Part Three, Do We Have Any Knowledge. In this part we're going to be looking at the problem of radical skepticism, 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 skeptical challenge, which says that we don't know very much. And in fact, in it's strongest form, skepticism, radical skepticism 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, on certain views it goes back right even to the Ancients. Which makes appeal to skeptical hypotheses. So these are scenarios that are completely indistinguishable from normal life, but where one is radically deceived. What the radical skeptic does is say, well, you can't know that these skeptical hypotheses don't obtain, and in so far you don't know that they obtain you can't possibly know anything. 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 know as the brain-in-a-vat hypothesis. So this is the idea. That although we think right now that we're closely interacting with others in the context of a shared world, 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 skeptical hypothesis. If you've seen the film 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 the, 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 victims of 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. You might say, well look, I can see my hands. I can feel my body, you know. I can reach out and touch things. Because, if you were a 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 moved your hands around in your fake environment and so on. So the problem is that these scenarios seem to be constructed in such a way that it's just impossible to rule them out, it's impossible to know their faults, so I can't know that I'm not a brain-in-a-vat. And in general I can't know the denials of skeptical hypothesis. They're constructed in such a way that there's nothing that I, I could bring to bear which could exclude them. All the evidence that I might site 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, well one might think, well so what? There, there are far fetched scenarios and one can't know that they're false. What difference does that make? But, here's the problem. And so far as I can't know that I'm not a brain-in-a-vat. Well, then how can I know, for example, that I've got two hands right now. I mean, think for example, of the, the basis 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 though 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 is, they're saying well look, if you can't, if you really can't rule out the scenario that you're a 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 and a conclusion. The first premise is just you can't know you're not a brain-in-a-vat. The second premise, like [UNKNOWN] 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, you've got hands, don't know your stomach can, 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, 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 you know, quite science fictiony styled 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 the skeptic isn't making any claim of that sort. They're just simply saying you don't know that they're false. And they'll argue, 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 the 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 a skeptical problem. For example, one option might be to say that we do know that ours is a skeptical hypothesis. But that's, that's a difficult claim to make stick. I mean how, in virtue of what, if we do know we're not brains in vats for example, in virtue of what do we know such a thing? It can't be in virtue of what perceptual evidence. The things that I'm seeing or feeling right now because of course the brain-in-a-vat would see and feel these things. And so on. 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 that skeptical scenario's false. But once we've conceded that we can't know the denial of skeptical hypothesis, it's hard to resist the skeptical conclusion then. I mean. 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. Well, it seems I must be able to know that I'm not a brain-in-a-vat, right? Because brains-in-vats don't have hands. So conversely, if I can't know that I'm not a brain-in-a-vat, how can I know something basic as that I've got two hands. One way in which one might be tempted to respond to the 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 the, 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 the 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 in order to be clear on a closer inspection that, that isn't going to work. The skeptic isn't appealing to high standards here for knowledge in order to motivate their skeptisim. 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 to believe in 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 that 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 you're not a brain-in-a-vat and you can't rule out the possibility of brain-in-a-vat. See if the skeptic, skeptical argument goes through, it works at high demanding standards for knowledge and it works at low undemanding standards of knowledge too. This means the skeptical problem isn't ammeniable 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 on to something. Maybe it's true that when we start to reflect on the, the nature of our epistemic position in a very general way, once we start to step outside of our normal life where we're, we're not thinking about skeptical scenarios and we're just offering reasons and thinking through, the, the beliefs that we have in a very localized way. Once we step outside that, the, 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 that we thought we did. We might think of this as a kind of epistemic vertigo. That is, one starts to step back from our normal, every day lives. And starts to reflect on one's epistemic position. One, 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. They might even discover we don't know anything. Okay. Part three conclusions. Radical skepticism is the view that we know very little. In particular we know very little, if anything, about a world that is external to us. We noted that radical skepticism makes use of skeptical 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 the brain-in-a-bat hypothesis which is the scenario that one is not, you know, causally interacting with a, 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, then 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 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 of 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.