 Wel, oedden nhw yw yn mynd i'n gwneud cyfrifonau夜ig. Cyfrifonau llwyddio mae'r hyn o ddim ymlaen i'w cyfrifonau llwysig yn y war. Yr llwysag Hygrifon? Beth mae'n rhai? Rhae, rhaeth gyda. Felly mae hyn yn ysgol gyda'r llwysig. Ond rydyn ni'n gweithio gwybod yn rhan o'r cyfnodol i Crippgiadau. Rydyn ni'n gweithio i'n rhan o'r rhan o rydym ni'n gweithio'n ei hunain i'r gwahanol, o'r cyfnodol a'r cyfnodol o'r cyfnodol. Rydyn ni'n rhan o'r cyfnodol yn ymwyllgor o ran o'r cyfnodol, ac yn hynny'n gwybod i'r unig adeiladau, Mae'n cael ei wneud yn maelio'r cyflawn o'r ddod o'r ddod y cyflawn i'r un genedlaeth i'r un hwn. Mae'n cael ei cyflawni o'r ddod. Mae'n cael ei ddataeth efallai ddim yn ydym ni'n eu hyfforddiadau. Rwy'n credu'n meddwl i'r rysol o'r gwaith cyflawn. Fy ydych chi'n clywed am y drafodaeth o'r barachau, y bariau sydd yn ddeithas, nid o'r gweithio'r gweithiad hefyd ar y gallu pethau. Mae hyn yn cymwyffio'r cyllideinwyr o'r gweithio'r cyllideinwyr oedden nhw. Mae hyn yn cymwyffio'r cyllideinwyr oedden nhw, yn y cyflwyff o'r cyllideinwyr o'r cyllideinwyr, But that's it. He is stuck, and if he's right, then that's not just his condition, it's your condition. We are all stuck, trapped, are able to think and talk ultimately only about our own sense data, and everything else we say and think has to be interpreted in terms of that. And at this point, Frege can say, well, this is exactly what I was saying to you. If you're not very careful, you will wind up in this situation. And that was the point about the telescope that Frege has this distinction between the object that is being referred to, the sense, which is like the image in the mirror in the telescope, and the retinal pattern on the individual observer. He said, the meaning has to be like the image in the glass in the telescope, which is objective, the same for everyone, is only if you have the meaning as objective that you can have communication. If you think of the meaning as something like the hit in the retina, then you make communication impossible. And for Russell, what happens? Well, here is an analogy. This might seem a little bit left field, but if you can bear with me through this, then I think it helps getting Russell's picture. Suppose you think about how it goes for arithmetic, talking about the numbers. We have lots of different ways of specifying numbers. You can have how many terms, you can have definite descriptions for numbers. So if you say the number of the planets, well, that's a definite description, the number of the planets, like the author of Waverly or King of France or whatever, the number of the planets, that's a definite description, right? The. And the number of moons in the solar system, is that a definite description? The number of moons in the solar system. Yes. Yes, you can tell by the V, right? Okay, and this makes perfect sense. The number of the planets plus the number of moons in the solar system is a prime number. That makes perfect sense too. I don't have no idea if it's true, but it makes perfect sense, right? Or you can say every even number is the sum of two primes. Now if Russell's line is right, when you take this, the number of the planets plus the number of moons in the solar system, have you at any point named a number? No, because this is not the phrases that are not names. They are quantifier expressions. They are how many expressions. That's all right. This says there's exactly one number that's the number of the planets. And that number plus, well, there's exactly one number. That's the number of moons in the solar system. And the first number plus the second number, that gives you a prime number. I haven't put that very colloquially, but you see what I mean. Yeah. So that's all right. There's no names. There are just a couple of how many expressions. And Russell's point is when you've got expressions like that, they depend on a more basic way of thinking about the numbers. And that's given by the numerals. One, two, three, four, five. When you're learning arithmetic, when you're crying to teach a child arithmetic, you could not do it. It would be very ill-advised to do it not by counting, but by giving them terms like this. You couldn't explain what is a prime number means by telling a child, well, for example, the number of the planets plus the number of moons in the solar system. That's a prime number. If the child didn't have the numerals, you couldn't explain any other kind of talk about numbers to them. This is such a basic point that I'm not sure whether to labour it or not, or if I go too fast, I might make it totally incomprehensible. Can you just nod or raise a finger if that makes perfect sense? You couldn't do without the numerals. Yeah? Okay, thank you. Well, what that means is that the numerals are a kind of basic or canonical way of thinking about the numbers. Any fancier way of thinking about the numbers, like as the number of the planets, or the number of moons in the solar system, any more complex way of thinking about the numbers depends on this ground level way of thinking about each of them as one, two, three, four, five or whatever. Russell's point about our talk about the concrete world, about the people and the tables and chairs and so on, about the world revealed to us by the senses is that there has to be some analogue of the numerals. There's got to be the basic class of names for all those things that we're talking about. And that can't be explained in terms of descriptions or anything else. It's where language first gets going. It's the most basic kind of language there is. And his term for a kind of relation you have to stand in to the referent of a simple meme to be able to talk or think about it is acquaintance. So that's not to define acquaintance or say what it is. It's just some kind of encounter with the thing is what you need to be able to talk or think about it. Is that all right? So this needs much more discussion, but just the basic picture here, is that fairly straightforward? If I'm explaining it correctly, it should be fairly straightforward, so please stop me if it's not. Okay? And then you face these problems, these Freguian problems, about in terms of your basic class of names, how can you have informative identities in terms of your basic class of names? How could you have it being true that if this is one of your basic names and that is one of your basic names, how could you have an informative identity? This is that. How could you have meaning without reference? How could you have the possibility of saying truly this does not exist? And Russell says the only way you can solve these problems without appealing to sense is to suppose that this and that, your basic names are all talking about sensations or sense data, because at the level of sensations or sense data, of your own sensations or sense data, you can't have meaning without reference. If you're talking about this headache, there's going to be a headache there for you to be referring to, for you to know which thing you mean. And if you're talking about this headache, there is going to be no informative identity about it. This is true. With a concrete object, you can come at it from many angles. With something in your own inner life, there's no such thing as coming upon it from many angles. So you don't get this problem of informative identities. And if you feel like something is in your inner life, then it just is in your inner life. So you don't get the problem that it can seem to you for all the world as if there is such a thing that it's not really there. So to solve these problems of informativeness and meaning without reference, without appealing to sense or the idea of a definite description which belongs to a more sophisticated part of language, that Russell's driven to saying that ultimately all you're ever talking about are your own sensations, but that's to be trapped. We're now going to move to another part of the forest, but are there any questions about Russell's plight or Russell's insight? You might think that's the human condition, right? I mean, I think Russell did think that's just it. That's the human condition. That's why love is so important because it seems falsely to offer us a way out of our loneliness trapped behind our sense data. OK. Well, Cripkey's approach, ultimately though I won't really come on to this until next time, this is what I mean about moving to a different part of the forest, Cripkey's approach ultimately seems to offer a quite different kind of take. Cripkey's approach is consistent with saying there's a basic class of names in terms of which everything else is understood, but he's a quite different picture to how that basic class of names is going to work, what it's going to look like, than Russell does. And I just want to take quite a bit of time to shape up that picture. So I want to start out today by trying to explain what I think is the most difficult idea to get going in necessity if you haven't read this before, which is rigid designation, the idea that ordinary proper names are rigid designators. And here I said at the start it's good to keep flipping back and forth between doing the reading, listening to the lecture, doing the reading, going to section, listening to the reading again. Keep coming back to the reading because I'm not really going to comprehensively cover all that Cripkey says. I will try to cover what I think are the main and the harvest points. But it really will work best if you go back and forth. So I want to make a distinction between two kinds of possibility. One has to do with knowledge, one has to do with what's going on out there in the world independently of whether anyone knows about it. So two kinds of possibility, one relates to your current knowledge, the other relates to how things are in themselves. For example, suppose I come in to class a bit shaky and say to you indignantly you nearly knocked me off my bike sweeping up in your fancy car. Now you could easily have knocked me off my bike. Now when I say that I'm not saying for all I know you did knock me off my bike. I mean if I've been having a hard modelling then I might say that in some context but really that would be unusual. What I'm saying is I know perfectly well you didn't but you could have easily you nearly did. So there's that possibility that you knocked me off my bike and you might say no no no no I was miles away from you. You were just visibly a bag of nerves. I couldn't easily have knocked you off your bike. You could even have a row about what an easy possibility here and this might get really serious. What I mean is I could sue you for not taking due care. Watch out. But this has to do with possibilities. One of the things we do on ordinary life take this kind of possibility it doesn't have to do with what you know it has to be true. It has to do with out there in the real world what could easily have happened and what couldn't easily have happened. If you say about a nuclear reactor if you say look the three mile island reactor was only a hair away from causing a major causing thousands of deaths back in the 70s well that makes perfect sense but it might not. It could easily have happened or you might argue that couldn't easily have happened. What I'm saying is this kind of possibility doesn't have to do with what might be so given your current knowledge. In contrast suppose that you've got a murder investigation going on and you have the wise old chief inspector looking at the list of suspects and pointing to one and saying he could be our man that's to say what you mean there is for all we know that's the one that did it so this is a kind of possibility that does have to do with knowledge follow me very closely here suppose at the moment you think to yourself by God if only I had bunked off this class I could be on a beach in Marun right at this second if you have that terrible thought then it's not that you're thinking to yourself well for all I know maybe I am actually on a beach in Marun at the moment and this is all just a wonderful dream you see what I mean if you think I could be that's a kind of possibility that does not have to do with knowledge but this kind of possibility he could be our man maybe he actually is the guy who did it and you could have that with that example too if you woke up you were blindfolded and shoved in a car crunk then you might say well where am I then at that point you might say optimistically maybe I am on a beach in Marun you see what I mean what you mean there is like this it means for all I know maybe that's what's going on so these are two different kinds of possibility that he could be our man that would typically have to do with what might be so given your current knowledge whereas when you are talking about negligence or safety or risk there you are talking about not with what happens so far as you know but with metaphysical possibility when I say that thing about the reactor could easily have exploded it was negligent of people not to take better care of it or when I say you weren't really looking where you were going you could have killed me that's to do with metaphysical possibility I mean these two have different kinds of emotions associated with them take fear or apprehension or hope and fear has to do with stuff that for all you know it could still happen these are very emotional these things I might sound like some dry technical stuff but your whole emotional life is all about this kind of thing if you are hoping for something to happen that means you don't know whether it's happened or not but it's still possible that it might happen for all you know whereas regret relief, anger and wistfulness they all have to do not with epistemic possibility but with metaphysical possibility if I say if only I had married Jane everything would have been all right well that kind of wild cry of regret has to do with it's not that I think oh maybe I did marry Jane let's know what's going on what you're saying is there's a past possible world in which I do marry Jane and then that one everything turns out all right and similarly for relief if you think oh thank god I didn't marry Jane then what you're thinking is over there there's that possible world in which I do marry Jane and then everything turns out some other way okay so is that planar's day two kinds of possibility epistemic metaphysical what could be planar's in that okay it's important to get straight about this because for present purposes in this course we're largely not going to talk about epistemic possibility except for some very special cases we're going to focus on metaphysical possibility but it's important not to get the model up here are some new friends these are all the metaphysically possible worlds as you can see there are a lot of possible worlds and this is only really a small fraction actually there are probably infinitely many possible worlds and look here's us here's the actual world here's the world in which you didn't come to this class but you bunked off and did something else as you can see some of them are closer to the actual world than others so the world in which you bunked off and didn't come to this class that may be very far away you might say nothing on earth would have stopped me coming to this class on the other hand you might think god it was touch and go at UC Santa Barbara when you go into the philosophy department when you're driving on campus to the philosophy department you come to a fork in the road and one sign says philosophy department and the other sign says to the beach every morning you have to make that choice these new friends are just to make graphic so necessary will mean something like true in every one of them if you get 2 plus 2 is 4 then that will mean something like it's true in every possible world and that has nothing to do with what you know if you take some complex mathematical thing you might think well we don't know whether that's true or not you might be part of a team of mathematicians working on whether it's true or not and you say I'm terribly afraid this is going to work turn out that it's not true we should be such a disappointment for all we know it could still turn out not to be true that's consistent with saying that if it is true it's metaphysically necessary that it's true no you don't get that suppose I take some complex mathematical formula it's very complicated don't worry if you don't understand it all at first so it's a very complex formula you're part of a team you're trying to prove that this is true yes if this is true let's suppose it's a very hard sum let's suppose it's a really complicated long multiplication so we have a team and we're working in this now it's very hard to get this and you're hoping it's going to be an even number for reasons we won't go into but you wake up in the night thinking God maybe it's not an even number and that's epistemic for all you know it's not an even number but if it is an even number if the answer here is equals true if that whole thing is true then is it true in every possible world? yes it's true in every possible world how could it not be true in every possible world? it was a mathematical truth it's a mathematical truth and everybody every possible world will have to obey the laws of mathematics yes if 2 plus 2 is 4 that's true in every possible world so you might say well I don't know if this is true or not it could turn out to be false nonetheless it's metaphysically necessary it's true in every possible world if you got that last thing you got everything I've been saying yep so all this talk about possibility this is a little bit weird when I talk about possible worlds it's not very weird you kind of get what I'm saying but it's a little bit weird and the thing in real life that this corresponds to is talking about counterfactuals when I say there's a possible world in which you knock me off my back what I'm saying is if you had come just a little bit closer of I hadn't swerved like that you would have knocked me off my back yep so all this talk about possibilities to say if I were in this situation then that would happen yep so it's all about counterfactuals I'll come on to that in a second okay, plain as day is it necessary it's true in all metaphysically possible worlds what about a priori can you explain a priori in these terms a priori means something like what does a priori mean you can know it to be true without looking right so in the face of it you might think a priori if it's metaphysically necessary then you can know it's true without looking because you have to look in order to see which possible world you're in right for all you know when you're born you could be in any of those worlds yours this one that's A this one that's the actual world but if it's true in all metaphysical worlds then why would you need to look yes it does a priori is a notion of knowledge so you might think a priori means metaphysically necessary something like that it's a little bit delicate because the way we use the way we talk about what must be so epistemically if you say he must be our man that doesn't mean to say a priori it means given the knowledge we have it couldn't be that he's our man it's a little bit delicate what a priori has to do with epistemic possibility but it is an epistemic notion and that's why this is a little bit tricky and in fact but you see that straight off it seems like a priori must have something to do with what's metaphysically possible because suppose there's one metaphysically possible world in which it's not so then how can you know without looking that you're not in that world that seems kind of strange you see what I mean and there's one possible world in which it's not so then you need to look to see whether it is so because you might be in that world until you look you don't look quite so happy about that reasonably happy I was suggesting both yes I mean in the end we'll see that that's what I mean is right now when you think about it straight off it seems kind of reasonable to suppose that we're going to come to the same thing even though as I was pointing out they're defined in quite different ways and until Kripke I think everybody did think they can't be pretty much the same thing if you look in cell it seems to be taking it for granted that it's pretty much the same thing a priori unnecessary is something that cell says a number of times the way he's using it it seems like it's kind of rhetorical okay okay now what happens now is that we blow up the description theory of names from a somewhat different direction so start out thinking about counterfactual terms like if Germany had won the Second World War or if Al Gore had been the president to take both very poignant examples if Al Gore had been the president of the US in 2001 then we wouldn't have had all this nonsense say if Germany had won the Second World War then think of all the scientists and academics that would now be driving Germany okay so these are you can understand both of these these make sense in terms of possible worlds right so here you're looking at these possible worlds with Germany can I say one okay Germany had won the Second World War then okay then what you're looking at is some possible world which Germany wins the Second World War are some possible world in which Al Gore's president in 2001 so these have to do with metaphysical possibility they don't have to do with epistemic possibility I mean people write books about this scenario and they're not suggesting that well maybe Germany did win the Second World War right so what you're doing there is you do something like you describe a possible world in which Al Gore is the president of the U.S. in 2001 and you see what happens in that world so you take the Gore is president in 2001 if Gore had been president in 2001 let's take this world and then you're just describing what goes on in this possible world right that's a reasonable way to think of it so we've got two identifiers here we've got Al Gore and we've got the president of the U.S. in 2001 so in the actual world in this world Al Gore designates one guy and the president of the U.S. in 2001 that designates someone else someone else who uniquely fits that description right who is it George W. Bush right so the actually George W is what's designated by the description here Al Gore designates a quite different person so what we're considering here is a world in which they designate the same person yeah okay so in this world let's suppose it's this world where Gore is president in 2001 then does the name Al Gore designate the same person in this world as it does in this world no? yes that's what you're doing you're looking at poor old Al actually there could be a better example but anyway you're looking at poor old Al who's over this feet up over the fire going on about what could have happened if only and you say well what would have happened if he had been president in 2001 you're talking about that person and asking what would have happened if they'd won that election yeah so it's going to be the same person but consider the president of the US in 2001 when we're considering this scenario does that description designate the same person in this scenario as it does in this scenario no right because in the actual scenario it designates George W in this scenario it's designating Al Gore yes okay and this is general when you're talking about any possible world if you're saying if Al had learned to play timpani he could have been a great performer you're still talking about that same person in a different possible world yeah that's what the name does it kind of grabs on to a person unless you think about what would have happened to them in lots of different situations whereas a description like the president of the US that's a role that's a role that someone might fill and different people can fill that role in different possible worlds how should I put this being Al Gore is not really being John Malkovich is not really it's kind of a joke because the such a thing is the role of being president of the United States but being Al Gore or being John Malkovich that's not really a role that many people could fill I mean there's only one it doesn't really make sense to talk about as if it's a role that lots of people could fill so for any other world that you're talking about when you're talking about any other possibility Al Gore refers to just the same person as it does in this world the description, the president of the US there are lots of people who could fill that role Ron Paul, you're me I mean you can imagine any kind of counterfactual situation yeah to lots of different people could fill that so what's going on there is that you take names I mean this is quite general it's not that it's something special about the name Al Gore you take names you use the name to keep crack of the same object in different possible situations when you're talking about what could have happened to someone if you say if only I had the opportunities I could have been a great violinist if only they hadn't all been so mean to me I'd be a nice person today if you, what you're doing there is you're using the designator to lock on to the person and then say what would have happened to that person in all these other situations but a description does something different a description identifies a general role and in different counterfactual situations in different possible worlds different individuals can occupy that role so there's another big difference between names and descriptions names have got that lock on to the thing and then talk about what could have happened to it descriptions aren't working like that can you put it up your hand if that's okay if it's not okay you've got a chance to complain right now okay alright so if you've got that then the doctrine of rigid designation is easy Cribci says let's call something a rigid designator if in every possible world it designates the same object so class do we have any examples of rigid designators can we think of any any term that might meet that definition Algor as it might be and indeed any name is going to work like that if he changes his name that's right Algor might not have been called Algor no question about that but would he still be Algor that is the issue he'd be a really different but just think about that formulation he'd be a really different person well of course it's language no I just mean you've got to use language when you're talking if you see what I mean you've got to have a when you say he'd be a really different person you're assuming a sense in which is one in the same thing that exhibiting all these different characteristics in another possible world so you've got to have that lock on I mean you're not just saying well there could be somebody different there you see what I mean I mean the sense it does make sense to say it wouldn't be Algor in different counterfactual situations and what I mean is suppose you say well suppose he'd drunk some magic potion that turned him into a butterfly then you can imagine a situation in which someone drinks a magic potion and the person is killed and a butterfly replaces them and their selves are used to make a butterfly so there's two different things there the person and the butterfly but it's natural to think can it really make sense if that being the same person of the butterfly being Al surely that wouldn't be Al you see what I mean it might be made from Al cells but look if Al just changes his name if he's not called the Al that's not going to be enough to make him a different person if he's just got a different name I mean if only it was so easy I mean otherwise change of name would really be pretty radical when I'm using the name right now I mean this is an important point this thing when I'm using the name right now when I'm using the name I'll go right now I'm using it to denote one in the same person in all these different situations it doesn't matter whether they're called I'll go in all these different situations all it matters is that that's the person my use of the word now designates and I'm I'm using that to keep crack of them through all these different situations and that includes situations for the change of name or nobody speaks English or there's no language at all yeah what about that yes reference point that's where we are yeah we're in the actual world yeah that's a kind of apriori we're in the actual world whatever world this is that's the actual one yeah aha that's a fair next move that is like the next move on and I think that is very much Cripty's picture the name is a simple tag for the object and his task is just to keep tagging that object whichever world you're talking about whatever strange transformations that object might be undergoing or going as you'd travel through counterfactual space yeah okay okay so in any world the name I'll go is going to be referring to just the same person whether it's changed their name or not whether they're called I'll go in that world or not whereas a description is describing a role that different people can play in different counterfactual situations we're using names to keep crack of the same object across different possible situations whereas a descriptions identifying a general role and as you travel across the possible worlds different objects will fill that role and so a rigid designator is one in which in every possible world designates the same object so so long as you hold constantly the meaning of the sign and so long as you don't suddenly start using I'll go to mean my pink toothbrush or whatever so long as you hold constantly the meaning of the sign whenever you're using a name to specify a possible world it always refers to the same object that's the value of names in counterfactual thinking so I'll go is a rigid designator as you said designates the same thing in different possible worlds you can talk about the designation of a definite description when you say there's exactly one object which is f the definite description vf designates that object so it's not true reference but you can talk about designation here so definite descriptions are going to designate different objects in different possible worlds the president of the US in 2001 is going to designate different people all, you, me, yeah and then reference the father that makes perfect sense you could construct a language of what like that but the thing is even in that world suppose that some of Aristotle's contemporaries are talking about him you're looking right at him and you say well of course he owes it all to his father Aristotle owes it all to his father it's his father that got him to where he is if it hadn't been for the influence of his father he wouldn't have had a chance he's no better than you or me they say I mean this is just academic life it's just luck and influence that's got him there that's what they're saying in your language they wouldn't have a way of expressing that you know if they try to say Aristotle wouldn't have been where he was without his father they suddenly start talking about his father and they're saying that his father wouldn't have been where he was without his father but that's not what they meant to be saying they meant to be saying something about this one right in front of them so you could have a language like yours but it would be impoverished there would be things you do want to say that you couldn't say in your language although I suppose if Aristotle had a son you might get the effect you want you might get the effect you want that's right when you're talking about when you're talking about the different possible world you'd have to be able to designate the son in the actual world and then shifting out to the other possible world talk about the father what was going on with the father in that world but how should I say it at the very least it would be cumbersome very hard to follow what was going on but how should I say it it would be very hard to follow what was going on and you might not be able to do it at all if Aristotle didn't have a son this is just kind of descriptive linguistics really it's just saying this is how the names work in our language this is just describing what goes on in our language so it doesn't really have any more authority than that and I think you're completely right it is worth thinking about languages where something different happens because it helps bring out whether there is anything deep about this fact about our language so that you couldn't change it easily you need a lot longer discussion but of the same kind that we've just been having yet to get at that but so far it's just presented as something that this is actually I mean this is how in fact names work in our language yeah okay so see yeah I think it goes pretty far it stretches to everything conceivable I think everything genuinely conceivable my basic point about the counterfactuals though is that we have a way of understanding counterfactuals in ordinary life that doesn't really depend on having some analysis of what possibility is when I say to you you nearly knocked me off my back you could easily have not if I'd been a bit closer you'd have knocked me off my back we can argue about that counterfactual perfectly well and if you back off and say yeah but are you talking about conceptual possibility I'm gonna say okay that's it I'm suing you see what I mean we don't really we have a way of talking about counterfactuals that is quite how should I say grounded in that it doesn't depend in some analysis I don't at all mean to deny that there are interesting questions about how you give an analysis of it but what I mean is in just common sense life in everyday life we do understand this talk of possibilities perfectly well in terms of counterfactuals yeah okay so remember Fregis version of the description theory was Aristotle just means it has the same sense as the last great philosopher of antiquity and if not this one then some other description but if everything I've said so far has been right could that be true it can be true is this one a rigid designator is this one a rigid designator therefore can they have the same meaning no they're different meanings therefore it's just a mistake to suppose that names can be equivalent to descriptions yeah Aristotle refers to the same thing in every possible world the last great philosopher of antiquity refers to different things in different possible worlds therefore they have different meanings and of course it's not going to help if you move to thinking of a bag or a cluster of descriptions because the whole cluster of descriptions is going to be whatever the opposite of rigid is flexible I guess they're going to refer to different things designate different things in different possible worlds so even if you set aside Russell's point for the moment names can't mean the same thing as descriptions a name doesn't have the same meaning of a description so when Frega said you get the sign you get the description fixing reference and you get the reference to the sign that picture just because of these considerations has to be incorrect and as someone said a moment ago this kind of picture when the name is just locking onto the object so you can keep tabs on that object in thinking about it counterfactually through different situations that seems a much more appealing picture here but now notice that something I'm sorry we've only got a couple of minutes to go so let me get to my punchline such as this is and if there's time then take questions if you take Hesperus as the brightest thing in the morning sky that's not true in all possible worlds that might be true in this world but you can imagine other worlds in which there's an extra star there but suppose you take Hesperus as phosphorus suppose you take any identity statement Bruce Wayne is Batman any identity statement involving two proper names these are both rigid designators so both of them identify the same thing in every possible world so is that a necessary truth well necessary means true in all possible worlds the two of them refer to the same thing in every possible world so you're not going to find a possible world in which Hesperus refers to one thing and Phosphorus refers to another so Hesperus and Phosphorus in every world refer to the same thing as each other so that statement is necessary if it's true that Bruce Wayne is Batman it's necessary that Bruce Wayne is Batman take anyone who has got two names those two names the identity you frame using those two names is necessary but it's not going to be a priori so how did that happen if it's necessary how come you need to look but if I've stated this right the argument so far should be completely compelling how can there be necessary truths that are not a priori remember I said it's very natural to take it that the two of them go together several takes it that the two I mean several was writing before krypci of course but everyone took it before krypci that the two of them go together quickly I think the bell is gone quickly that would make it go away if somehow in the name Hesperus there was the name Phosphorus but the whole trouble is it's not you stand there looking at the morning sky and you say call it Hesperus you look at the evening sky you say call it Phosphorus you have no idea whether they are the same you formulate the identity statement it's Phosphorus you just stated something that's a necessary truth and you have no way of finding it out within a lot further observation we really have to stop at this point we'll pass the hour more in this next time