Part Three, Do We Have any Knowledge? In this part, we're going to be looking at the problem of Radical Scepticism. Now this is the problem of demonstrating that we have as much knowledge as we take ourselves to have. In particular, there is this challenge, it's called the Sceptical Challenge, which says that we don't know very much, and in fact, in its strongest form, radical scepticism says that knowledge is impossible. So, we think we know lots of things, but in fact, actually we know next to nothing, perhaps even nothing. Now, there's a very influential form of radical scepticism, which goes back at least to Descartes, on certain views it goes back right even to the ancients, which makes appeal to sceptical hypotheses. So these are scenarios that are completely indistinguishable from normal life but where one is radically deceived and what the radical sceptic does is say, well, you can't know that these sceptical hypotheses don't obtain. And so far as you don't know that they obtain, you can't possibly know anything, or at least you can't know anything about a world that's external to you, anyway. So a good way of thinking through what's going on here is to take a particular kind of skeptical argument, and unpack it. So what we'll do is we'll look at a specific sort of skeptical hypothesis, which is known as the Brain-in-a-Vat Hypothesis. So, this is the idea that, although we think right now that we're causing and interacting with others in the context of a shared world, that we're embodied people that, perhaps we're not, perhaps our brains have been harvested, they've been taken outside of our bodies and they're floating somewhere in a vat of nutrients being fed fake experiences. This is the Brain-in-a-Vat sceptical Hypothesis. If you've seen the movie The Matrix, by the way, this is roughly the kind of scenario that's depicted there. Here is the question. Do we know that we're not brains in vats? Do we know we're not the victim of this skeptical hypothesis? Now on the face of it seems, how would we know? How could we possibly know that we're not the victim to such a scenario? I mean, think of the evidence that you might cite for thinking that you're not the victim of such a scenario. So you might say, well, look, I can see my hands, I can feel my body, I can reach out and touch things but of course, if you were brain-in-a-vat being fed fake experiences, then everything would feel the same way. I mean, you would seem to see hands, you would seem to touch things when you move your hands around in your fake environment and so on. The problem is that these scenarios seem to be constructed in such a way that it's just impossible to rule them out, impossible to know their faults. So I can't that I'm not a brain in a vat. And in general I can't know that the denials of skeptical hypotheses. They're constructed in such a way that there's nothing that I could bring to bare which could exclude them. All the evidence that I might cite against them is the sort of evidence which is called into question by the scenario itself. So I can't know that I'm not a brain in a vat. What follows in terms of my everyday knowledge? I mean, one might think, well, so what? There are far-fetched scenarios and one can't know that they're false, what difference does that make? But here's the problem, in so far I can't know what the brain-in-a-vat, well, how then can I know for example that I've got two hands right now? Think for example the basis that I have for thinking that I’ve got two hands, which presumably I can feel my hands, I can see my hands and so on. Of course the problem is that the brain-in-a-vat can see and feel hands too even they don’t have hands. Having hands is inconsistent with being a brain-in-a-vat. So how then can it be that I can know that I’ve got hands and yet not know whether or not I'm a brain in a vat? And of course, what the skeptic is doing here is they're saying, well look, if you really can't rule out the scenario that you're brain in a vat, well, then how can you possibly know something so mundane as that you've got hands? You'd only have hands if you weren't a brain in a vat. You don't know that you're not a brain in a vat. So we can see there's an argument starting to appear here. Two premises in a conclusion. The first premise is just, you can't know you're not a brain-in-a-vat. The second premise, like the bridging premise says, if you don't know you're not a brain-in-a-vat, then you don't know very much. You don't know, for example, if you've got hands, you don't know your stomach, and basically you don't know all the things that you take yourself to know, which are inconsistent with being a brain-in-a-vat. And hence, well, you don't know very much. You think you know you've got hands. You think you know, in my case, I think I know I'm standing here right now talking to you. But of course if I was a brain-in-a-vat, it would seem to me as if I was standing here talking to you as well. And I can't exclude that, so how can I possibly know that I'm standing here talking to you right now? One thing to note about this is that the skeptic is not saying that you are a brain-in-a-vat or even that it's likely you're a brain-in-a-vat or anything like that. So it's perfectly consistent with this skeptical argument that brains-in-vats are really far fetched and really quite science fictiony style scenarios. All that matters Is that you don't know that they're false. It doesn't matter whether or not they're likely, or some, the skeptic doesnt' making any claim of that sort, they're just simply saying you don't know that they're false. And their arguing, well look, if you don't know they're false, how can you possibly know all the things that you take yourself to know about your environment? Things that wouldn't be true if you were a brain-in-a-vat. So we've confronted this skeptical argument which purports to show that we can't know very much, that we can't know much about a world that's external to ourselves. It's not obvious how to deal with such as a skeptical problem. For example, what option might we just say that we do know [INAUDIBLE] of skeptical hypotheses? But that’s a difficult claim to make stick. In virtue of what, if we do know we're not brains in vast for example, in virtue of what do we know such a thing? It can’t be in virtue of perceptual evidence, the things that I’m seeing and feeling right now because of course the brain in a vat would see and feel these things and so. It seems whatever kind of evidence that we cite would be compatible with the skeptical scenario by definition. So, it's hard to say how we could know the skeptical scenario is false. But once we've conceded that we can't know the denials of skeptical hypotheses, it's hard to resist the skeptical conclusion now. It can't be both true that I'm a brain-in-a-vat and that I've got two hands, so if I do know that I've got two hands, then what it seems, I must be able to know that I'm not a Brain-of-a-Vat, right? Because Brains-in-vats don't have hands. So conversely, if I can't know that I'm not a Brain-of-a-Vat, how can I know something so basic as that I've got two hands? One way in which one might be tempted to respond to this skeptical problem, is to say that there must be some sort of trick going on here. That maybe there's a kind of a raising of the standards. Or maybe the skeptic is saying, well, to a very high standard for knowledge we don't know, the kind of standard for knowledge that requires us to rule out the possibility of brains-in-vats and so forth, relative to that standard we don't have knowledge, but relative to a less demanding standard, we do know. I think it ought to be clear on closer inspection that isn't going to work. The skeptic isn't appealing to high standards here for knowledge in order to motivate their skepticism. If the skeptical argument goes through, then it goes through any standard for knowledge. So think right now of my belief that I've got two hands. If the skeptic is right, they're not saying that you've got some reason for believing what you do. It's just it's not very good, It's not good enough for knowing by their exacting standard. What they're saying is you have no reason at all for believing you've got two hands because all the reasons that you might plausibly offer are all reasons that presuppose that you're not a brain-in-a-vat. And you can't rule out the possibility that you're a brain-in-a-vat. So if the skeptical argument goes through, it works at high demanding standards for knowledge and it works at low undemanding standards for knowledge too. This means the skeptical problem isn't amenable to a simple solution. Now there are various ways that people have offered for dealing with skepticism, but one possibility of course is that the skeptic is onto something. Maybe it's true that when we start to reflect on the nature of our epistemic position in a very general way, once we start to step outside of our normal life where we're not thinking about skeptical scenarios, and we're just offering reasons and thinking through the beliefs that we have in a very localized way. Once we step outside those normal confines, and start to reflect in a very general way about the nature of our epistemic position, perhaps what we discover is that we don't have such a grip on the truth, on reality as we thought we did. We might think of this as kind of an epistemic vertigo. That as one starts to step back from our normal everyday lives and starts to reflect on one's epistemic position, one starts to sort of as it were reflectively ascend and start to think about one's beliefs as a whole and what their connection is to reality, we may well discover that perhaps we don't know as much as we thought we do. We might even just go with, we don't know anything. Okay, Part Three, Conclusions. Radical Scepticism is the view that we know very little. In particular, we know very little, if anything, about a world that's external to us. We know too, that radical scepticism makes you sort of sceptical at hypotheses. So these are scenarios which are indistinguishable from normal life, but where one is radically in error. So one of these scenarios that we looked at was a Brain-in-a-Vat Hypothesis. This is the scenario that one is not causally interacting with an environment in the usual sort of way that one thinks one is, but rather one's brain has been taken out of one's head and is floating somewhere in a vat of nutrients being fed fake experiences. We noted that, because skeptical hypotheses are indistinguishable from normal life, that it seems there's no way for us to know that they're false. No way that we could rule them out. And from that conclusion, the skeptic seems able to motivate the thought that, well, we don't know anything then very much about the world around us. In particular, given that if I have got two hands, well, I must not be a brain in a vat, because brains in vats don't have hands. It seems if I can't know that I'm not a brain in a vat, I can't know that I've got two hands. And if I don't know that, then what is it that I do know? That's the problem with radical skepticism. If you're interested in learning more about the theory of knowledge, then you may find it helpful to take a look at my introductory textbook, which is called What is This Thing Called Knowledge, and it's published by Routledge. Thank you for listening.
