hello So today we're talking about philosophical skepticism and whether it's even possible to have knowledge see you might believe that you're watching a YouTube video right now but it's possible that that belief is false and instead your perceptions are just uh Illusions or hallucinations created by an evil demon so according to philosophical skepticism uh you could be being deceived by an evil demon or you could be in The Matrix or a simulation or you could be a brain in a jar being fed uh signals artificially and there's no way you'd be able to tell the difference and so if you can't tell the difference between the scenarios where all your beliefs are false and the scenario where you're in the real world and your beliefs are true then can you really be said to know anything at all and that's what today's topic is about it's about whether knowledge is even possible given the possibility of these uh skeptical scenarios [Music] [Applause] so philosophical doubt is not like the uh doubt we might have about things in our everyday lives if you left your house in a rush for example it's normal to doubt uh whether you turn the lights off before you left or if you can't remember your friend's birthday or you're not 100% % sure you might doubt whether her birthday was in August or September or if you're on the jury you might doubt whether the suspect really is as innocent as he claims and so when the evidence is incomplete or lacking like this it's normal to doubt your beliefs but philosophical doubt extends the reasons for doubting our beliefs uh beyond what would be considered ordinary so in the case of uh my friend's birthday in the ordinary context my doubt could be removed by say checking the calendar in my phone and when I see her birthday is in August the doubt is removed however in the philosophical context the doubt doesn't go away that easily so perhaps my phone has been hacked for some reason and they changed the date just to mess with me or maybe for some some reason my friend was lying to me about their birthday and they were actually born in January instead or maybe and uh here we go with the uh wacky philosophical thought experiments maybe I'm just a brain in a jar being fed electrical impulses artificially and so when I thought my friend told me her birthday was in August it was actually just you know these artificial IAL impulses and in reality my friend doesn't even exist and so my belief that her birthday is in August was false and so unlike the ordinary context it's not quite so easy to remove philosophical doubt because how do I prove whether I'm in the brain in of that scenario or I my friend really does exist and she told me that her birthday is in August the brain in a jar scenario is a classic if we assume experience is just electrial impulses generated in the brain then those same electrical impulses generated artificially would create exactly the same experience from your perspective as if what you were experiencing was really happening and so there's no way to tell from your perspective whether you're in the real world scenario or whether you're in the brain in aat scenario and your experence expences are being generated artificially if you've seen the film The Matrix um that's kind of what's going on [Music] there uh not that clip right now we're inside a computer program is it really so hard to believe so in The Matrix the machines enslave Humanity uh to use them for energy and kind of keep them enslaved by feeding them this artificial stimulus of a of what they think is a real life but actually is just basically a computer program another such scenario that people talk a lot about these days is the simulation hypothesis so given that computing power keeps getting better and better and with it our ability to simulate worlds keeps getting better and better then perhaps in the future we'll be able to generate generate simulations that have the same kind of fidelity as real life including Consciousness such as yours and mine and so if such a level of technology is possible in the future then it's possible that your experience now is actually just a simulation created by some you know nerd in the year 300 who wanted to uh simulate and experience what life in 2024 was like anyway the point of these skeptical scenarios at least for the purposes of today isn't to argue that these skeptical scenarios really are the case that we really are living in a simulation or that we're really just brains in a thatat or living in The Matrix instead the point of these scenarios is that they could be true and we wouldn't be able to tell the difference the possibility of these skeptical scenarios kind of pulls the rug out from under our ordinary ways of justifying our beliefs because I might think I know that I have hands because I can see that I have hands but that justification my visual perception of my hands is equally compatible with the brain inov that scenario as it is the real world scenario where I really do have hands and my hands are what cause my perception of my hands so the two sides of the debate today are this the global skeptic on the one hand says that because these philosophical skeptical scenarios are possible we don't know anything at all we don't know we have hands we don't know 2 plus 2 equal 4 we don't know anything and then the other side the let's call him the antiseptic non-septic the non-septic uh defends our ordinary knowledge the non-septic says that we can know that we have hands that 2+ 2 equal 4 and so on before the Matrix and computer simulations and all that there was dayart and in meditations uh dayut describes a scenario that serves the same purpose as these thought experiments a scenario where all your beliefs could be false and you wouldn't be able to tell the difference but before we get on to this most extreme sort of global form of skepticism dayart first goes through two kind of lesser waves of doubt the first wave of Doubt is illusion sometimes things aren't as they appear so if you remember from the knowledge from perception video uh we talked about a few Illusions we talked about how a squ where Tower might look round from a distance or the classic how a stick in water can look crooked when it isn't sometimes our senses tell us that something is one way but the reality is something different and so dayart says that because of this we can't always trust our senses but just because of Illusions we don't have to throw the baby out with the bath water we can still trust our perceptions a little bit says dayup because yes even though there are scenarios like the Crooked pencil where sense perception is inaccurate these scenarios are quite rare and specific these kinds of Errors says dayart don't give us reason to doubt all our beliefs they don't give me reason to doubt that I'm filming a YouTube video right now for example or in day Cut's case that he's sitting by the fire in his dressing gown however the next wave of Doubt dreaming gives me reason to doubt all sorts of things such as whether I really am filming a YouTube video right now when We're Dreaming we often don't realize that We're Dreaming until we wake up and so it's possible that I'm actually in my bed dreaming that I'm filming this YouTube video and so my belief that I am filming a YouTube video would actually be false this dreaming scenario uh undermines a lot of our justification for belief because for all you know you could be dreaming and you wouldn't be able to tell the difference but even in the dream says dayart there are still General things that correspond to reality such as uh colors shapes uh physical objects and so on even if these specific things We're Dreaming aren't real there are still General things that are common to both the real world and dreams that can't be doubted for example dayart says whether I am awake or sleeping two and three added together always make five and a square never has more than four sides so this brings us to decart's third wave of doubt the evil demon scenario and this scenario undermines even our most basic beliefs dayart imagines a being with the power of a God but who rather than uh using his powers for good as God would do uses his powers for evil to deceive you it's possible says deut that such a being has wished that I should be deceived every time I add two and three or count the sides of a square and this thought experiment can be extended to pretty much anything we consider to be knowledge so you think you know that you have hands well no you don't know that because you don't have hands you're just a disembodied mind and the evil demon was just messing with your perceptions and making you think you had hands or you might think I know that Paris is the capital of France but no says dayart you don't know that either because the evil demon was again just kind of messing with your perceptions France doesn't even exist let alone Paris and so that belief was false as well and again I know that 2+ 2 equal 4 I mean it's possible that the evil demon was messing with your mind every time you added two and two together and again the answer is actually five but the evil demons tricked you into thinking it's four and again with all these scenarios you wouldn't be able to tell the difference when your belief was true or when it's false and so whatever so decart's evil demon is a classic example of philosophical doubt rather than going through each belief one by one and doubting it that way which would take forever dayart instead undermines the foundations for all our beliefs by undermining the foundations of all our beliefs such as perception and thought the evil demon undermines all the beliefs themselves and raises the question of whether knowledge is even possible this position of global skepticism is where deut finds himself at the end of the first meditation he decides to treat everything that can be doubted as false and so the question is whether dayart can rebuild his knowledge or whether he's going to remain a skeptic forever so there are a number of different strategies the non-septic can use to defend our ordinary knowledge against these skeptical scenarios and a lot of these responses uh draw on topics we've covered in previous epistemology videos so you might be familiar with some of them already some strategies accept except that we can't conclusively disprove these skeptical scenarios but nevertheless argue that we can justify our beliefs and so possess knowledge other strategies look at the definition of knowledge itself and argue that according to these definitions we can still possess knowledge uh despite the possibility of these skeptical scenarios but the First Response we're going to look at decart's own response uh tackles the evil demon headon [Music] at the end of the first meditation dayart is in this position of global skepticism doubting all his beliefs because of the possibility of deception by the evil demon deart decid to treat anything that can possibly be doubted as false if you remember infallibilism from the definitions of knowledge video then that's the approach dayart is working with here in order for S to count as knowledge it must be impossible to doubt obviously infallibilism sets a very high standard for knowledge but dayart spends the next five meditations trying to rebuild his knowledge from the ground up using only the powers of his mind or intuition and deduction as we called it in the previous video so the first step dayart takes to rebuild his knowledge is the Kito argument so we talked a bit about it in the last video but just for a quick recap so so Kito Ergo Su is Latin for I think therefore I am and it's probably the most famous philosophical quote ever and decart's point here uh is that even if he is in the worst case scenario where he is being deceived by an evil demon and everything he's ever seen or heard has been a lie he can still be sure of at least one thing and that's that he exists because even if like I said the evil demon has deceived him in every way there has to be something that exists that's being deceived in the first place and so the very fact that deart is able to doubt his existence proves he does exist and so this is one way we can potentially reject the global Skeptics claim that we don't know anything deart would say at least at this stage we can be certain of at least one thing and that is that we exist but obviously I exist isn't much knowledge and so dayart spends the next few meditations continuing to rebuild his knowledge using only the most certain of logical deductions to do so so decart's next step is to prove that God exists and dayart gives a few Arguments for God's existence including versions of the ontological and cosmological arguments but we'll cover those in later videos instead uh I'm just going to quickly rehash the trademark argument for God's existence that we talked about in the previous video so in the trademark argument dayart says the cause of an effect must have as much reality as the effect in the previous video I used an example of a ghost to illustrate what I think dayart means by this if a non-physical ghost punched you it couldn't cause a physical bruise because the ghost has less reality than your physical reality so with this in mind dart's next point is that he is a finite and imperfect being he's a human being but says deot he is a being with the concept of God in his mind and the concept of God is the concept of an infinite and perfect being something with infinite reality compared to decart's finite reality and so given the previous point about the cause of effect must have as much reality as the effect then decart says the cause of this idea of God this idea of an infinite and perfect being something with infinite reality must itself be an infinite and perfect being and so an infinite and perfect being must exist and so God must exist so I exist and God exists and at least as far as dayart is concerned these beliefs have been established in a way that's impossible to doubt and so these are two claims we can use to reject Global skepticism then finally dayar argues given that God exists and given that God uh by definition a perfect being wouldn't be a deceiver then deart can trust that his perceptions of physical objects are accurate and that the external World exists so if dayart were to look at this Rubik's Cube or if I were to look at this Rubik's Cube I would form the belief that this Rubik's Cube exists but if the Rubik's Cube didn't exist and this perception was just you know an idea that was put in my mind by God say a bit like Barkley's idealism then that would be a bit deceptive because God is making us think the object exists when it doesn't exist but God isn't a deceiver God wouldn't allow us to be deceived in this way and so given that God exists as established in the previous trademark argument deart argues that he can trust his perceptions of objects and so with this deart has kind of restored the foundations of his belief he can trust his perceptions because he can trust that God wouldn't deceive him so it's a rather long-winded way of defending our ordinary knowledge but that's what dayart has attempted here uh deart has tried to provide a sort of chain of justification stretching all the way back from from our once uncertain perceptions all the way back to the firm foundations of certainty and so my belief that I'm not in some skeptical scenario such as the evil demon or the brain in the VAP can be justified and with it my ordinary knowledge can be justified dayart is probably right that if we can prove God exists then we probably can justify our perceptions and justify our ordinary knowledge but there all sorts of steps along the way where the skeptic might challenge decart's Arguments for example is it really true that the cause of an effect must have as much reality as the effect is it really so impossible that deart himself a finite and imperfect being couldn't have somehow come up with the concept of an infinite and perfect being by himself or is it really so impossible that an evil demon a less than perfect being could uh have put this idea of an infinite and perfect being in decart's mind as a sort of deception all these things really so impossible to doubt that we should say they are certain if these premises aren't certain then the skeptic can challenge decart's trademark argument and argue that he can't uh justify his perceptions because he can't justify that God exists and so we're back to square one we don't have any knowledge because we can't prove we're not being deceived What's the phrase uh hoist by your own pitard or creating a rod for your own back um I think that's kind of what dayart is doing in meditations because in demanding absolute certainty and the impossibility of Doubt for knowledge deart just makes it too easy for the skeptic to challenge his arguments it's just too easy to come up with skeptical scenarios however unlike that challenge decart's chain of reasoning here as we saw in the previous video with Humes Fork even the Kito argument I exist can potentially be doubted by skeptical arguments because it's conceivable and possible that you could have a thought without a thinker it's possible that perhaps the evil demon is just creating a bunch of disembodied thoughts that I exist but these thoughts are false because there's no eye there's no thinker of these thoughts and so although dayart seems to think he's defeated the skeptic um I'm not so sure sorry dayart decart's infallibilism perhaps concedes a bit too much to the skeptic we might argue that we know all sorts of things I know that Paris is the capital of France that I'm filming a YouTube video right now and that I have hands even if I can't be 100% certain of these things my belief here are justified by my perceptions I can see that I'm filming a YouTube video right now and I can see that I have hands and of course it's possible that my perceptions here are uh inaccurate because I'm in one of these skeptical scenarios but does the mere possibility of these skeptical scenarios really mean that my perceptions don't justify my beliefs whatsoever if you remember the veil of perception issue for indirect realism from the Knowledge from perception video we can adapt some of the responses to this argument to defend our ordinary knowledge against the skeptical challenge so you remember how lock argued that different senses confirm the existence of the same object if you see some words on a bit of paper for example and then you ask someone to read those words back to you the noises you hear them speak will confirm the same words that you saw with your eyes and so if you doubt whether the piece of paper with the words on it really does exist well you can confirm its existence with a different sense our knowledge from perception is Justified not by one single sense but it's corroborated and confirmed by multiple different senses and okay Lock's argument here doesn't prove with 100% certainty that these perceptions really do reflect reality but Russell would argue that the existence of Mind independent objects IE that perceptions really do reflect reality is the best hypothesis so when I look at and perceive my hands for example what's more likely that my hands really do exist and that it is these hands that cause my perceptions or that I don't have hands at all and that my perceptions are caused by something else well Russell argues that the simplest or most parsimonious explanation of my perceptions of my hands is that my hands really do exist and so while it's possible that I don't have hands the best explanation is that I really do have hands and so my belief that I have hands can be justified as the best explanation of my perceptions however the skeptic would probably reject the claim that the existence of my hands really is the best explanation of my perception of my hands after all the whole point of these skeptical scenarios such as brain in aat and the evil demon is that your perception would be identical in the scenario where you don't have hands as in the scenario where you do have hands and so the skeptic would argue that there's no reason to say one hypothesis or explanation is better than the other given that both both hypotheses are equally consistent with my perception of my hands as to Lock's point about the coherence and consistency of different senses well the skeptic could just argue that it's possible that the evil demon is creating uh coherent senses like this so when the evil demon deceives you about a visual perception of your hands he also accompanies it with say the tactile uh sensation of feeling your hands or if it's the brain in a vat scenario it's surely equally possible that the whoever is controlling these artificial stimuli just make sure that the appropriate sense experiences go together so when you see that you have hands you also hear that you have hands or can feel that you have hands and so the skeptic would reject Russell's claim that the existence of my hands really is the best explanation of my hands the skeptic would just insist on the original claim that there's no reason to prefer the skeptical hypothesis over the non-skeptical hypothesis because both these hypothesis are equally consistent with our perceptions and experience and again the problem reemerges if you can't justify that your perceptions are accurate then you can't justify any of the knowledge that comes from those those perceptions and so the Skeptics problem remains whatever the skeptic you know what I'm saying the Skeptics challenge we don't know anything basically a different tactic we might use to defend our ordinary knowledge against the Skeptics claim that we don't know anything is Barkley's idealist theory of perception so if you remember Barkley argued that everything we perceive receive and indeed everything that exists is just mind dependent ideas and that the idea of a mind independent objects such as a table or a chair is wrong everything is mind dependent or as he puts it to be is to be perceived if this idealist theory of perception is correct then the skeptic's argument never really gets going because these skeptical scenarios such as the evil demon brain in the vat and so on work by describing scenarios where your perception is one way and reality is another way so for example I perceive that I have hands but this belief is false because the mind independent reality is that I'm a brain in a jar being fed artificial stimulus to think I have hands however on the idealist account of perception such a distinction between my perceptions of my hands and the reality doesn't really make sense so according to Barkley's IDE ISM what my hands are just is the idea or perception of my hands and so it doesn't make sense to say that these perceptions are somehow inaccurate because again to be is to be perceived and so if idealism is correct the skeptic's argument where it's possible that your perception could be different from reality never really gets going because according to idealism perception is reality however for this response to work as a response to skepticism then idealism needs to be the correct theory of perception and that's Up For Debate I won't rehash the whole idealism topic again here but if you remember Illusions and hallucinations are one way we could respond to and reject idealism for example if idealism is correct and perceptions are reality then when I'm suffering from a fever or take drugs and perceive goblins on my sofa then idealism has the say that this perception is accurate that there really are goblins on the sofa because to be is to be perceived and perception is reality but this is clearly false there's clearly a difference between my perception where there's goblins on the sofa and the mind independent reality where I don't have goblins on the sofa of course idealism can and indeed Barkley does respond that hallucinations aren't really perceptions at all they are imaginations and products of our own minds um such as dreams but this just creates another opening for the skeptic because if it's possible to sometimes confuse perceptions with imaginations such that you can't tell the difference between perceptions and reality then isn't it possible that all your perceptions could be such imaginations if in the moment you can't tell the difference between a hallucination and a real perception then you can't justify whether your perception is real or not and again if you can't justify if y whether your perception is accurate or not in the moment then the skeptical problem reemerges you can't justify your perceptions so you can't justify your beliefs and so the skeptic would insist that you can't have knowledge a different approach to defending our ordinary knowledge against the skeptical challenge instead focuses on the definition of knowledge so all the other responses the skepticism we've looked at so far assume that knowledge requires something like justification and this is where the Skeptics argument gains a foothold because uh if we can't justify whether we're in the real world or whether we're in some skeptical scenario such as the evil demon then we can't justify the accuracy of our perceptions and any beliefs that result from them if we can't justify the accuracy of our perceptions because those perceptions are equally consistent with skeptical scenarios where those same beliefs are false then we can't justify our beliefs and so we can't possess knowledge if knowledge requires justification but perhaps this kind of justification is not necessary for knowledge if you remember reliabl ISM from the definitions of knowledge video this definition rejects the justification condition of knowledge and instead replaces it with something like formed via a reliable process so a reliable method is one that produces true beliefs consistently and in a reliable fashion and the difference between a reliable method and a justification is that where a justification requires you to be able to explain the process or provide kind of underlying reasons that support the belief a reliable method doesn't require this so for example a dog can't justify its belief that there is food in the bowl and yet it knows there is food in the bowl because this belief was formed via its eyesight let's say and let's say it eyesight is accurate and reliable or if a person can reliably tell two sets of twins apart even if they can't justify or explain how they know which twin is which then their belief about which twin is which does count as knowledge even though it isn't properly Justified anyway a to the skeptical challenge reliabilism can argue that most ordinary knowledge is formed by a reliable method assuming I'm not in one of these skeptical scenarios like the evil demon or brain in a VAP then my eyesight and other methods of forming beliefs do count as reliable methods because they cause me to form true beliefs assuming I'm not a brain of that then when I look at this elephant my eyesight causes me to form the belief that this is an elephant and because I'm not a brain in of that my belief is true now of course I can't justify my belief that I'm not a brain in vat but I don't have to justify my belief for my belief that this is an elephant to count as knowledge because the belief is true regardless of whether I can prove it and it's formed bya a reliable method I.E my eyesight of course I still can't know I'm not in one of these skeptical scenarios my eyesight can't distinguish between the brain in of that scenario and the real world scenarios but that doesn't matter assuming I'm not in one of these skeptical scenarios regardless of whether I can prove it or not then I'm forming true beliefs in a reliable method using my eyesight and so my belief that I have hands counts as knowledge because it's a true belief formed by a reliable method obviously if I am in the brain in that scenario or the evil demon scenario then my belief that I have hands doesn't count as knowledge because my belief is false and my eyesight is unreliable so I can't know that I know I have hands according to reliabl ISM but you don't need to know that you know something in order to know something if that makes sense basically reliabilism defense of ordinary knowledge is conditional we can't know whether we're in the evil demon scenario or any of these other skeptical scenarios versus the real world scenario but if we are in the real world scenario then our ordinary beliefs are true and so our perceptions count as reliable methods and as such I can know that I have hands because it's a true belief formed via a reliable method however for this response to succeed then reliabilism needs to be the correct definition of knowledge but as we saw in the definitions of knowledge video getia cases are a potential issue for the definition of knowledge as true belief formed via a reliable method so I don't want to uh reopen this whole can of worms but just as a quick reminder of get yet cases let's say you have perfect hearing and so your hearing counts as a reliable method you hear the noise your phone makes when you get a message and form the belief that I have a message so you pick up your phone and you do indeed have a message and so your belief was true but it turns out your phone was actually on silent and by pure coincidence someone else's phone that has the same ringtone went off at the exact same time that you got the message so here your belief that I have a message was formed bya a reliable method I.E your hearing and it turned out to be true you did indeed have a message and so although although it's a true belief formed via a reliable method we perhaps don't want to say that this counted as knowledge because it was just lucky that you really did get a message at the same time the other person's phone went off if you didn't happen to get a message at that exact moment you'd have formed the exact same belief but your belief would have been false and so it seems a bit of a stretch to say your belief here counted as knowledge despite being a true belief formed by a reliable method so what this example is supposed to show is that reliabilism or at least true belief formed by a reliable process is not sufficient for knowledge and so it isn't the correct definition of knowledge and if this isn't the correct definition of knowledge then we can't use it to defend our ordinary knowledge claims such as I know I have hands against the Skeptics challenge even if it's true that I have hands and so my belief that I have hands is true and foral via a reliable method this doesn't prove that I know I have hands because uh true belief formed bya a reliable method is not sufficient for knowledge and so if this isn't the correct definition of knowledge then we can't use it to defend our ordinary knowledge claims against the skeptic's challenge so to summarize this skepticism topic we have these scenarios that create philosophical doubt such as the evil demon the simulation hypothesis brain VAP The Matrix and so on and the point of these scenarios is they are scenarios where all your beliefs could be false and you wouldn't be able to tell the difference so because of this philosophical doubt the global skeptic argues that we can't possess any knowledge whatsoever and just to reiterate the skeptic doesn't claim that we really are in these skeptical scenarios that we really are a brain in a vat or being deceived by an evil demon or whatever instead the Skeptics claim is that because we can't tell the difference between uh these skeptical scenarios and the real world scenario where our beliefs are true then we can't justify our beliefs and so that's why we can't possess knowledge so to respond to skepticism we don't necessarily have to prove that we're not in one of these skeptical scenarios we don't have to prove we are not a brain inov that or that we're not being deceived by an evil Dem although that would be nice instead all the non-septic has to do is to defend their ordinary knowledge claims as knowledge despite the possibility of these skeptical scenarios so we saw several ways we might defend ordinary knowledge claims such as I know I have hands against the Skeptics challenge we saw how dayart rejects skepticism headon by arguing that God exists and so God wouldn't deceive him or allow him to be deceived about the existence of his hands next we saw how Russell might potentially argue that while we can't be 100% certain that we have hands the existence of our hands is the best explanation of our perception of our hands and so as the best hypothesis my belief that I have hands can be justified then we saw how the skeptic's argument never really gets going against idealism as according to this theory of perception to be is to be perceived and so if you perceive that you have hands then it must be true that you have hands and finally we saw how reliabl ISM an externalist definition of knowledge sidesteps this skeptic's argument altogether by arguing that my belief that I have hands doesn't require justification to count as knowledge philosophical skepticism is really the quential philosophy debate or at least the quential epistemology debate it goes back even earlier than dayart and his evil demon in the 1600s back to Plato and his cave in the 4th Century BC and even earlier than that um everyone you over the years from you know teenage stoners to these philosophical heavyweights has been considering a version of these skeptical scenarios and um the debate is still very much a live one today with far more to it than I've covered here today day but of course this whole debate is one that has zero impact on our lives but uh still fun to talk about and uh I hope you found this video interesting so that about does it for philosophical skepticism and with it the epistemology topic so uh over the course of the next few videos we're going to move on to something much more practical which is uh moral philosophy so uh All That Remains for this video is the part where everyone clicks off but it's actually my favorite part which is the bit where I uh review the books but unfortunately uh we didn't cover many books today so if you did want to research this topic in a bit more detail um I'll link some useful links below um anyway books um as always you can get my book um don't think there's that much more than what we talked about today and it's also on my website so if you're getting my book for skepticism maybe just get the website but um I probably seem like a marketing agent for copies of day cart's meditations at this point but I really do recommend this book it's uh like I said in every video it's it's great so uh yeah get yourself a copy of day carts meditations and if you well whatever [Music] right going really mad this time um I think that about does it for this video thank you so much as always for watching and uh yeah we will see you in the next one [Music]