 OK, rhaid i ddweud, mae'n cymhwyl i gael beth, bydda'n gwneud yn ysgolol, a rhaid i gael beth o'n gwneud yn ysgol—y nesaf, ddim yn ddweud. OK, a rhaid i ddweud yn ysgolol. Dw i'n meddwl i ni, efo fi rhywbeth yny o'r mwyaf ymlaen uch yn y coulwb hon i gyll wideriaeth cysylltiadau ymlaenol. Rwy'n gweithio ddau sy'n cyffredinol, mae'r argument ar hyn i gyllfnodau gyllweithau yn y pwylo sy'n gyfarfodd o gwelir. Roedd rwy'n patrwch gyllteisim hwn i mwyaf, is skepticism about other minds, and ask how Putnam's thing bears on that, and then finally look at what Putnam's proof that we're not all brains in a vat tells you about your knowledge of your own thoughts. They can't famously thought that your knowledge of your own thoughts is the most certain thing from which you begin in knowing about anything at all. And Putnam's proof seems to me kind of shapes that up a bit. But I want to begin with a couple of remarks. First about, I think anyone's first reaction to Putnam's proof is that this is some kind of ridiculous trick, and it can't possibly be right. But there is something, I should say, something resonant about it. There's some important thing that is right about this proof, which is if you think of classical responses to skepticism, well, skepticism says the world might be one way and your mind might come completely adrift from the world. They might not be in sync with your mind in the world. What your mind is thinking might be completely different to what's actually going on. And one classic answer to that is idealism, to say there is no more to the existence of the tables and the chairs. There is no more to the existence of other people even than me having sensations than me having ideas. That's all you all are, just a bunch of sensations in my head. Now if that was right, then skepticism would indeed be impossible, because skepticism says maybe your mind is coming adrift from the way the world is out there. Idealism kind of shrinks the world to the size of the mind, and that's how it gets the effect that the world can't come adrift from the mind. Putnam's picture is kind of the opposite of that. It's that the world can't come adrift from the mind, because according to a causal picture of how we have meaning and reference in the first place, the world actually invades the mind. The world shapes the mind in its own image. It's because the mind is not independent of the world. The mind has the representation it does only because the world shapes it, therefore the mind can't come adrift from the world. So if the mind is constituted by the way the physical world is, then you get that anti-sceptical thrust, and there's something very powerful about that background picture. On the other hand, so that's I think one reason, one background reason why Putnam's thing is very important, that there is a background picture there that has something right about it. It seems like a healthier response to scepticism than idealism. On the other hand, there is a feeling that Putnam's proof can't be right, that it must prove too much. I mean that it seems to me, people have been trying to find responses to the sceptic for thousands of years, right philosophers have thought for thousands of years about, if someone says to you, you might be a brain in a vat or you might be dreaming, how can you prove that they're wrong? But it seems to me that we don't actually want a proof that they're wrong. What I mean is, suppose you have a brain in a vat, suppose there it is, it's all wired up, as you can see what it's thinking, suppose that we have it on a TV screen what the brain is thinking. And you can see that now it thinks it's riding a horseback, now it thinks it's singing in an opera, now it thinks it's puzzled by abstract philosophical puzzles. And if the brain gets, you can see that let's suppose that the brain is getting gripped by an abstract philosophical puzzle, it thinks maybe I'm a brain in a vat. But then you just feed it in Putnam's proof that it can't be a brain in a vat and it thinks, oh thank God, until I read Putnam's proof I was really troubled by the thought that I might be a brain in a vat. But now I can see clearly that I'm not. I mean if you have a really good proof that scepticism is wrong, then it's going to be a proof that the brain in the vat could use. But if the brain in the vat can prove that it's not a brain in a vat, well it's hard to feel that something must have gone wrong if you see what I mean. So although Putnam's proof seems very, I think it does seem very plausible and powerful, we don't want a response to scepticism that's too good. There's a sense in which we want to be troubled by scepticism because if we had a really good satisfactory resolution, the brain in the vat could use it. You see what I mean? So these are just two background initial thoughts. So Let me just work over Putnam's proof. So the sceptic says are the causes of my experiences as I take them to be, as we said last time, the standard sceptical scenarios are ones in which your experiences have causes but they're non standard causes. Your sensations are figments of the hetoprised brain that are produced by evil demons or madness or an evil scientist or a vat and vat-tending machinery, something like that. Something not the regular tables and chairs and the other people is generating all these experiences in you. And the response to that is that well just as on earth and on twin earth we interpret your mental pictures, we interpret your talk about water so that it comes out roughly right about the stuff in your environment. If you're on earth then we say this, when you talk about water, when you have this kind of mental image that refers to H2O because that's the stuff in your environment, that's the stuff that's causing this. On twin earth we say well when people there talk about water they have those kind of images, that's about XYZ because that's the stuff there that's causally generating those images and thoughts. Well if you're in a vat then you're having those same images, you're using the word water and so on but by just the same logic, by just the same argument you are to be interpreted as talking about the stuff in your environment which will be aspects of the vat-tending machinery. So there is going to be a question as to okay it works for water and remember we said last time we had these discussions about whether it works for kettle or, I can't remember what the other examples were, airplane. If we didn't talk about it, it was gone, it's completely gone. Maybe we could run this kind of argument for most of our vocabulary. Presumably it's not going to work for words for sensations. Words for sensations are standing for the sensations that, how should I say they're inside your head? So there's no possibility of lookalikes or something different in the environment being the referent, you can't have two in our cases there. But if we just set the sensations aside for a moment, well certainly the word vat itself, if you're in the vat then what is the word vat stand for? Well it stands for whatever is causally connected to the use of the word vat. That is not the name of a sensation so presumably it will be subject to Putnam's argument. So if we consider the brain of the vat, the use of vat in vat English has no causal connection to real vats and here comes Putnam with a tricky bit in the argument. You might say of course it does have a causal connection to vats because after all the brain is in a vat and it couldn't think anything at all, it couldn't say it wouldn't be alive if it wasn't for the vats. It does this causally connected to the vat so the use of the vat in vat English has no causal connection to real vats apart from the connection that the brains in a vat wouldn't be able to use the word vat if it were not for the presence of one particular vat the vat they are in. This isn't going too fast. But that connection obtains between the use of every word in vat English and that one particular vat. So we had these discussions about what's the right kind of causal connection. Remember that you're talking about the computer, the sun may be all that's letting you see the computer but you're not thereby referring to the sun. The vat may be part of the background that makes it possible for you to refer to particular things but it's not thereby what you're talking about. So the word vat in vat English has no relevant causal connection to real vats. So if you are a brain in a vat and you utter the words I am a brain in a vat then when you use them they say something different to what they say in regular English assuming they're in regular English but not actually in a vat. Is this getting too technical? Okay. And so if you are a brain in a vat then when you say I'm a brain in a vat that will be saying something false because what you'd be saying is you'd be talking about some configuration of the vat tending machinery. You're talking about a vat and you aren't actually a configuration of the vat tending machinery. You're a brain, yes? So that would be false if you say I'm a brain in a vat. A brain wouldn't refer to brains either. A brain would refer to some configuration of the vat tending machinery. You'd be saying that you are a particular configuration of the vat tending machinery which is wrong. Is that all right? So there are two scenarios. One is the word is just the way you think it is. Here you are in this agreeable lecture room with all your colleagues and there's not a vat in sight so if you're in that situation and you say I'm a brain in a vat you say something false. Yes? But it's also true that if you are a brain in a vat and you say the words I'm a brain in a vat then you also say something false. Yep. So you can't be a brain in a vat. I mean you can't say something true by saying I'm a brain in a vat. Yes? Because well you can't say something true by saying I'm a brain in a vat if you're a brain in a vat. Because if you're a brain in a vat the words I'm a brain in a vat well brain is going to stand for a configuration of the vat tending machinery. Vat is going to stand for a configuration of the vat tending machinery. So when you say the words I'm a brain in a vat you're saying something false because you're not a configuration of the vat tending machinery. Even in that situation you're a brain. So if you try it now saying I am a brain in a vat you know that one thing you know is that that's false. Well there you go. What more do you want? Bingo. So you know you're not a brain in a vat and how should I say? Even if you are a brain in a vat most of the sentence that you're using e.g. there are birds in the trees they're going to come out mostly true. Because they're all statements about configurations of the vat tending machinery and they'll mostly be right. So most of the things you would regularly say come out true. Yes right. I am anything. That's very interesting. I am tall. What would tall be? I am tall. It tells a little bit different. I am a brain in a vat is an identity statement. That would be one of these informative identities that we hear so much about. But I am tall is not an identity statement. I am tall just say something like I am in a particular vat configuration. That is very interesting. I think that's right. The thing is I said maybe it's only words for sensations that don't work with the causal theory. But I is interesting here and here is interesting. Because I and here maybe are words that don't function in accordance with the causal theory. What I mean is with words like I and here with I you've got a rule anytime someone uses I it refers to that person. It's something like that. So there's this absolutely rigorous rule and it doesn't really matter who is causing anything. It's not really a causal motion. Here anytime someone uses here it refers to the place that person is at. Then there's this absolutely rigorous general rule fixing the reference of the term. Not something about what's causing the use of the term. That's right. That's right. That's right. That's right. That's right. That's right. That's right. That's right. That's very good. Could you have a twin earth for existence? That's the basic question. Could you have a twin earth for uses of I? That's the way to frame what both of these things are raising. It seems to me that you couldn't for either of them have a twin earth. This is actually agreeing with your point. I think that's what makes your point possible. These signs are getting meaning in a way that doesn't depend on a causal theory of reference. I just agree with that. It would be false. I'm inclined to think it would be true that I exist. Even if the brain of that says it when it says I exist, that would be something true. That's right. That's correct. I think in general that's right. I do wonder though what I mean about existence is I wonder if that isn't an exception. I don't think that helps Putnam. I think you could present it as a dilemma. Either he says you could have a twin earth for existence. In which case he goes down your crack. Maybe it's going to come out that existence refers to a particular kind of vibration in the vat tending machinery. Then when it says I exist, maybe it itself is not actually correlated with that kind of vibration in the vat tending machinery. That would be the kind of point. On the other hand, I think you could go down the other crack, which is what I was suggesting, and say that seems daft because we don't actually think of existence, the notion of existence as governed by a causal theory. Then you see it's got to be true when the brain says I exist. If anyone in any context can say I exist, that's got to be right. But the causal theory can't make sense of that. That's very interesting. I just hadn't thought of existence in this context. I think that's right. There's someone over here. You're me talking about actual events. That would be too strong. You're right, that would be the wrong answer if you came to the conclusion. We can't talk about what was going on in the Middle Ages because we never directly experienced any of these people. That can't be right. The important notion here is not directly experienced but caused. People in the Middle Ages are causally connected to you or me. We are picking up on causal chains that go back to these people, so we think anyhow. Whereas the brain in the vat, let us suppose at any rate it was born in the vat. It was grown in the vat. It's not causally connected to any of the regular stuff. That's what we really want. If you're not a little bit confused, you haven't really understood what's happening. Are you a little bit confused? These are questions about I and existence. I really want to pick up on that thinking particularly about sensations. It seems to me, as I said, with I here now, it's not really a general causal theory of reference functioning. It's these systemic rules governing the use of the terms. If you say now, maybe there are time delays in your perception. Maybe you're in an environment where there are time lags. It takes 30 minutes for the light to get from the chair over here. That could happen. You could just be in an environment where things go very slowly like that. But then when you say now, you might usually be talking about stuff that happened. That might be causally connected to stuff that was happening 30 minutes ago, if you see what I mean. But that would be an illusion. You'd still be making a mistake. Because now always refers to the time at which you're speaking. So there's just a general iron rule here for these terms. What you're causally connected to is not so important. Or names for sensations. My picture here is pretty crude, but my intuitive picture here is, this is your mind. This is the world with all the trees and the vat-tending machinery and the H2O and the XYZ. All that stuff is causing things to happen in your mind. But your sensations, your headache, they're right in there. They're too close to be causally connected to you. If you see what I mean. You're surveying them in their entirety. It's not just that you're causally connected to them. So, when you think about what it is, what's going on when you use a word like pain? Well, it seems like if I say, are you hurting? Is your head sore? Then what I'm asking there is not a question about whatever property is at the end of some causal chain. I know from my own case what pain is. You know from your own case what pain is. If you ask someone else, do they have a headache? You're asking whether they have that sensation that you have had so often. So, what's going on when people are skeptical about other minds, as they say? Maybe I'm the only sentient one. Maybe you guys are all just very clever zombies and you don't have sensations at all. Or maybe something is going on but it's completely unlike what is going on in my mind. How could we ever know? I mean people very often feel that second kind of skepticism anyway. But you don't really know at all what's going on in someone else's mind. There's something alien about practically everybody else. So, when you raise that kind of question about other minds, if you ask about other people, are their sensations the same as mine? Or do they have experiences at all? Well, a platinum at some point seems to think that he's addressing that kind of skepticism too. Because the picture is, well, maybe here we all are, brains bobbing together in one giant vat. Maybe all the people that they've ever lived are just all bobbing about. Like apples in a bucket in the same big vat. But of course, that's not the right picture at all. Because if we're all brains in a vat, then there's no communication between you and me, if you see no direct communication. We're always being fed by the vat, by the vat tending machinery. So, if you really took Putnam's picture there seriously, all you'd be saying is, when I say pain, I'm referring to whatever out there usually causes me to use the word pain. But what's out there that usually causes me to use the word pain if what I'm talking about other people's pain is going to be some configuration of the vat tending machinery. There's something in the vat tending machinery, some configuration of the chips in the vat tending machinery that send me a jolt that make me say, oh, you've got a terrible headache. Oh, you've hurt your arm. You see what I mean? But that's not how it works with pain. We know what pain is well enough from our own case. Putnam's picture is that Neo, if we can call our brain Neo, when Neo talks about pain, then Neo's talking about states of the machinery or maybe even states of other brains in there. So if you suppose that someone else is having a particular sensation, then when I say other people have headaches, I'm not just talking about whatever it is that usually causes me to use those terms. I'm supposing that they have the same as I do. You know what the sensations and feelings are independently of any causal connections. So when I suppose that you're having a headache or a feeling of bliss, then I know what I'm talking about and it doesn't depend on what I'm causally connected to. So if I'm in the vat and I'm supposing that someone else is in a particular conscious state, that can't be right to interpret that as merely my supposing that some part of the machinery is in a particular machine state. You see what I mean? When Neo in the vat is supposing that these things around him all have feelings and sensations, that they all have conscious lives, that's not just a matter of getting particular synchronised firing in the vat-ending machinery. So when you suppose someone else to be in a particular conscious state, you might be referring to something in the vat, but you're supposing that it's conscious in the same way you are. You know from your own case what consciousness is and you're supposing that something else has that. So it seems to me Putnam's proof doesn't help a bit with scepticism about other minds. I mean if you are in the vat and you formulate the thought maybe I'm the only conscious thing in the universe, then you are correct in that hypothesis. It's not as if it gets formulated so as to reinterpret it so as to come out true. So if you have these sceptical doubts, maybe no one else has feelings, maybe no one else has feelings the way I do. If you're a brain in the vat, all those doubts are correct, even in Putnam's theory, because Putnam's theory can't apply towards like I, towards those sensations. Here ends the first lesson. I realise it's a bit early for this kind of scenario. I think it doesn't really matter. Whether you're the only one or not, I mean I think when Putnam does that thing of supposing that the brains are all bobbing about there, it doesn't really affect the fundamental point that they're isolated from each other. They're all being dealt with by, they're all being stimulated by the vat-tending machinery. So if the regular causes of your uses of words are what's going on in the vat-tending machinery, and when I say, when I have this doubt, maybe I'm the only one in the room that actually is conscious, maybe everybody else is just moving and acting as though they're conscious. That is the sceptical thought. There's evidence that they're conscious, but it's not conclusive, it might be misleading. Then the mere fact that there are other brains around who happen to be occupying the same vat is going to, I mean I'm not referring to any of them, because I'm not causally wired up to any of them. So when I have that doubt, maybe I'm the only conscious one, that's going to be true if I'm a brain in the vat. That's right. Nothing in the vat-tending machinery is conscious. So it's all right for Putnam to say, when I talk about trees, there are birds singing in the trees. That's just talking about configurations of the vat-tending machinery. I actually agree you can do that kind of reinterpretation there, but in the case of terms like conscious or feels pain, since I know from my own case exactly what I'm talking about here, and I'm supposing that that thing, whatever's going on in here, is also going on out there, then I get to keep hold of the meanings of my signs, and it comes out meaning something false. That's right. No, wait a minute. I'm taking you for granted that I'm conscious. That's the whole thing about the brain in the vat. It's conscious all right. That's what... To take me through this again, I'm sorry. It's a bit early for me too. I see. That's perfectly fair. I slid over something there. The way I meant to keep putting it was to say, I'm the only one in the room that is conscious. Yeah. Now, if you can say something much more general, like I'm the only one in the universe that's conscious, then maybe that will come out false because there are either brains and maybe they are all conscious too. But what I meant about... When you actually do feel sceptical about other minds, what you mean is, of all the people you know, you're the only one that's conscious. That will be the thing that's coming out true for the brain in the vat because it doesn't know anything about these other brains. All you guys will just be states of the vat-tending machinery. I'm sorry to say. You see what I mean? You can do this too. I'll be over when they get to do this. Perfectly clear. The point there is that there's something... You can hive off scepticism about other minds and say Putnam's proof, even however good it is, it just doesn't seem to work for scepticism about other minds. It doesn't help scepticism about other minds because the key terms don't seem to be subject to a causal theory of reference. You don't have to agree with that, but it's very important that you see what the idea is anyhow. I've been saying so far that scepticism is... You can always put scepticism as a question about what the causes of your experiences are, but it's not obvious that it's really essential to scepticism. It's very natural when you're trying to explain to someone what scepticism is to say, well, maybe it's all a dream or maybe it's just states of the vat-tending machinery or something like that. That helps people get how scepticism might be true. But suppose the sceptic said, forget all the stuff about vats, forget all the stuff about evil geniuses and dreaming and demons and so on. That's all the stage setting. The really critical puzzle is suppose that all is going on right as you sit here is that you are having a procession of sensory images and maybe there is nothing more to the universe than that procession of sensory images. So maybe they have no causes at all. Maybe that's all that is going on. There isn't any causation. Suppose the sceptic says that. That seems like just another form of scepticism. So all that there is constituting the entire universe is that procession of images in the void. That's the whole thing. So that's scepticism all right. So what does Putnam say to that? Well, what would be the right Putnam reaction to that? All is going on. The whole universe, as you sit there, you're getting one sensory impression after another and that's the whole thing. No causes. Well, if you have a causal theory of reference and thought then if there are no causes then you don't have those causal contextual connections that are needed for you to be thinking about anything. If we consider the hypothesis that there are only images and the void then the right conclusion is that you're not thinking. You're just having a bunch of sensory impressions. Descartes thought that when you get to the existence of your own thoughts that's the fundamental certainty from which or which all the rest of knowledge depends. But what Putnam has shown is really, it's not that he's helped against the sceptic. He's actually just made things worse because Descartes thought, well maybe it's all a dream, maybe it's all illusion but still in all I have my thoughts and I know about my own thinking and that much is certain. And the causal theory of reference hasn't helped at all because now the sceptic can reformulate in such a way where if the sceptic puts scepticism as a hypothesis that there are only images and the void then the sceptic can attack even the idea that you know about your own thoughts. So Putnam hasn't helped. Look, there's a kind of a scary story due to Donald Davidson that gives another way of putting this point. Suppose this scene, suppose it's midnight out on the outskirts of town and suddenly a bolt of lightning hits a swamp and by some peculiar chemical biological reactions I don't really have the vocabulary to explain to you exactly what happens but as a lightning hits the swamp some strange set of reactions come in place and out from the ooze there clumbers a figure which is first of all you realise it's alive and then you realise it looks exactly like you. It's not just like you, it's molecule for molecule identical to you. So it clumbers out, dusts itself off. What is Swampman thinking about? Suppose you were thinking about those happy days when you were five years old and you were sick at your birthday party. Swampman's going to have those kind of images going through their head but are they thinking about the same event, the same people? No, of course not. Why not? Because what do we need to be thinking about particular people from the past class? Causal connections. Does Swampman have causal connections to any of these people? No, Swampman didn't exist two minutes ago. Swampman just got generated by the bolt of lightning. So Swampman isn't thinking about anything and a causal theory of reference. I mean all they can be thinking about is the swamp. So even though they're molecule for molecule identical to you they're not thinking about anything at all. And now suppose that what we do is, that was Davison's idea, a bolt of lightning hits the swamp and then what comes out might have some sessions but it doesn't have thoughts. It's not the way you do. But now suppose that what happens is that as you come into the class we show you the video. We say look, this is what happened last night. A bolt of lightning hit the swamp. You've only just cleaned all that stuff off you. You were only generated from the swamp last night. Everything before that in your apparent memories is actually just an illusion. Is that a contradiction? That could happen. We could prove to you that you weren't causally connected to any of those things. So the only thing you could do in that situation would be to conclude that you're not thinking. If we showed you the video. So you could actually have it proved to you that you're not thinking. So this is what I mean about the scepticism has only got worse. We started out with the idea that you might be doubtful about the concrete objects around you but your own mind you know about that all right. But the connection that the causal theory makes between the world around you and the constitution of your mind that's not helping against scepticism. It just means that the reach of scepticism goes further than you might have thought. If the whole world goes then your mind goes too. If the whole physical world goes then you can't be thinking. Yeah, it's a very paradoxical situation. All I can suggest is that you could go through the motions of thinking that you're not thinking. You could use all the right words but it would in a sense be just empty talk because none of these signs would really mean anything. On the other hand if you say this is not possible if I think I'm thinking then I'm thinking or if I'm going through the motions of thinking then I am thinking. So as you say that it doesn't matter what's going on around me then that's just to deny the causal theory because that's to treat your mind as if it's insulated from your environment and you know all about what's going on in here. But that's what happens with the causal theory. It blows that up. Since you can't know just by reflection that you have these causal or contextual connections to your world then you can't know just by reflection that you're thinking. So something really powerful happens when you have a causal theory of reference to the Cartesian picture of the mind to Descartes picture of the mind which is the natural picture of the mind. There are many people I think have this that I know what's going on in here other people maybe don't and certainly I know what's going on in here if whatever is going on out there. That's a very natural picture to have but the causal theory is just blowing that up. So what Putnam wanted the causal theory of reference to show was that you know all the things you think you know. But what I'm suggesting is it's not really that much help. All it does is it explains to you how it could be happening that all seems to you as though you're thinking you're not really thinking because you could have that kind of swamp man scenario. I mean you keep hoping we're going to make progress but there you go. Notice incidentally how this goes back to that basic point that we were looking at with Russell and Frager and so on about meaning without reference that the causal theory is saying you can't have meaning without reference and that's really what's at the heart of this the points here. On the Cartesian picture you can have meaning without reference so you can hold on to the meaning whatever's going on out there for you to refer to. I just want to make one last brief comment about even if you suppose that you are having thoughts if you have a causal theory of reference do you know which thoughts you're having? I mean if you get there to an earth in the VAT scenarios then the idea is you can have the same picture in all of these scenarios. I mean the same picture in your head in all these scenarios but you'll be having different thoughts because this one will be a thought about H2O this will be a thought about XYZ and this will be a thought about VAT tending machinery. The thing is what you now realise is that just by reflecting on your own mind you don't know which of these thoughts you're having so even if you are thinking if you have a causal theory of reference you don't know what you're thinking you don't know which of these you're thinking so we have less knowledge of our own minds than we thought and you might say it's been quite a popular thing for philosophers to say whichever of these scenarios I'm in I can say that well I'm thinking about water so you do know what you're thinking about you're thinking about water and whichever environment you're in whichever of these three environments you're in when you say I'm thinking about water you're going to be right so you might say I do know what I'm thinking about and then if you're in this environment water gets hooked back to the H2O water gets hooked back to the XYZ gets hooked back to the electrical impulses and the VAT tending machinery so you say well I do know what I'm thinking about but the thing is that just shows that that way of how should I say calibrating that way of expressing which thought you're having isn't really sensitive to which thought you're having and in this context you can say I'm thinking about water in this context you can say I'm thinking about water in this context you can use the words I'm thinking about water it always comes out right but that just shows that that way of expressing what you're thinking about is actually insensitive to which particular thought it is that you're having and Wittgenstein once said I know how tall I am I'm this tall each of us could do that I'm good at heights I know the height of everyone in the room you're this tall and I always get it right and you say what a talent what a gift and there is a sense in which when I do that I am indicating a height there's no question about that but the thing is that that way of specifying heights isn't any good the very thing that guarantees I always get it right is also the way that I said it's not as if what you really want is some independent measure that you can match everyone up against then you know what, that would be a different thing if I could say 5ft 10, 5ft 11, 6ft 3, whatever if I've got some independent yardstick for measuring heights what this kind of scenario shows is that saying I'm thinking about water doesn't give me an independent measure of what it is that I'm thinking it's something that whatever environment I'm in it gives me a correct report of what the thought is but it doesn't actually give me an independent measure of what an independent way of calibrating which thought that is I'm having because it's insensitive to this distinction just because of these distinctions it's like putting the hand in the head it's just guaranteed to always get it right so I think there is a real sense in which in this picture you don't know what you're thinking even if you're having thoughts you don't know whether you're having thoughts in the first place but even if you are having thoughts you haven't got any insight into which thoughts you're having so this locking between the mind and the world that the causal theory gets I mean as I say I think there is something very important about Putnam's picture there but Putnam treats it as though well you know what you're thinking alright but once from that you can generate your knowledge of the world that's how the proof is working but it seems to me it's also possible to run this backwards and say since I don't have certain knowledge of what the world is it follows that I don't have the kind of certain knowledge of what's going on in my mind that we always assumed we did have and on that bombshell we'll wrap in that on Putnam next time thanks