many thanks! 11:00 properties 13:00 coextensive properties 14:15 to accept modal realism 14:55 possible worlds and metaphysics of events 15:00 utility of possible worlds 16:20 possible worlds for philosophy(benefits of modal realism) 20:55 if we reject modal realism 22:00 scientific theories & modal realism 24:42 wecan not interact w/possible worlds/spatio-temporal isolated 27:10 fictionalism-depends on us & collapses into realism 32:20 abstracts/ersatz , linguistics just finished Kant's critique of pure reason!
If something is possible, but not actual in some universe, i feel like that would need a special explanation. It seems "simpler" to me for everything possible to exist, than for some subset of possible things to exist. That'd be my metaphysical argument for this. I don't see how we could provide evidence beyond broad arguments like that.
This video is in desperate need of a definition for "exists". What exactly is Platonism saying when it says that numbers exist? Calling it _literal_ existence offers no clarification. What would figurative existence be for numbers? I can comprehend a difference between Sherlock Holmes and Barack Obama and that difference is what makes Barack Obama exist while Sherlock Holmes does not exist. In order to comprehend the existence of numbers, I would like to compare the existing numbers to some fictional numbers so I can see the difference between existing and not existing for numbers. "Numbers are indispensable to our best theories of the world." This is a very odd premise. I would have said that numbers are indispensable to our _descriptions_ of our best theories of the world, in the sense that we would have difficulty describing many scientific theories without numbers. The theories are not postulating numbers; they are just using numbers as a descriptive tool. That wouldn't normally count as an endorsement of the actual existence of a thing. For example, if I have a true theory that can be best explained by telling a story about Sherlock Holmes, that does not justify believing that Sherlock Holmes is a real person. "This seems to make possibility dependent on us. We control fictions; we decide what fictions say." Modal realism is in exactly the same situation, so that is not a special weakness of fictionalism. By the nature of possible worlds in modal realism we have no way to investigate those worlds. When we say that there is a possible world where Hitler won the war, it is not because we have visited the real place where this happened. On the contrary, that other world is forever beyond our reach no matter how real it may be. When we talk about such possible worlds we are telling a story about a place we have never seen, and then convincing ourselves that this place is real. That is just as much dependent on us as any fiction. "According to the possible worlds fiction, it is true at every possible world that all possible worlds exist." Wouldn't the fictionalist consider all statements about possible worlds to be fiction, even within other possible worlds? Possible worlds ought to still be fiction no matter which world we're in, so the actual world would be a fictional world when considered from some other possible world. In that case, the statement would be read as: _According to the possible worlds fiction, it is true at every possible world that according to the possible worlds fiction all possible worlds exist._ That would entail: Necessarily, according to the possible worlds fiction, all possible worlds exist. Regarding linguistic ersatzism, the problem of defining impossible worlds is not clear. Obviously the impossible worlds are those worlds which imply a contradiction. Is this the presupposition that is supposed to be a problem? As for the limited possibilities of linguistic ersatzism, even if it is limited by our language, that is still always going to be enough possible worlds to deal with any philosophical issue that we could ever want to use possible worlds to solve. The problems that are beyond the reach of linguistic ersatzism are also beyond the reach of our ability to describe, and when we expand our ability to describe problems, we also expand the reach of linguistic ersatzism. The problem of A-matter and B-matter swapping roles is unclear. Obviously to describe a world of A-matter and B-matter you need to include statements describing the distribution of A-matter and B-matter in the world. Then in a world where A-matter repels and B-matter attracts, you end up with repulsion in all the places there would have been attraction. That seems like a pretty huge distinction! Perhaps when A-matter and B-matter swap roles, they also swap positions so that all the A-matter of the second world is in the place of all the B-matter in the first world. In the case, not only is A-matter repelling, but it is also in the exact place of the B-matter. In this case, how can we justify asking linguistic ersatzism to distinguish these two worlds when the two worlds seem identical in every respect?
+Ansatz66 Thanks for the comment. I'm not sure how helpful it would be to get into the debates about how to define "existence". All I would say is that when the platonist says "numbers exist", he's using "exist" in the same way as when I say "tables and chairs exist" or when a theist says "God exists". There *really are* numbers. Furthermore, the platonist thinks that numbers are mind-independent. Emotions exist, but emotions are part of our minds. Some people might even think that Sherlock Holmes exists, but Sherlock Holmes exists as an idea in our minds. Not so for numbers, according to the platonist. Numbers would be there whether or not any beings had ever conceived of them. Re the indispensability argument, I explain it in more detail in my video on platonism (see 22:50): ua-cam.com/video/YxgH5ykGwdQ/v-deo.html I think that Quine and Putnam would say that the fact that numbers are merely being used as a descriptive tool, as you say, isn't really relevant, since the question then becomes "why does that descriptive tool work so well?" They would also say that if our best theories of the world worked by telling a story about Sherlock Holmes, in the same kind of way as our best theories use mathematics, then that *would* justify believing in Sherlock Holmes. For what it's worth, I don't buy the indispensability argument. As I pointed out, an important reason that we believe in electrons and photons and mitochondria is that we can *interact* with them - we can't interact with abstract mathematical entities. (I also agree with Penelope Maddy's criticisms of the indispensability argument; again, see the platonism video.) "Modal realism is in exactly the same situation..." I disagree that modal realism makes possibility dependent on us. The modal realist thinks that possible worlds are really out there, and they are what they are regardless of what we think about them. I think what you're getting at is the epistemological problem of: given modal realism, how could we ever know anything about modality, since the facts about modality are completely isolated from us? We can never interact with other possible worlds, so how can we have any justified beliefs about them? That's a very important problem, and I intend to look at it when I do a video on the objections to modal realism. But I don't think it's the same problem as the fictionalist faces, that possible worlds end up being too artificial to capture the facts about modality. "Wouldn't the fictionalist consider all statements about possible worlds to be fiction, even within other possible worlds?" No. Think about it this way: it's fictional that the Simpsons live at Evergreen Terrace, but *within the fiction of the TV show The Simpsons*, it's true that the Simpsons live at Evergreen Terrace. In other words, according to the story told by the TV show The Simpsons, it's true that the Simpsons live at Evergreen Terrace. To say that, according to the story told by the TV show The Simpsons, it's fictional that the Simpsons live at Evergreen Terrace, would imply that we have a "story within a story". This is the case for the Itchy and Scratchy show, a fictional TV show that characters within the The Simpsons watch. According to the story told by the TV show The Simpsons, it's fictional that a blue mouse called "Itchy" repeatedly kills a black cat called "Scratchy". (I hope that makes sense. It might not if you haven't seen The Simpsons.) Similarly, according to the possible worlds fiction, all possible worlds exist. It's not really true that all possible worlds exist, but it is true *within the possible worlds fiction* that all possible worlds exist. To say that, within the possible worlds fiction, it's fictional that all possible worlds exist, would imply that possible worlds are a "story within a story" like the Itchy and Scratchy show. That's not what the fictionalist is saying. For the fictionalist, possible worlds are just a fictional story, not a story within a story. "Obviously the impossible worlds are those worlds which imply a contradiction" Well, (a) there might be things that are impossible that don't imply contradictions and (b) perhaps some contradictions aren't impossible. Graham Priest thinks that there are true contradictions, so he wouldn't accept that a world that implies a contradiction is an impossible world. Of course, you can certainly defend the claim that the impossible is whatever implies a contradiction. The real problem for linguistic ersatzism, according to Lewis, is that the linguistic ersatzist can't reduce the modal to the non-modal, but the modal realist can. On linguistic ersatzism, impossible worlds, however the impossible is defined, are exactly the same kind of thing as possible worlds (both possible and impossible worlds are sets of propositions). So linguistic ersatzism needs some prior distinction between possibility and impossibility. The modal realist says: X is possible iff it X occurs at some world. So he can reduce modal facts to non-modal facts. The linguistic ersatzist can't do that. "Obviously to describe a world of A-matter and B-matter you need to include statements describing the distribution of A-matter and B-matter in the world. Then in a world where A-matter repels and B-matter attracts, you end up with repulsion in all the places there would have been attraction. That seems like a pretty huge distinction!" The problem is with the very idea that A-matter and B-matter could swap roles given linguistic ersatzism. Yes, the worlds are different in terms of the distribution of repulsion and attraction. The question is, how do you know that you're talking about a world where A-matter and B-matter have swapped roles, rather than world where the distribution of A-matter and B-matter is different? The difficulty is about how we specify what A-matter and B-matter are. For what it's worth though, I'm inclined to agree with you that linguistic ersatzism provides enough possible worlds for any practical purpose, so this isn't really a serious problem. If it turns out that, given linguistic ersatzism, we have difficulty dealing with worlds with completely alien properties, I think the linguistic ersatzist should just bite the bullet and insist that such alien properties aren't really possible, contrary to what our intuitions might be.
Kane B "All I would say is that when the platonist says 'numbers exist', he's using 'exist' in the same way as when I say 'tables and chairs exist' or when a theist says 'God exists'." Indeed, this is quite unhelpful. Numbers are clearly a different category of thing than tables, chairs, and God. Saying that numbers exist in the same way that chairs exist is like saying my emotions are blue in the same way that cerulean paint is blue. Am I saying that my emotions are visible? In the same way, are platonists saying that numbers are tangible objects like chairs? Sadly, that's not what we mean, though that would clarify the issue. That numbers would continue to do this incomprehensible thing with or without minds is also remarkably uninformative. "It is true within the possible worlds fiction that all possible worlds exist." That's true, but what about within each possible world of the possible worlds fiction? Each possible world obviously has a set of things which are true. The question is, within the possible worlds of the possible worlds fiction, are the other possible worlds real or are they like Itchy and Scratchy, a fiction within a fiction? If from within the fiction the other possible worlds are still fictional, then "According to the possible worlds fiction, it is true at every possible world that all possible worlds exist," is not really collapsing fictionalism into realism because it's just talking about a fiction within the fiction. Surely a fictionalist would imagine possible worlds where fictionalism applies. "How do you know that you're talking about a world where A-matter and B-matter have swapped roles, rather than world where the distribution of A-matter and B-matter is different?" So we're essentially constructing two worlds that are the same in every conceivable way, and then asking how linguistic ersatzism can distinguish them. In such a situation, if we decide that linguistic ersatzism cannot distinguish the two worlds then we're really saying that linguistic ersatzism entails the identity of indiscernables for possible worlds. "I think the linguistic ersatzist should just bite the bullet and insist that such alien properties aren't really possible." On the contrary, the linguistic ersatzist should insist that indescribable alien properties are possible. If something is indescribable it can only mean that we don't have the linguistic tools to talk about it, but new words can always be invented, and as soon as we invent the necessary words the indescribable alien properties must inevitably become describable, at which point they would have to be called possible by the linguistic ersatzist. So if the linguistic ersatzist is going to make any comment at all about indescribable properties the comment should be that they are possible, or else the linguistic ersatzist must allow things to jump between impossible and possible. On the other hand, if the so-called alien property is not an actual alien property at all and is in fact pure nonsense, then the reason it cannot be described is because there is nothing to describe. In this case, it's not fair to say that we are talking about an alien property and the real question is: Is a pure nonsense property possible under linguistic ersatzism? This is when the linguistic ersatzist should bite the bullet and insist that pure nonsense isn't really possible.
+Ansatz66 Strictly speaking, I'm not sure I'd say that there are different kinds of existence. Certainly the platonist need not say that. The standard platonist thinks that numbers exist, just like chairs exist, or oceans exist, or electons exist, or whatever (chairs are very different from oceans, but we don't usually say that chairs and oceans have a different kind of existence). As for what kind of thing numbers are - according to the platonist, they're abstract objects. In this respect, they're very much unlike chairs. What exactly does it mean to say that numbers are abstract objects? On this, I can't really help you. I'm not inclined to accept platonism. One of the reasons why I'm not inclined to accept platonism is that the notion of abstract objects has never made much sense to me. Often, abstract objects are defined in terms of what they're not. They're not spatiotemporal, they're not capable of entering into causal relations, they don't undergo change, etc. You might object that this isn't very informative. I agree. "That's true, but what about within each possible world of the possible worlds fiction? Each possible world obviously has a set of things which are true. The question is, within the possible worlds of the possible worlds fiction, are the other possible worlds real or are they like Itchy and Scratchy, a fiction within a fiction?" The former. Perhaps you could interpret modal fictionalism in the way that you suggest. I don't think this would be a popular option though, because it's straightforwardly inconsistent. On your interpretation, the possible worlds fiction says: all possible worlds exist, and at each possible world, it's a fiction that all possible worlds exist. (Maybe inconsistency isn't such a big deal here, though... it is a fiction, after all.) "So we're essentially constructing two worlds that are the same in every conceivable way, and then asking how linguistic ersatzism can distinguish them" The point of the objection is that possibilities outstrip what can be described, so in a certain sense the worlds are identical in terms of what we can conceive about them. Maybe a different example would be helpful. Consider colours. We might say that it's possible for there to be more colours than there are. It doesn't seem to be logically contradictory for there to be more colours, at any rate. (If you disagree with this, well, just play along for the sake of argument; I'm sure you can substitute a different example). Call one of these alien colours "A" and the other "B". Since A and B don't exist in the actual world, we never have any contact with them. So the only way the linguistic ersatzist can capture them is to describe them. Maybe this can be done. Maybe A is yellow-blue and B is red-green, two colours that, arguably, can't exist in the actual world. Fair enough. But, presumably, there could be many more colours than this. There could be colours that simply outstrip what we can have the capacity to describe. Colours that we can't imagine, colours that are simply outside of our experience and aren't formed by combinations of colours that we're familiar with. So call two of these colours that we can't describe "C" and "D". Now consider two worlds that are identical except for the distribution of colours. In one world, all planets are C and stars are D, in the other, all planets are D and all stars are C. The objection is that these situations are possible, and they are different possibilities, but the linguistic ersatzist can't distinguish them. Sure, she can say of one world "all planets are C and all stars are D". But "C" and "D" are just placeholders. The linguistic ersatzist needs to give an actual description of these colours in order to distinguish the worlds, but as noted, these are among the colours that outstrip what we can describe. The placeholders are the best she can do. "On the contrary, the linguistic ersatzist should insist that indescribable alien properties are possible" That would just be to give up linguistic ersatzism. To be possible, for the linguistic ersatzist, *just is* to be described within a set of maximal consistent propositions. So lingistic ersatzists certainly can't say that *indescribable* alien properties are possible. "and as soon as we invent the necessary words the indescribable alien properties must inevitably become describable" It's not really a matter of what words we have. I didn't get into this in the video, but linguistic ersatzists don't usually take the set of propositions to be English. Anyway, propositions are meanings of sentences, hence often taken to be independent of any language. "Snow is white" and "Schnee ist weiss" both have the same meaning, i.e. they both express the same proposition.
Kane B "One of the reasons why I'm not inclined to accept platonism is that the notion of abstract objects has never made much sense to me." Surely one need only talk to a platonist and discover what they think they mean by the existence of abstract objects. Doing so seems the least we should do before passing judgement on that philosophy. The principle of charity demands that we not reject a philosophy until we understand it. I can interpret platonism in a way that makes sense to me. Since an abstract object obviously cannot be tangible in the way that a chair is tangible, an abstract object cannot fully exist in the way that a chair would be said to exist. In this situation, I think the only way to make sense of platonism is to assume that we aren't using the word "exists" in the same sense for abstract objects as they would for chairs. An abstract object could just mean an idea, and to say that an abstract object exists is just to say that it is an idea that someone could potentially have. "I don't think this would be a popular option though, because it's straightforwardly inconsistent." The only way we can have an inconsistency is if there is a contradiction within a particular world. When I am constructing my possible worlds fiction, I am absolutely free to assign any truth value to any proposition so long as I do not imply a contradiction, and saying that possible worlds are fictional does not imply a contradiction. Having every world agree that possible worlds are fiction _especially_ does not imply a contradiction. "On your interpretation, the possible worlds fiction says: all possible worlds exist, and at each possible world, it's a fiction that all possible worlds exist." I guess that the contradiction we are trying for is that the fiction of our world is inconsistent with the truth in the other possible worlds. That's strange since no one ever expects fiction to be consistent with truth, especially across multiple possible worlds. "Propositions are meanings of sentences, hence often taken to be independent of any language." Good point. I see I was confused on that issue. The talk of alien properties made me think that the properties were indescribable due to being alien to our language, but to be indescribable by language-independent propositions is another thing entirely. "There could be colours that simply outstrip what we can have the capacity to describe." Since we're being language-independent, we can't use the limits of English to define our capacity to describe things. Those colors may be alien to us, but we ought to be allowed to use a language that would be used by the possible people who can see those colors. "To be possible, for the linguistic ersatzist, just is to be described within a set of maximal consistent propositions." Since I now see that the propositions of linguistic ersatzism are language independent, in order to show that there are possibilities beyond the possibilities of linguistic ersatzism we need to show that some possibility cannot be expressed in _any_ language, no matter how alien that language might be. This seems very challenging, and neither the matter examples nor the color examples seem to clearly establish this point.
+Ansatz66 It's not that I'm unfamiliar with platonism. I have a long video that examines platonism in some detail: ua-cam.com/video/YxgH5ykGwdQ/v-deo.html Re your suggestion, ideas in the mind are fine. That makes sense. But that's not platonism. A crucial elemnt of the platonist account is that mathematical objects are mind-independent. "The only way we can have an inconsistency is if there is a contradiction within a particular world." I disagree. Suppose that in one world, "necessarily all swans are blue" is true. Suppose that in another world, "necessarily all swans are blue" is false. In this case, there's no contradiction *within* any particular world, but given how possible worlds discourse works, this is contradictory. The truth in the first world entails that all swans are blue at all worlds at which there are a swans; the truth in the second world entails that in some worlds in which there are swans, some swans are not blue. In other words, in the worlds containing swans, it both is and is not the case that all swans are blue. The problem with your version of fictionalism is that the fiction says both that all possible worlds exist, but also no possible worlds exist except the possible world that we happen to be talking about at the time (because, at each possible world, every other possible world is merely fictional). That's inconsistent. As I said though, maybe that's not really a problem; maybe the inconsistency doesn't matter because it's only a fiction. "we ought to be allowed to use a language that would be used by the possible people who can see those colors." On linguistic ersatzism, there is no such language though. It's no good appealing to to "possible people" because there are no possible people. The linguistic ersatzist has to construct possible worlds using only the resources available in the actual world (that's why linguistic ersatzism is classed as a form of actualism - possible worlds are constructions out of what actually exists). "This seems very challenging, and neither the matter examples nor the color examples seem to clearly establish this point.?" I agree with that. Knockdown refutations are very rare in philosophy. There's always a response to any argument. I doubt anybody could come up with an argument that conclusively shows that linguistic ersatzism fails to capture all the possibilities.
many thanks!
11:00 properties
13:00 coextensive properties
14:15 to accept modal realism
14:55 possible worlds and metaphysics of events
15:00 utility of possible worlds
16:20 possible worlds for philosophy(benefits of modal realism)
20:55 if we reject modal realism
22:00 scientific theories & modal realism
24:42 wecan not interact w/possible worlds/spatio-temporal isolated
27:10 fictionalism-depends on us & collapses into realism
32:20 abstracts/ersatz , linguistics
just finished Kant's critique of pure reason!
Thanks
I love it! What is the mass of the Earth? I actually don't know the mass of the Earth bad example.
11:30 "but it has a mass"
If possible worlds exist, are some of them non-actual entities?
If something is possible, but not actual in some universe, i feel like that would need a special explanation. It seems "simpler" to me for everything possible to exist, than for some subset of possible things to exist. That'd be my metaphysical argument for this. I don't see how we could provide evidence beyond broad arguments like that.
Great video
This video is in desperate need of a definition for "exists". What exactly is Platonism saying when it says that numbers exist? Calling it _literal_ existence offers no clarification. What would figurative existence be for numbers? I can comprehend a difference between Sherlock Holmes and Barack Obama and that difference is what makes Barack Obama exist while Sherlock Holmes does not exist. In order to comprehend the existence of numbers, I would like to compare the existing numbers to some fictional numbers so I can see the difference between existing and not existing for numbers.
"Numbers are indispensable to our best theories of the world."
This is a very odd premise. I would have said that numbers are indispensable to our _descriptions_ of our best theories of the world, in the sense that we would have difficulty describing many scientific theories without numbers. The theories are not postulating numbers; they are just using numbers as a descriptive tool. That wouldn't normally count as an endorsement of the actual existence of a thing. For example, if I have a true theory that can be best explained by telling a story about Sherlock Holmes, that does not justify believing that Sherlock Holmes is a real person.
"This seems to make possibility dependent on us. We control fictions; we decide what fictions say."
Modal realism is in exactly the same situation, so that is not a special weakness of fictionalism. By the nature of possible worlds in modal realism we have no way to investigate those worlds. When we say that there is a possible world where Hitler won the war, it is not because we have visited the real place where this happened. On the contrary, that other world is forever beyond our reach no matter how real it may be. When we talk about such possible worlds we are telling a story about a place we have never seen, and then convincing ourselves that this place is real. That is just as much dependent on us as any fiction.
"According to the possible worlds fiction, it is true at every possible world that all possible worlds exist."
Wouldn't the fictionalist consider all statements about possible worlds to be fiction, even within other possible worlds? Possible worlds ought to still be fiction no matter which world we're in, so the actual world would be a fictional world when considered from some other possible world. In that case, the statement would be read as: _According to the possible worlds fiction, it is true at every possible world that according to the possible worlds fiction all possible worlds exist._
That would entail: Necessarily, according to the possible worlds fiction, all possible worlds exist.
Regarding linguistic ersatzism, the problem of defining impossible worlds is not clear. Obviously the impossible worlds are those worlds which imply a contradiction. Is this the presupposition that is supposed to be a problem?
As for the limited possibilities of linguistic ersatzism, even if it is limited by our language, that is still always going to be enough possible worlds to deal with any philosophical issue that we could ever want to use possible worlds to solve. The problems that are beyond the reach of linguistic ersatzism are also beyond the reach of our ability to describe, and when we expand our ability to describe problems, we also expand the reach of linguistic ersatzism.
The problem of A-matter and B-matter swapping roles is unclear. Obviously to describe a world of A-matter and B-matter you need to include statements describing the distribution of A-matter and B-matter in the world. Then in a world where A-matter repels and B-matter attracts, you end up with repulsion in all the places there would have been attraction. That seems like a pretty huge distinction!
Perhaps when A-matter and B-matter swap roles, they also swap positions so that all the A-matter of the second world is in the place of all the B-matter in the first world. In the case, not only is A-matter repelling, but it is also in the exact place of the B-matter. In this case, how can we justify asking linguistic ersatzism to distinguish these two worlds when the two worlds seem identical in every respect?
+Ansatz66 Thanks for the comment. I'm not sure how helpful it would be to get into the debates about how to define "existence". All I would say is that when the platonist says "numbers exist", he's using "exist" in the same way as when I say "tables and chairs exist" or when a theist says "God exists". There *really are* numbers. Furthermore, the platonist thinks that numbers are mind-independent. Emotions exist, but emotions are part of our minds. Some people might even think that Sherlock Holmes exists, but Sherlock Holmes exists as an idea in our minds. Not so for numbers, according to the platonist. Numbers would be there whether or not any beings had ever conceived of them.
Re the indispensability argument, I explain it in more detail in my video on platonism (see 22:50):
ua-cam.com/video/YxgH5ykGwdQ/v-deo.html
I think that Quine and Putnam would say that the fact that numbers are merely being used as a descriptive tool, as you say, isn't really relevant, since the question then becomes "why does that descriptive tool work so well?" They would also say that if our best theories of the world worked by telling a story about Sherlock Holmes, in the same kind of way as our best theories use mathematics, then that *would* justify believing in Sherlock Holmes. For what it's worth, I don't buy the indispensability argument. As I pointed out, an important reason that we believe in electrons and photons and mitochondria is that we can *interact* with them - we can't interact with abstract mathematical entities. (I also agree with Penelope Maddy's criticisms of the indispensability argument; again, see the platonism video.)
"Modal realism is in exactly the same situation..."
I disagree that modal realism makes possibility dependent on us. The modal realist thinks that possible worlds are really out there, and they are what they are regardless of what we think about them. I think what you're getting at is the epistemological problem of: given modal realism, how could we ever know anything about modality, since the facts about modality are completely isolated from us? We can never interact with other possible worlds, so how can we have any justified beliefs about them? That's a very important problem, and I intend to look at it when I do a video on the objections to modal realism. But I don't think it's the same problem as the fictionalist faces, that possible worlds end up being too artificial to capture the facts about modality.
"Wouldn't the fictionalist consider all statements about possible worlds to be fiction, even within other possible worlds?"
No. Think about it this way: it's fictional that the Simpsons live at Evergreen Terrace, but *within the fiction of the TV show The Simpsons*, it's true that the Simpsons live at Evergreen Terrace. In other words, according to the story told by the TV show The Simpsons, it's true that the Simpsons live at Evergreen Terrace. To say that, according to the story told by the TV show The Simpsons, it's fictional that the Simpsons live at Evergreen Terrace, would imply that we have a "story within a story". This is the case for the Itchy and Scratchy show, a fictional TV show that characters within the The Simpsons watch. According to the story told by the TV show The Simpsons, it's fictional that a blue mouse called "Itchy" repeatedly kills a black cat called "Scratchy". (I hope that makes sense. It might not if you haven't seen The Simpsons.)
Similarly, according to the possible worlds fiction, all possible worlds exist. It's not really true that all possible worlds exist, but it is true *within the possible worlds fiction* that all possible worlds exist. To say that, within the possible worlds fiction, it's fictional that all possible worlds exist, would imply that possible worlds are a "story within a story" like the Itchy and Scratchy show. That's not what the fictionalist is saying. For the fictionalist, possible worlds are just a fictional story, not a story within a story.
"Obviously the impossible worlds are those worlds which imply a contradiction"
Well, (a) there might be things that are impossible that don't imply contradictions and (b) perhaps some contradictions aren't impossible. Graham Priest thinks that there are true contradictions, so he wouldn't accept that a world that implies a contradiction is an impossible world.
Of course, you can certainly defend the claim that the impossible is whatever implies a contradiction. The real problem for linguistic ersatzism, according to Lewis, is that the linguistic ersatzist can't reduce the modal to the non-modal, but the modal realist can. On linguistic ersatzism, impossible worlds, however the impossible is defined, are exactly the same kind of thing as possible worlds (both possible and impossible worlds are sets of propositions). So linguistic ersatzism needs some prior distinction between possibility and impossibility. The modal realist says: X is possible iff it X occurs at some world. So he can reduce modal facts to non-modal facts. The linguistic ersatzist can't do that.
"Obviously to describe a world of A-matter and B-matter you need to include statements describing the distribution of A-matter and B-matter in the world. Then in a world where A-matter repels and B-matter attracts, you end up with repulsion in all the places there would have been attraction. That seems like a pretty huge distinction!"
The problem is with the very idea that A-matter and B-matter could swap roles given linguistic ersatzism. Yes, the worlds are different in terms of the distribution of repulsion and attraction. The question is, how do you know that you're talking about a world where A-matter and B-matter have swapped roles, rather than world where the distribution of A-matter and B-matter is different? The difficulty is about how we specify what A-matter and B-matter are.
For what it's worth though, I'm inclined to agree with you that linguistic ersatzism provides enough possible worlds for any practical purpose, so this isn't really a serious problem. If it turns out that, given linguistic ersatzism, we have difficulty dealing with worlds with completely alien properties, I think the linguistic ersatzist should just bite the bullet and insist that such alien properties aren't really possible, contrary to what our intuitions might be.
Kane B "All I would say is that when the platonist says 'numbers exist', he's using 'exist' in the same way as when I say 'tables and chairs exist' or when a theist says 'God exists'."
Indeed, this is quite unhelpful. Numbers are clearly a different category of thing than tables, chairs, and God. Saying that numbers exist in the same way that chairs exist is like saying my emotions are blue in the same way that cerulean paint is blue. Am I saying that my emotions are visible? In the same way, are platonists saying that numbers are tangible objects like chairs? Sadly, that's not what we mean, though that would clarify the issue.
That numbers would continue to do this incomprehensible thing with or without minds is also remarkably uninformative.
"It is true within the possible worlds fiction that all possible worlds exist."
That's true, but what about within each possible world of the possible worlds fiction? Each possible world obviously has a set of things which are true. The question is, within the possible worlds of the possible worlds fiction, are the other possible worlds real or are they like Itchy and Scratchy, a fiction within a fiction? If from within the fiction the other possible worlds are still fictional, then "According to the possible worlds fiction, it is true at every possible world that all possible worlds exist," is not really collapsing fictionalism into realism because it's just talking about a fiction within the fiction.
Surely a fictionalist would imagine possible worlds where fictionalism applies.
"How do you know that you're talking about a world where A-matter and B-matter have swapped roles, rather than world where the distribution of A-matter and B-matter is different?"
So we're essentially constructing two worlds that are the same in every conceivable way, and then asking how linguistic ersatzism can distinguish them. In such a situation, if we decide that linguistic ersatzism cannot distinguish the two worlds then we're really saying that linguistic ersatzism entails the identity of indiscernables for possible worlds.
"I think the linguistic ersatzist should just bite the bullet and insist that such alien properties aren't really possible."
On the contrary, the linguistic ersatzist should insist that indescribable alien properties are possible. If something is indescribable it can only mean that we don't have the linguistic tools to talk about it, but new words can always be invented, and as soon as we invent the necessary words the indescribable alien properties must inevitably become describable, at which point they would have to be called possible by the linguistic ersatzist. So if the linguistic ersatzist is going to make any comment at all about indescribable properties the comment should be that they are possible, or else the linguistic ersatzist must allow things to jump between impossible and possible.
On the other hand, if the so-called alien property is not an actual alien property at all and is in fact pure nonsense, then the reason it cannot be described is because there is nothing to describe. In this case, it's not fair to say that we are talking about an alien property and the real question is: Is a pure nonsense property possible under linguistic ersatzism? This is when the linguistic ersatzist should bite the bullet and insist that pure nonsense isn't really possible.
+Ansatz66 Strictly speaking, I'm not sure I'd say that there are different kinds of existence. Certainly the platonist need not say that. The standard platonist thinks that numbers exist, just like chairs exist, or oceans exist, or electons exist, or whatever (chairs are very different from oceans, but we don't usually say that chairs and oceans have a different kind of existence). As for what kind of thing numbers are - according to the platonist, they're abstract objects. In this respect, they're very much unlike chairs. What exactly does it mean to say that numbers are abstract objects? On this, I can't really help you. I'm not inclined to accept platonism. One of the reasons why I'm not inclined to accept platonism is that the notion of abstract objects has never made much sense to me.
Often, abstract objects are defined in terms of what they're not. They're not spatiotemporal, they're not capable of entering into causal relations, they don't undergo change, etc. You might object that this isn't very informative. I agree.
"That's true, but what about within each possible world of the possible worlds fiction? Each possible world obviously has a set of things which are true. The question is, within the possible worlds of the possible worlds fiction, are the other possible worlds real or are they like Itchy and Scratchy, a fiction within a fiction?"
The former.
Perhaps you could interpret modal fictionalism in the way that you suggest. I don't think this would be a popular option though, because it's straightforwardly inconsistent. On your interpretation, the possible worlds fiction says: all possible worlds exist, and at each possible world, it's a fiction that all possible worlds exist. (Maybe inconsistency isn't such a big deal here, though... it is a fiction, after all.)
"So we're essentially constructing two worlds that are the same in every conceivable way, and then asking how linguistic ersatzism can distinguish them"
The point of the objection is that possibilities outstrip what can be described, so in a certain sense the worlds are identical in terms of what we can conceive about them.
Maybe a different example would be helpful. Consider colours. We might say that it's possible for there to be more colours than there are. It doesn't seem to be logically contradictory for there to be more colours, at any rate. (If you disagree with this, well, just play along for the sake of argument; I'm sure you can substitute a different example). Call one of these alien colours "A" and the other "B". Since A and B don't exist in the actual world, we never have any contact with them. So the only way the linguistic ersatzist can capture them is to describe them. Maybe this can be done. Maybe A is yellow-blue and B is red-green, two colours that, arguably, can't exist in the actual world. Fair enough.
But, presumably, there could be many more colours than this. There could be colours that simply outstrip what we can have the capacity to describe. Colours that we can't imagine, colours that are simply outside of our experience and aren't formed by combinations of colours that we're familiar with. So call two of these colours that we can't describe "C" and "D". Now consider two worlds that are identical except for the distribution of colours. In one world, all planets are C and stars are D, in the other, all planets are D and all stars are C.
The objection is that these situations are possible, and they are different possibilities, but the linguistic ersatzist can't distinguish them. Sure, she can say of one world "all planets are C and all stars are D". But "C" and "D" are just placeholders. The linguistic ersatzist needs to give an actual description of these colours in order to distinguish the worlds, but as noted, these are among the colours that outstrip what we can describe. The placeholders are the best she can do.
"On the contrary, the linguistic ersatzist should insist that indescribable alien properties are possible"
That would just be to give up linguistic ersatzism. To be possible, for the linguistic ersatzist, *just is* to be described within a set of maximal consistent propositions. So lingistic ersatzists certainly can't say that *indescribable* alien properties are possible.
"and as soon as we invent the necessary words the indescribable alien properties must inevitably become describable"
It's not really a matter of what words we have. I didn't get into this in the video, but linguistic ersatzists don't usually take the set of propositions to be English. Anyway, propositions are meanings of sentences, hence often taken to be independent of any language. "Snow is white" and "Schnee ist weiss" both have the same meaning, i.e. they both express the same proposition.
Kane B "One of the reasons why I'm not inclined to accept platonism is that the notion of abstract objects has never made much sense to me."
Surely one need only talk to a platonist and discover what they think they mean by the existence of abstract objects. Doing so seems the least we should do before passing judgement on that philosophy. The principle of charity demands that we not reject a philosophy until we understand it.
I can interpret platonism in a way that makes sense to me. Since an abstract object obviously cannot be tangible in the way that a chair is tangible, an abstract object cannot fully exist in the way that a chair would be said to exist. In this situation, I think the only way to make sense of platonism is to assume that we aren't using the word "exists" in the same sense for abstract objects as they would for chairs. An abstract object could just mean an idea, and to say that an abstract object exists is just to say that it is an idea that someone could potentially have.
"I don't think this would be a popular option though, because it's straightforwardly inconsistent."
The only way we can have an inconsistency is if there is a contradiction within a particular world. When I am constructing my possible worlds fiction, I am absolutely free to assign any truth value to any proposition so long as I do not imply a contradiction, and saying that possible worlds are fictional does not imply a contradiction. Having every world agree that possible worlds are fiction _especially_ does not imply a contradiction.
"On your interpretation, the possible worlds fiction says: all possible worlds exist, and at each possible world, it's a fiction that all possible worlds exist."
I guess that the contradiction we are trying for is that the fiction of our world is inconsistent with the truth in the other possible worlds. That's strange since no one ever expects fiction to be consistent with truth, especially across multiple possible worlds.
"Propositions are meanings of sentences, hence often taken to be independent of any language."
Good point. I see I was confused on that issue. The talk of alien properties made me think that the properties were indescribable due to being alien to our language, but to be indescribable by language-independent propositions is another thing entirely.
"There could be colours that simply outstrip what we can have the capacity to describe."
Since we're being language-independent, we can't use the limits of English to define our capacity to describe things. Those colors may be alien to us, but we ought to be allowed to use a language that would be used by the possible people who can see those colors.
"To be possible, for the linguistic ersatzist, just is to be described within a set of maximal consistent propositions."
Since I now see that the propositions of linguistic ersatzism are language independent, in order to show that there are possibilities beyond the possibilities of linguistic ersatzism we need to show that some possibility cannot be expressed in _any_ language, no matter how alien that language might be.
This seems very challenging, and neither the matter examples nor the color examples seem to clearly establish this point.
+Ansatz66 It's not that I'm unfamiliar with platonism. I have a long video that examines platonism in some detail: ua-cam.com/video/YxgH5ykGwdQ/v-deo.html Re your suggestion, ideas in the mind are fine. That makes sense. But that's not platonism. A crucial elemnt of the platonist account is that mathematical objects are mind-independent.
"The only way we can have an inconsistency is if there is a contradiction within a particular world."
I disagree. Suppose that in one world, "necessarily all swans are blue" is true. Suppose that in another world, "necessarily all swans are blue" is false. In this case, there's no contradiction *within* any particular world, but given how possible worlds discourse works, this is contradictory. The truth in the first world entails that all swans are blue at all worlds at which there are a swans; the truth in the second world entails that in some worlds in which there are swans, some swans are not blue. In other words, in the worlds containing swans, it both is and is not the case that all swans are blue.
The problem with your version of fictionalism is that the fiction says both that all possible worlds exist, but also no possible worlds exist except the possible world that we happen to be talking about at the time (because, at each possible world, every other possible world is merely fictional). That's inconsistent. As I said though, maybe that's not really a problem; maybe the inconsistency doesn't matter because it's only a fiction.
"we ought to be allowed to use a language that would be used by the possible people who can see those colors."
On linguistic ersatzism, there is no such language though. It's no good appealing to to "possible people" because there are no possible people. The linguistic ersatzist has to construct possible worlds using only the resources available in the actual world (that's why linguistic ersatzism is classed as a form of actualism - possible worlds are constructions out of what actually exists).
"This seems very challenging, and neither the matter examples nor the color examples seem to clearly establish this point.?"
I agree with that. Knockdown refutations are very rare in philosophy. There's always a response to any argument. I doubt anybody could come up with an argument that conclusively shows that linguistic ersatzism fails to capture all the possibilities.