaxy!
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You nailed it with the Matrix-esque analogy. Which highlights so many of the pitfalls and dangers of pursuing this path intentionally.
From a philosophical perspective, definitive arguments to prove or disprove that we are BIV’s become pointlessly circular. So, as an optimist, I’m going to choose to believe that we are still brains in bodies making the best of our messy oversized worlds.
I’m new here, but love the premise, and the thoughtful posts. Looking forward to following.
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You make a very interesting point, to dismiss the BIV argument on the grounds of optimism or utilitarianism. If one accepts a utilitarian viewpoint then one should behave as though the external world is real and dismiss the BIV. Because, if one believes the external world is not real, it follows that other humans and beings do not exist, and therefore they cannot be helped or harmed by one’s actions. Thus, if one behaves as though the world is real and it is not, one has not seriously harmed their own happiness or the happiness of others. However, if one behaves as though the world is not real (believes in the BIV) and it is, one’s selfish decisions can cause serious harm to the happiness of large numbers of people. So, the cost–benefit analysis favours belief in the external world’s existence! So basically if in doubt it’s best to act as though the BIV isn’t the case, as you say, as it will always bring more good to the world. Thanks for your comment, great to have you on board!
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The concept that we may be mere brains wired to some type of computer that feeds us impulses to simulate a false universe has many interesting implications but one must keep in mind that the brain is an organ that is designed by nature to respond to the various nerve complexes and sensing apparatus that is presumed to operate in a universe we accept. Occam’s law dictates that the simplest solution to a problem is the most acceptable and that viewpoint indicates that we do exist in the universe we perceive so the BIV theory is not entirely ruled out but its probability is minimized.
There are real life situations where the BIV is partially duplicated. People who have had a limb amputated can stil sense discomfort in the missing part since the nerve connections still can be stimulated and provide sensation of the ghost limb. The human organism is regularly deceived in films where the audience reacts to light patterns that duplicate, to even a minimum extent, real life experiences. Our senses coordinate to supplement each other and when those auxiliary backups do not match we can become ill. I well remember being aboard a troopship traveling to Europe in WWII and waking in the morning to severe sea sickness because the motion of the boat did not match the static immobility of the interior of the ship. Astronauts in orbit where there is no up or down frequently suffer space sickness. And sense apparatus can be trained to parallel stimulus and react to irrelevant stimulus as when Pavlov’s dogs learned to salivate at the sound of a bell. A good deal of useful social control is based on false stimulus as politicians and advertising executives well know and nature is very adept at all sorts of camouflage to protect its creations.
The common presumption that the consciousness is somehow in full control of the entire organism and it exists fully informed by the senses of the nature of the environment Is an illusion accepted by most of the world but a good analogy might be that of a captain in command of an artificial entity such as a nuclear aircraft carrier with the command room windowless but supplied with an intricate television system to keep him or her aware of the outside world. As well trained as the captain might be, it is the nuclear engineers and electronic technicians and the flight crews and even the kitchen staff and other maintenance personnel who really grasp the necessities of their skills and not only keep the ship operational but also inform the captain as to what they think is necessary. A living human body, of course, is far more complex that an aircraft carrier and the human input to the consciousness has far more different and powerful ways of influencing the consciousness of the nature of reality. So much so that the nature of human perception of reality varies greatly between even the most intelligent and aware people, not to mention the huge numbers of people totally unaware of available understandings nor the many ways they can be interpreted.
Hi Jiisand, very interesting comment! I don’t think Occam’s law applies in all situations – nor should it be considered to be a rule, but rather a way of thinking that says we should accept the hypothesis with the fewest assumptions. Now whilst I agree that simpler theorems are preferable to more complex ones, and one may come up with an infinite number of other theorems which are not falsifiable but plausible I don’t think we have that exact scenario here. As the present moment in time, 2017, we do not have a wealth of theorems that give an all encompassing view of lifes big questions, as such I am not so sure we are even in a position to looks for the “simplest”. I think we would need more choice before we apply the razor. Don’t get me wrong – I don’t think BIV is reality, but it is certainly a fascinating idea which can shape the way we look at the world. Much in the same way that Schrodinger’s cat (probably) isn’t actually both dead and alive – but it is a powerful tool to consider things.
I feel what you are saying with regard to the brain being able to give the sensation of lost limbs etc – in fact I think it is the control the brain has, and the processing of every single input and output that actually adds fuel to the fire of the theoretical possibility of BIV. A lot of it comes right back around to the study of consciousness. In all honestly until we as a species have a good and accurate description of what consciousness actually is, it seems unlikely that we will ever be able to constuctivley argue for or against alternative theories like this.
One of the cleverest and most fascinating illusions that has been bestowed to every conscious being in the universe is that each one lives in the universe which encompasses us all. To understand the basis for this complete misunderstanding is to realize that the reality which each one of us accepts is a creation out of necessity so that each form of life can survive and proliferate. What we designate as the consciousness must acknowledge just those inputs from the massive possibility of inputs from the external world to react to those basic necessities. It is the function of the sense apparatus plus the subsequent neural processing equipment to discriminate amongst the massive input and choose only what is vitally necessary to exist. There is no doubt that the activity of the universe offers far more information than even the basic senses can discover. The light and the sound and the touch and whatever other senses that have developed and can sense is only the tiniest fraction of what is available and even this is far in excess of what is necessary for survival so the various successive stages of processing this sense input passes through successive nervous centers that discriminate and eliminate that which bears little or no import to the final compilation that the brain makes of what must be acknowledged, understood and reacted to. That final compilation is where the consciousness exists and what is accepted as reality. Since each species and even each individual within each species has been conditioned by genetics and experience to be more or less aware of the intensities and importances of even the severely shorn final results of the combined sense inputs, the raw material for the constructions of the various internal mosaics of each individual’s reality can vary tremendously.
Humans have been extraordinarily clever in extending their sense apparatus from microscopes to telescopes to robotic devices that can explore the solar system and beyond and mechanisms which can deal with masses of information to expose unexpected relationships so that our internal configurations of what we consider reality have been considerably extended. Nevertheless, the possible information to explore and incorporate into our understanding most probably remains minuscule compared to what may be yet to come and there remain suspicions that much information will always be beyond our reach.
In my own experience as to the illusional quality of my own reality I have noticed that when I watch the motion of individual clouds across the sky, if I stare for a few moments I see that the clouds do not move smoothly and continuously but move a short distance and then stop momentarily before they move again. I am fully aware that the winds that move the clouds cannot be other than continuous so this stopping and starting must be an illusion that my processing of sight functions to create a picture which can be further processed to move a bit and then pauses to reprocess the new input that can be moved a bit further. I have asked other people if they see this peculiar phenomenon and they claim not to so I am unsure if it is an illusion common to everybody.
I recently stumbled across this topic which was touched upon in Homo Deus by Yuval Noah Harari – a book which is absolutely mind-expanding…I highly recommend it!
He analyses all this in terms of algorithms, and makes the link between the organic algorithms inside us, that allow to create our reality, and the algorithms which drive much of technology, and how the future may see these merge in a variety of (slightly unnerving) ways.
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This does sound interesting – i’ll try get hold of a copy, thank you!
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Yeah this is one of those timeless questions in philosophy and psychology. Anyone interested in the related psychodynamic aspects should look into what existential psychologist Irvin Yalom has to say about what he calls “existential isolation”. I’d post a link but I’m too lazy.
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Pragmatically, it makes no difference. The reality you experience is the only one you get. Unless skepticism offers you a way of escaping the vat (or the solipsic dream) it serves no purpose and you may as well assume reality is real. However, skepticism has come in handy throughout history when it is reasonable to question our assumptions, like the earth being the center of the universe.
The reality of our perception of reality is often tested, for example, when we walk into a glass door we thought was open. But, to the degree that our perception of reality works to let us deal successfully with it, then our perception is true.
Take free will for example. We empirically observe ourselves and others deciding for themselves what they will do. And we also empirically observe cases where someone is forced to do something against their will. The term “free will” is used to make this significant distinction. And that’s basically all it does and all it needs to do.
Mekhi, I agree with you that “the philosophers” are undeniably correct in asserting that we cannot know for certain whether a reality outside our minds exists. I further agree that has few, if any, day to day implications for most of us, although it may confound the fundamentalist preacher who wants to claim with absolute certainty that his or her god condemns homosexuality. Preachers aside, though, very little day to day application.
I do think, however, it might have application to the philosophy of science, and specifically to the question of, “What makes some method of inquiry ‘scientific’?” I would argue that, if we sufficiently examine that question in light of the problem, then we will eventually arrive at the insight that the sciences crucially — and perhaps even entirely — rest on the principle of intersubjective verification. Either that or we must indulge in metaphysical speculations about the existence of an external reality.
The reasoning is a bit too complex for a blog comment, but perhaps it can be summed up: If we cannot know for certain whether a reality outside our minds exists, then in the absence of any metaphysical speculation that such a reality does indeed exist, we are reduced to intersubjectively verified “facts” in the sciences as a replacement for the notion of independently existing objects.