Paradoxes can be hard to resolve, so it can be hard to reason well from them. A nice example is a recent argument that the past isn’t infinite, by Laureano Luna (2011: ‘Reasoning from paradox’, The Reasoner 5(2), 22–23). I shall vary the details. Suppose there’s a place where, once a year, every year, someone says “No previous utterance here was true,” with nothing else ever having been said there. Details can be varied, so long as we would, were the past infinite, have an infinite sequence of similar utterances. Indeed, it’s because we can vary the details that the following contradiction seems to follow from supposing the past to be infinite (rather than from, say, supposing that language need not begin with evident truths).
......Each utterance in that place concerned the past, so it seems that each utterance should be either true—were none of the previous utterances there true—or else false—were at least one of them true. But none of them can be either, on pain of Yablo’s paradox: Were no utterance there true then, via what each said, each would be true (and not true); but were any of them true, then since none of the earlier ones would have been true, its immediate predecessor would also, via what it said, have been true (and not true).
......But even if such sequences of utterances are impossible, the past might be infinite. One possibility is that simply infinite sequences, e.g. the natural numbers, are indefinitely extensible (are Potential Infinite) in the sense that while there’s always a next element, e.g. a bigger number, there’s no complete collection of them all. Standard mathematics assumes that such isn’t the case, but we’ve yet to discover that it isn’t. And if it is, then although we naturally think of past years as stretching back in time forever, the past couldn’t be the whole of such an infinite sequence, and so our infinite sequence of utterances would’ve been impossible too. And yet the past might, even so, be infinite. E.g. there might have been, before the Big Bang, some infinitely slow process, which took an infinite time to complete (and before which there might have been something else, possibly with no beginning); such a process has an infinite duration in the sense that we might go any natural number of years back into it and not reach its beginning, and also in the sense that were it the unit of time, all the time since the Big Bang would be relatively infinitesimal.
......Another possibility is that truth, or descriptive accuracy, is essentially a matter of degree. We might take an utterance of “No previous utterance here was true” to be asserting that none of those previous utterances described the past well enough for it to be classed as true. Yablo’s paradox would then be ruling out every possibility except the possibility that all those utterances described the past fairly well, that they were all fairly true. (Does it seem that they would then have been failing to describe the past well enough to be classed as true? If so, note that the suggestion is that either classification—true or not—would be less accurate than that of fairly true.) So, our contradiction may well have been due to our having used, in effect, a rather artificial language. So we seem to have shown only that either the language of those utterances doesn’t allow such sequences of sentences, or something else (e.g. maybe the past isn’t infinite, or maybe the natural numbers are indefinitely extensible).
Monday, February 07, 2011
Monday, January 31, 2011
Philosophers' Carnivals: Now & Next
Philosophers' Carnivals "showcase the best philosophical posts from a wide range of weblogs," as it says on the carnival's homepage. From today, carnival #120 is at nicomachus.net. And carnival #121 will be here in 3 weeks time, so if you find yourself reading something nicely philosophical, posted between now and then, please consider submitting it, via the online submission form, even if you wrote it yourself: "Don't be shy, we want to hear from you, that's the whole point of this project! Your post doesn't need to be anything earth-shattering - it just needs to be something that other philosophically-minded people might enjoy reading."
......As for what you can submit, there are No Rules, except: "No self-help, mysticism, marketing spam, etc." Of course, marketing spammers are unlikely to have bothered reading as far as this, so telling them not to bother submitting seems pointless. And I wouldn't rule out what some academic philosophers like to call 'mysticism', e.g. Mathematical Platonism, Substance Dualism, Open Theism and so forth (since such is just realistic metaphysics). Nor shall I reject whatever formalized craziness such academics work on instead, of course (since I should be unbiased in my hosting). Indeed, since the number of the carnival will be 121 (which sounds like "one-to-one") there's even some hope for self-helpers (and Continental Philosophers) whose positive thinking has carried them thus far, because insofar as their posts describe how the ideal of the Socratic Dialogue relates to their brand of self-help (or Derrida) I shall look upon them kindly.
......Here's a cautionary tale about rule-following: Many years ago, a port on the east coast was industrializing. To its north and south were two large estates, the country houses of two progressive squires, who built factories and docks in the port, and cheap housing for their workers there. Peasants to the west of the port flocked there, to earn more and to be free from their old-fashioned and relatively oppressive squire. As his peasants deserted his lands, that squire soon found himself with cashflow problems, and eventually he was reduced to opening his mansion to the public. He even built an inhumane zoo in its overgrown grounds; but things got no better. He got more and more depressed. One day he became quite deranged, and smashed up his zoo. Then he climbed onto the back of a huge hippopotamus and rode it towards the port. Now, the two rich squires heard of him crashing through their workers' slums, but they were unable to stop him because he had the law on his side, the law which states that the squire on the hippopotamus is evil to the slums of the squires on the other two sides.
......As for what you can submit, there are No Rules, except: "No self-help, mysticism, marketing spam, etc." Of course, marketing spammers are unlikely to have bothered reading as far as this, so telling them not to bother submitting seems pointless. And I wouldn't rule out what some academic philosophers like to call 'mysticism', e.g. Mathematical Platonism, Substance Dualism, Open Theism and so forth (since such is just realistic metaphysics). Nor shall I reject whatever formalized craziness such academics work on instead, of course (since I should be unbiased in my hosting). Indeed, since the number of the carnival will be 121 (which sounds like "one-to-one") there's even some hope for self-helpers (and Continental Philosophers) whose positive thinking has carried them thus far, because insofar as their posts describe how the ideal of the Socratic Dialogue relates to their brand of self-help (or Derrida) I shall look upon them kindly.
......Here's a cautionary tale about rule-following: Many years ago, a port on the east coast was industrializing. To its north and south were two large estates, the country houses of two progressive squires, who built factories and docks in the port, and cheap housing for their workers there. Peasants to the west of the port flocked there, to earn more and to be free from their old-fashioned and relatively oppressive squire. As his peasants deserted his lands, that squire soon found himself with cashflow problems, and eventually he was reduced to opening his mansion to the public. He even built an inhumane zoo in its overgrown grounds; but things got no better. He got more and more depressed. One day he became quite deranged, and smashed up his zoo. Then he climbed onto the back of a huge hippopotamus and rode it towards the port. Now, the two rich squires heard of him crashing through their workers' slums, but they were unable to stop him because he had the law on his side, the law which states that the squire on the hippopotamus is evil to the slums of the squires on the other two sides.
Tuesday, January 25, 2011
Liars, Divine Liars, and Semantics
Divine Liar arguments aim to show that there’s no omniscient being—that no one knows all that’s true—in the following way. Suppose I say “No omniscient being knows that what I’m now saying is true.” If (as I believe) no one is omniscient, then no omniscient being exists, to know anything. So in that case, what I said was true. What I said was therefore an assertion, whether it was true or not. And if it wasn’t true—if it’s not the case that no omniscient being knows that what I said was true—then some omniscient being knows that what I said was true, despite it not being true, which is impossible (knowledge being of truths). So I asserted a truth; and so either that was a truth that some omniscient being doesn’t know, which is also impossible, or else there’s no such being.
......However, resolutions of the Liar Paradox might show that such arguments are invalid, e.g. according to Daniel J. Hill (2007: ‘The Divine Liar Resurfaces’, The Reasoner 1(5), 11–12) and my earlier article (2008: ‘Liars, Divine Liars and Semantics’, The Reasoner 2(12), 4–5). So, suppose I say “What I’m now saying isn’t true.” If what I said was true then, as I said, what I said wasn’t true. Does it follow that what I said wasn’t true? The paradox is that if so, then since that’s what I seem to have said, I seem to have said something true. The resolution defended earlier by me (2008) takes my utterance to have been meaningless, so that I didn’t really say anything. But we may then wonder how it was that it seemed so clear what my utterance would have meant had it been true. And my Divine Liar utterance was even more obviously meaningful. Another popular resolution would regard my Liar utterance as equivocal, with the word ‘true’ naming many different predicates in Hill’s (2007) Tarskian hierarchy. But formal languages can only be defined via natural language; and my informal Divine Liar utterance wasn’t obviously that equivocal.
......Questions of truth are essentially questions of how well our words are describing the world. So insofar as my Liar utterance wasn’t meaningless, it was asserting that it wasn’t describing itself very well, not well enough for it to have been true. And since it was nothing if not self-contradictory, it certainly wasn’t describing itself very well. But therefore, in view of what it was asserting, it seems to have been describing itself quite well after all. Was it describing itself well enough for it to count as true? I’m reluctant to call it ‘true’ as follows. If it was true because it wasn’t, then it was true and not true, but surely something’s only not some way if it’s not the case that it is. Nor do I want to say that it was neither true nor not true, as that’s just to say that it was not true and also true. Nevertheless, my utterance wasn’t describing itself very well, and was therefore describing itself quite well; so perhaps it was only partially true. If so then calling it either ‘true’ or ‘not true’ would both be inaccurate, would both be only partially true.
......We naturally focus upon whatever truth we can find in what people say, or upon an obvious untruth. And things are usually described accurately enough for some obvious purpose, or not accurately enough. But would it be unrealistic to think of truth (descriptive accuracy) as a matter of degree? The classic example is that of Vann McGee (1991: Truth, Vagueness, and Paradox, Hackett, 217): Since “Harry is bald” is true if and only if Harry is bald, so ‘true’ inherits from ‘bald’ its vagueness. But quite generally, why should we believe that our words are much better defined than our purposes have required them to be? Maybe natural language has a ubiquitous—since usually unobtrusive—vagueness. That would explain why the discovery of a contradiction so naturally triggers an attempt to clarify our terminology. And in particular, the Liar Paradox might be revealing this ordinarily obscure vagueness of ‘true’. That’s because if my Liar utterance was only partially true, then it would follow from what I said only that it was also partially not true, which clearly coheres with it being only partially true. There’s no inconsistency—no more paradox—and it seems that much the same could be said of any Liar sentences.
......And if that is how the Liar Paradox should be resolved, then my Divine Liar utterance would have been only partially true if there is an omniscient being. My Divine Liar argument was therefore fallacious, because arguments should have premises that are unequivocally true enough to count as true under all relevant hypotheses. But if you asked an omniscient being whether my Divine Liar utterance was true, she might say that it wasn’t very true, but that it contained an element of the truth. That would be a more informative—more true and less misleading—answer than a simple ‘yes’ or ‘no’ were this how the Liar Paradox should be resolved.
......Similarly, the best answer to the question “Is this colour blue or not?” could be to say that it’s bluish. Ordinary objects are almost always either blue or not, but colours don’t really divide into those that are blue and those that aren’t. On the two sides of any such line, between the blue and the other colours of some spectrum, would be colours that were indistinguishable. So there’s no such division; and so there’s some colour of which, rather than saying that it’s blue, or that it isn’t, we ought to say that it’s bluish. (Such a colour would look blue against a background of colours that weren’t blue, or if you just wondered whether it belonged to that class of colours, and so postulated it amongst them; cf. what we find paradoxical about the Liar Paradox.)
......However, resolutions of the Liar Paradox might show that such arguments are invalid, e.g. according to Daniel J. Hill (2007: ‘The Divine Liar Resurfaces’, The Reasoner 1(5), 11–12) and my earlier article (2008: ‘Liars, Divine Liars and Semantics’, The Reasoner 2(12), 4–5). So, suppose I say “What I’m now saying isn’t true.” If what I said was true then, as I said, what I said wasn’t true. Does it follow that what I said wasn’t true? The paradox is that if so, then since that’s what I seem to have said, I seem to have said something true. The resolution defended earlier by me (2008) takes my utterance to have been meaningless, so that I didn’t really say anything. But we may then wonder how it was that it seemed so clear what my utterance would have meant had it been true. And my Divine Liar utterance was even more obviously meaningful. Another popular resolution would regard my Liar utterance as equivocal, with the word ‘true’ naming many different predicates in Hill’s (2007) Tarskian hierarchy. But formal languages can only be defined via natural language; and my informal Divine Liar utterance wasn’t obviously that equivocal.
......Questions of truth are essentially questions of how well our words are describing the world. So insofar as my Liar utterance wasn’t meaningless, it was asserting that it wasn’t describing itself very well, not well enough for it to have been true. And since it was nothing if not self-contradictory, it certainly wasn’t describing itself very well. But therefore, in view of what it was asserting, it seems to have been describing itself quite well after all. Was it describing itself well enough for it to count as true? I’m reluctant to call it ‘true’ as follows. If it was true because it wasn’t, then it was true and not true, but surely something’s only not some way if it’s not the case that it is. Nor do I want to say that it was neither true nor not true, as that’s just to say that it was not true and also true. Nevertheless, my utterance wasn’t describing itself very well, and was therefore describing itself quite well; so perhaps it was only partially true. If so then calling it either ‘true’ or ‘not true’ would both be inaccurate, would both be only partially true.
......We naturally focus upon whatever truth we can find in what people say, or upon an obvious untruth. And things are usually described accurately enough for some obvious purpose, or not accurately enough. But would it be unrealistic to think of truth (descriptive accuracy) as a matter of degree? The classic example is that of Vann McGee (1991: Truth, Vagueness, and Paradox, Hackett, 217): Since “Harry is bald” is true if and only if Harry is bald, so ‘true’ inherits from ‘bald’ its vagueness. But quite generally, why should we believe that our words are much better defined than our purposes have required them to be? Maybe natural language has a ubiquitous—since usually unobtrusive—vagueness. That would explain why the discovery of a contradiction so naturally triggers an attempt to clarify our terminology. And in particular, the Liar Paradox might be revealing this ordinarily obscure vagueness of ‘true’. That’s because if my Liar utterance was only partially true, then it would follow from what I said only that it was also partially not true, which clearly coheres with it being only partially true. There’s no inconsistency—no more paradox—and it seems that much the same could be said of any Liar sentences.
......And if that is how the Liar Paradox should be resolved, then my Divine Liar utterance would have been only partially true if there is an omniscient being. My Divine Liar argument was therefore fallacious, because arguments should have premises that are unequivocally true enough to count as true under all relevant hypotheses. But if you asked an omniscient being whether my Divine Liar utterance was true, she might say that it wasn’t very true, but that it contained an element of the truth. That would be a more informative—more true and less misleading—answer than a simple ‘yes’ or ‘no’ were this how the Liar Paradox should be resolved.
......Similarly, the best answer to the question “Is this colour blue or not?” could be to say that it’s bluish. Ordinary objects are almost always either blue or not, but colours don’t really divide into those that are blue and those that aren’t. On the two sides of any such line, between the blue and the other colours of some spectrum, would be colours that were indistinguishable. So there’s no such division; and so there’s some colour of which, rather than saying that it’s blue, or that it isn’t, we ought to say that it’s bluish. (Such a colour would look blue against a background of colours that weren’t blue, or if you just wondered whether it belonged to that class of colours, and so postulated it amongst them; cf. what we find paradoxical about the Liar Paradox.)
Saturday, January 01, 2011
Liars Are Fairly True
Suppose I say “what I’m saying isn’t true.” If what I said was true, then as I said, what I said wasn’t true. Does it follow that my words weren’t true? The famous paradox is that if so, then since that’s what I seem to have said, I seem to have said something true. A fairly popular resolution takes my words to have been meaningless, so that I didn’t say anything. But if my words had been meaningless, you could hardly have known what they would have meant had they been true. Is our ordinary conception of truth shown by such Liar-style sentences to be deficient? Let’s see why not.
......To begin with, such sentences are in some ways like Truth-teller-style sentences. If I said “what I’m saying is true,” for example, what would I be saying? Not much. Questions of truth are essentially questions of how well our words describe the world, and “this is a good description” isn’t much of a description. Still, it might not be too bad a self-description, precisely because there isn’t much to describe. If someone saying “what I’m saying is true” intended to be speaking the truth, should we deny that she was telling the truth? It may be hard to say, but therefore it might be that such sentences are not so much vacuous as vague. Since “what I’m saying isn’t true” also addresses nothing but its own descriptive power, might it also be, in its own way, rather vague? Consider the following analogy.
......If I said of some colour, “I wouldn’t say that it’s blue,” I might not be saying that it wasn’t blue, because colours don’t divide into those that are blue and those that aren’t. To see that, consider a spectrum: On the two sides of any such line, between the blue and the other colours, there would be colours that were indistinguishable. So there’s no such division; so there’s some colour of which, rather than saying it was blue, or that it wasn’t, I’d prefer to say, more precisely, that it was bluish but not very blue. (Since the perception of colour is subjective, you might say it was blue, or that it wasn’t.) Our perception of colour is also context-sensitive, e.g. it’s affected by surrounding colours, and by our preconceptions. So if I wondered if our colour really was blue, I might thereby see it as not blue, while if I then wondered if it was therefore not blue, it might seem pretty blue (even to me).
......And similarly, it’s when “what I’m saying isn’t true” has been thought of as definitely not true that it seems most clearly to be true. More precisely, while those words aren’t giving us a very good description of their own meaning—they’re self-contradictory—we therefore have a description that isn’t too bad, insofar as it’s saying that it’s not a very good description. In short, they’re rather nonsensical (and false), but therefore fairly true (and false). And that’s basically how Liar-style sentences are compatible with our ordinary conception of truth. We need a bit more clarification, but it should soon become clear that while we can always be more precise, there’s no threat to truth here.
......What is truth, if not a sufficiently accurate description? Usually we describe things accurately enough for some obvious purpose, or else we don’t, so we tend to assume that truth is black-or-white. But it’s really a matter of degree, in a context-sensitive way. E.g. the table at which I’m writing this is flat enough for that purpose, so “this table is flat” is true enough, but might be false were I writing about geometry. And in general, our words tend not to be much better defined than our purposes have required them to be. So natural language has a ubiquitous—since ordinarily unobtrusive—vagueness (whence the way to resolve paradoxes, and uncover other fallacies, usually involves clarifying some terms). Of course, the words of “what I’m saying isn’t true” have clear enough meanings, so there’s no simple equivocation to discover. But it should help us to resolve the paradox if we don’t demand anything too unrealistic. (Similarly, we shouldn’t demand that colours be either blue or else not blue.)
......Liar-style sentences present themselves as misrepresenting themselves, so their meaning is self-undermining. And they can be read (or heard) in two basic ways—each a necessary part of the other’s context—because their meaning self-undermines in a loopy sort of way. Insofar as Liar-style sentences are true they’re also false, and they need concern nothing but their own truth, so they can certainly be read as nonsensical. But they’re not just senseless, and hence not at all true, because insofar as they’re not true they’re easily read as true. So they also have that sense. But they can’t be nothing but partly true and hence partly false, because that would leave nothing for them to be true or false about.
......This resolution—that Liar-style sentences are fairly true, in that loopy way (they’re fairly true because they’re rather nonsensical, and they’re rather nonsensical because insofar as they’re true they’re also false)—is a strengthened version of the resolution that takes them to be nonsensical. So for those who believe that an omniscient being is logically possible, it allows a similar reply to Divine-Liar-style sentences. E.g. the problem with “no omniscient being knows this” is that it can’t be true if there’s an omniscient being, but if it isn’t true then, since no one could then know it, it would seem to be true. My new reply is that if it’s only fairly true (in this loopy way) then no epistemically perfect being would have to know it, except to know it for what it is. And note that “no omniscient being knows any of this” is simply false, e.g. such a being would know those words. (Similarly, “what I’m saying isn’t at all true” is fairly false.)
......To begin with, such sentences are in some ways like Truth-teller-style sentences. If I said “what I’m saying is true,” for example, what would I be saying? Not much. Questions of truth are essentially questions of how well our words describe the world, and “this is a good description” isn’t much of a description. Still, it might not be too bad a self-description, precisely because there isn’t much to describe. If someone saying “what I’m saying is true” intended to be speaking the truth, should we deny that she was telling the truth? It may be hard to say, but therefore it might be that such sentences are not so much vacuous as vague. Since “what I’m saying isn’t true” also addresses nothing but its own descriptive power, might it also be, in its own way, rather vague? Consider the following analogy.
......If I said of some colour, “I wouldn’t say that it’s blue,” I might not be saying that it wasn’t blue, because colours don’t divide into those that are blue and those that aren’t. To see that, consider a spectrum: On the two sides of any such line, between the blue and the other colours, there would be colours that were indistinguishable. So there’s no such division; so there’s some colour of which, rather than saying it was blue, or that it wasn’t, I’d prefer to say, more precisely, that it was bluish but not very blue. (Since the perception of colour is subjective, you might say it was blue, or that it wasn’t.) Our perception of colour is also context-sensitive, e.g. it’s affected by surrounding colours, and by our preconceptions. So if I wondered if our colour really was blue, I might thereby see it as not blue, while if I then wondered if it was therefore not blue, it might seem pretty blue (even to me).
......And similarly, it’s when “what I’m saying isn’t true” has been thought of as definitely not true that it seems most clearly to be true. More precisely, while those words aren’t giving us a very good description of their own meaning—they’re self-contradictory—we therefore have a description that isn’t too bad, insofar as it’s saying that it’s not a very good description. In short, they’re rather nonsensical (and false), but therefore fairly true (and false). And that’s basically how Liar-style sentences are compatible with our ordinary conception of truth. We need a bit more clarification, but it should soon become clear that while we can always be more precise, there’s no threat to truth here.
......What is truth, if not a sufficiently accurate description? Usually we describe things accurately enough for some obvious purpose, or else we don’t, so we tend to assume that truth is black-or-white. But it’s really a matter of degree, in a context-sensitive way. E.g. the table at which I’m writing this is flat enough for that purpose, so “this table is flat” is true enough, but might be false were I writing about geometry. And in general, our words tend not to be much better defined than our purposes have required them to be. So natural language has a ubiquitous—since ordinarily unobtrusive—vagueness (whence the way to resolve paradoxes, and uncover other fallacies, usually involves clarifying some terms). Of course, the words of “what I’m saying isn’t true” have clear enough meanings, so there’s no simple equivocation to discover. But it should help us to resolve the paradox if we don’t demand anything too unrealistic. (Similarly, we shouldn’t demand that colours be either blue or else not blue.)
......Liar-style sentences present themselves as misrepresenting themselves, so their meaning is self-undermining. And they can be read (or heard) in two basic ways—each a necessary part of the other’s context—because their meaning self-undermines in a loopy sort of way. Insofar as Liar-style sentences are true they’re also false, and they need concern nothing but their own truth, so they can certainly be read as nonsensical. But they’re not just senseless, and hence not at all true, because insofar as they’re not true they’re easily read as true. So they also have that sense. But they can’t be nothing but partly true and hence partly false, because that would leave nothing for them to be true or false about.
......This resolution—that Liar-style sentences are fairly true, in that loopy way (they’re fairly true because they’re rather nonsensical, and they’re rather nonsensical because insofar as they’re true they’re also false)—is a strengthened version of the resolution that takes them to be nonsensical. So for those who believe that an omniscient being is logically possible, it allows a similar reply to Divine-Liar-style sentences. E.g. the problem with “no omniscient being knows this” is that it can’t be true if there’s an omniscient being, but if it isn’t true then, since no one could then know it, it would seem to be true. My new reply is that if it’s only fairly true (in this loopy way) then no epistemically perfect being would have to know it, except to know it for what it is. And note that “no omniscient being knows any of this” is simply false, e.g. such a being would know those words. (Similarly, “what I’m saying isn’t at all true” is fairly false.)
Friday, December 17, 2010
Omniscience Again cont.
This is the last of 17 posts, which are collectively Eternity, etc.
......There is something counter-intuitive about the suggestion of the previous post, of course (even on the modern view of arithmetic). If B is the biggest Beth that has been constructed, then my suggestion denies that 2-to-the-power-of-B exists, where 2-to-the-power-of-B is the cardinality of P(X) when X has cardinality B. Were there no such B, my suggestion would deny that the union of the existing sets has an actual cardinality, on the modern view of the natural numbers (on the older view, it would deny the existence of M + 1, where M is the biggest natural number divinely constructed). Either way, my suggestion is effectively that there are true statements that God did not know but which were bound to be true and which, if we could come to know them, we would most naturally say had always been true. Intuitively, that seems to fall short of divine omniscience.
......Nevertheless, we know from section III that what can seem, with hindsight, to have been timeless truths may not have been. And according to section VII it is logically, not just physiologically, impossible for anyone to say or know all such things. Such statements therefore belong to an indefinitely extensible totality. Would it therefore be more accurate to talk of possible statements here? Maybe not [i], but it’s certainly logically possible that our intuited shortfall is due to our being dependent creatures. For us, even physics is immutable, but God is certainly the ground of metaphysical possibility. And He may well be the ground of all meaning and value. So the counter-intuitiveness of divinely created mathematics may prove, upon reflection, to be no more conclusive than the counter-intuitiveness of Divine Command Metaethics [ii]. After all, my suggestion does not deny that, in the time we took to think of 2-to-the-power-of-B, God had already constructed it [iii].
......So, to recap, God’s omnipotence conflicts with His timelessness, according to section VII, unless we deny arithmetical Realism, or deviate further than Presentism does from standard logic. And under Presentism, even such an omnipotent God could be necessarily omniscient. So what follows from God being necessarily omniscient—and our freedom being libertarian—is primarily disjunctive. Either God has timeless knowledge of the future—if that does cohere with our freedom being libertarian—but Realist arithmetic is paradoxical, or Realist arithmetic is divinely constructed and time is Presentist, or some other option. So even if they regard God as necessarily omniscient, Perfect Being Theists who take a libertarian view of free will—and regard the future as (partially) real—should not reject Open Theism.
......Notes:
......[i] Statements are basically possible assertions (see note ii of Eternity), but a possible statement is not necessarily just a statement. Similarly, one might be unable to say something in French, and yet be able to learn (more) French, so that one would be able to be able to say it. It is of course hard to tell how apposite that analogy is, for the language (so to speak) of God’s thoughts.
......[ii] Lois Malcolm, “Divine Commands,” in Gilbert Meilaender & William Werpehowski (eds.), The Oxford Handbook of Theological Ethics (Oxford Univ. Press, 2005), pp. 112–29.
......[iii] Suppose (see note v of Possible Worlds) that a God who could change had made our 4-dimensional world in an instant. Then some biggest Beth, say B, would be known by Him at all (of our) times. But then we might use “2-to-the-power-of-B” as a definite description of a Beth that He does not know, at any (such) time, which hardly coheres with His being the greatest conceivable being. By contrast, a Presentist God would most plausibly be learning arithmetic too quickly for us to describe any such number.
......There is something counter-intuitive about the suggestion of the previous post, of course (even on the modern view of arithmetic). If B is the biggest Beth that has been constructed, then my suggestion denies that 2-to-the-power-of-B exists, where 2-to-the-power-of-B is the cardinality of P(X) when X has cardinality B. Were there no such B, my suggestion would deny that the union of the existing sets has an actual cardinality, on the modern view of the natural numbers (on the older view, it would deny the existence of M + 1, where M is the biggest natural number divinely constructed). Either way, my suggestion is effectively that there are true statements that God did not know but which were bound to be true and which, if we could come to know them, we would most naturally say had always been true. Intuitively, that seems to fall short of divine omniscience.
......Nevertheless, we know from section III that what can seem, with hindsight, to have been timeless truths may not have been. And according to section VII it is logically, not just physiologically, impossible for anyone to say or know all such things. Such statements therefore belong to an indefinitely extensible totality. Would it therefore be more accurate to talk of possible statements here? Maybe not [i], but it’s certainly logically possible that our intuited shortfall is due to our being dependent creatures. For us, even physics is immutable, but God is certainly the ground of metaphysical possibility. And He may well be the ground of all meaning and value. So the counter-intuitiveness of divinely created mathematics may prove, upon reflection, to be no more conclusive than the counter-intuitiveness of Divine Command Metaethics [ii]. After all, my suggestion does not deny that, in the time we took to think of 2-to-the-power-of-B, God had already constructed it [iii].
......So, to recap, God’s omnipotence conflicts with His timelessness, according to section VII, unless we deny arithmetical Realism, or deviate further than Presentism does from standard logic. And under Presentism, even such an omnipotent God could be necessarily omniscient. So what follows from God being necessarily omniscient—and our freedom being libertarian—is primarily disjunctive. Either God has timeless knowledge of the future—if that does cohere with our freedom being libertarian—but Realist arithmetic is paradoxical, or Realist arithmetic is divinely constructed and time is Presentist, or some other option. So even if they regard God as necessarily omniscient, Perfect Being Theists who take a libertarian view of free will—and regard the future as (partially) real—should not reject Open Theism.
......Notes:
......[i] Statements are basically possible assertions (see note ii of Eternity), but a possible statement is not necessarily just a statement. Similarly, one might be unable to say something in French, and yet be able to learn (more) French, so that one would be able to be able to say it. It is of course hard to tell how apposite that analogy is, for the language (so to speak) of God’s thoughts.
......[ii] Lois Malcolm, “Divine Commands,” in Gilbert Meilaender & William Werpehowski (eds.), The Oxford Handbook of Theological Ethics (Oxford Univ. Press, 2005), pp. 112–29.
......[iii] Suppose (see note v of Possible Worlds) that a God who could change had made our 4-dimensional world in an instant. Then some biggest Beth, say B, would be known by Him at all (of our) times. But then we might use “2-to-the-power-of-B” as a definite description of a Beth that He does not know, at any (such) time, which hardly coheres with His being the greatest conceivable being. By contrast, a Presentist God would most plausibly be learning arithmetic too quickly for us to describe any such number.
Wednesday, December 15, 2010
Omniscience Again
This is the sixteenth of 17 posts, which are collectively Eternity, etc.
......You may be wondering how, if the Open God is forever acquiring arithmetical knowledge (see previous post), He could ever be omniscient (or how His understanding of His options could ever be perfect). It would not even help us here to think of omniscience in Swinburne’s terms, because however much arithmetic God knows it is logically—indeed, metaphysically—possible for Him to know more (according to section VII); and nor could He know all the interesting Beths (that could ever exist) [i], because the smallest Beth that He did not know would be of some objective interest.
......Nevertheless, such Perfect Being Theists as Augustine and Duns Scotus took the Platonic Forms to be divinely created (in view of God’s omnipotence) [ii], and similarly, Open Theists might take arithmetic to be divinely constructed [iii]. Suppose that arithmetical statements are true or false only when divinely proved or refuted (respectively). That process could not always be instantaneous, according to section VII, and of course, not yet knowing something that is not yet true would not obstruct omniscience. And while most of us think of arithmetic as timeless, by “arithmetic” we ordinarily mean finite arithmetic, and on the modern view such a God could have always known all of that (instantaneously constructed in His primal state). Indeed, He could have always known all the Beths that are not, for us, unimaginably large.
......My suggestion is therefore that God, being epistemically omnipotent, constructs each and every modal consequence of the concept of a thing (which He understands perfectly), and in particular the cardinalities of possible creations (doing so endlessly because such is the nature of that concept). He knows all the Beths that exist. Before He constructs a Beth, it has only a potential existence. And eventually (and arbitrarily quickly) He knows any Beth that could ever exist. And His understanding of such possible Beths is perfect (cf. how we could understand the essence of an arbitrary natural number, even on the older view of arithmetic).
......Notes:
......[i] For a similar suggestion, see Menzel, “God and Mathematical Objects,” pp. 93–4 n. 42.
......[ii] For Augustine, see Sorabji, Time, Creation and the Continuum, p. 252. For Duns Scotus, see Gunton, The Triune Creator, pp. 118–9. For more details, see Copan & Craig, Creation out of Nothing, pp. 173–80.
......[iii] Menzel, “God and Mathematical Objects,” defends such a view, called “theistic constructivism” by Copan & Craig, Creation out of Nothing, p. 191.
......You may be wondering how, if the Open God is forever acquiring arithmetical knowledge (see previous post), He could ever be omniscient (or how His understanding of His options could ever be perfect). It would not even help us here to think of omniscience in Swinburne’s terms, because however much arithmetic God knows it is logically—indeed, metaphysically—possible for Him to know more (according to section VII); and nor could He know all the interesting Beths (that could ever exist) [i], because the smallest Beth that He did not know would be of some objective interest.
......Nevertheless, such Perfect Being Theists as Augustine and Duns Scotus took the Platonic Forms to be divinely created (in view of God’s omnipotence) [ii], and similarly, Open Theists might take arithmetic to be divinely constructed [iii]. Suppose that arithmetical statements are true or false only when divinely proved or refuted (respectively). That process could not always be instantaneous, according to section VII, and of course, not yet knowing something that is not yet true would not obstruct omniscience. And while most of us think of arithmetic as timeless, by “arithmetic” we ordinarily mean finite arithmetic, and on the modern view such a God could have always known all of that (instantaneously constructed in His primal state). Indeed, He could have always known all the Beths that are not, for us, unimaginably large.
......My suggestion is therefore that God, being epistemically omnipotent, constructs each and every modal consequence of the concept of a thing (which He understands perfectly), and in particular the cardinalities of possible creations (doing so endlessly because such is the nature of that concept). He knows all the Beths that exist. Before He constructs a Beth, it has only a potential existence. And eventually (and arbitrarily quickly) He knows any Beth that could ever exist. And His understanding of such possible Beths is perfect (cf. how we could understand the essence of an arbitrary natural number, even on the older view of arithmetic).
......Notes:
......[i] For a similar suggestion, see Menzel, “God and Mathematical Objects,” pp. 93–4 n. 42.
......[ii] For Augustine, see Sorabji, Time, Creation and the Continuum, p. 252. For Duns Scotus, see Gunton, The Triune Creator, pp. 118–9. For more details, see Copan & Craig, Creation out of Nothing, pp. 173–80.
......[iii] Menzel, “God and Mathematical Objects,” defends such a view, called “theistic constructivism” by Copan & Craig, Creation out of Nothing, p. 191.
Monday, December 13, 2010
Cantor’s Paradox again
This is the fifteenth of 17 posts, which are collectively Eternity, etc.
......Because of all those unions (see previous post), our collection is a nested hierarchy of sets, whose cardinalities the Beths are defined to be. And so because our collection is not quasi-spatial, nor are the Beths, collectively. So even on the modern view, cardinal arithmetic is indefinitely extensible [i]. And while that result is of a kind with Cantor’s Paradox [ii], it is the belief that cardinal arithmetic is timeless that makes it paradoxical. The atemporalist faces some tough choices, because the truths known by a timeless God would be collectively quasi-spatial, rather than variable.
......But an everlasting God could acquire arithmetical knowledge endlessly. And Presentist time is merely our natural reification of the possibility of change, not a real dimension. And under Presentist Open Theism, that possibility originates with the greatest conceivable being’s power to change. So such a God would have enough time to know each arithmetical truth, and to know it arbitrarily quickly. Time would then be indefinitely extensible, and absolutely continuous [iii], in the sense that for any duration, and for any Actual Infinite cardinal number (that could ever exist), that duration has more than that many instants (possible instantaneous changes).
......It seems, then, that only a God with the power to change is, for every Actual Infinite cardinal number, able to know all about a possible world of so many things, and hence able to create such a world perfectly freely (with a perfect understanding of His options). So the argument at the end of section VI becomes an argument that God is, since omnipotent, not timeless. And note that the informality of this rather mathematical section does not make that a weak argument. Formal proofs can only prove theorems within axiomatic systems, and since the justification of such axioms is necessarily informal, so informality also suits a more direct argument about metaphysically possible creations.
......Notes:
......[i] For more details, see W. D. Hart, “The Potential Infinite,” Proceedings of the Aristotelian Society 76 (1976): 247–64; Alvin Plantinga & Patrick Grim, “Truth, Omniscience, and Cantorian Arguments: An exchange,” Philosophical Studies 71 (1993): 267–306; Stewart Shapiro & Crispin Wright, “All Things Indefinitely Extensible,” in Agustin Rayo & Gabriel Uzquiano (eds.), Absolute Generality (Clarendon Press, 2006), pp. 255–304; Nicholas Rescher & Patrick Grim, “Plenum Theory,” Noûs 42 (2008): 422–39.
......[ii] For Georg Cantor, sets were consistent Actual Infinite collections. But he thought that all Potential Infinite collections presuppose Actual Infinite collections, much as mathematical variables range over fixed domains. So he thought of collections like that of all the sets (Cantor’s Paradox) or all the cardinal numbers as Actual Infinite but inconsistent. For more details, see Michael Hallett, Cantorian set theory and limitation of size (Clarendon Press, 1984), pp. 24–48. Of course, taking inconsistency on the chin like that is a high a price to pay for Realism (whence the foundation of mainstream mathematics is now an axiomatic set theory). But even if Potential Infinite collections do depend upon something being Actual Infinite, that might be a power (see note iv in Cantor's Paradox) or a length (see following note) rather than a collection.
......[iii] For such continua, see my “To Continue with Continuity,” Metaphysica 6 (2005): 91–109; Philip Ehrlich, “The Absolute Arithmetic Continuum and its Peircean Counterpart,” in Matthew Moore (ed.), New Essays on Peirce’s Mathematical Philosophy (Open Court, forthcoming).
......Because of all those unions (see previous post), our collection is a nested hierarchy of sets, whose cardinalities the Beths are defined to be. And so because our collection is not quasi-spatial, nor are the Beths, collectively. So even on the modern view, cardinal arithmetic is indefinitely extensible [i]. And while that result is of a kind with Cantor’s Paradox [ii], it is the belief that cardinal arithmetic is timeless that makes it paradoxical. The atemporalist faces some tough choices, because the truths known by a timeless God would be collectively quasi-spatial, rather than variable.
......But an everlasting God could acquire arithmetical knowledge endlessly. And Presentist time is merely our natural reification of the possibility of change, not a real dimension. And under Presentist Open Theism, that possibility originates with the greatest conceivable being’s power to change. So such a God would have enough time to know each arithmetical truth, and to know it arbitrarily quickly. Time would then be indefinitely extensible, and absolutely continuous [iii], in the sense that for any duration, and for any Actual Infinite cardinal number (that could ever exist), that duration has more than that many instants (possible instantaneous changes).
......It seems, then, that only a God with the power to change is, for every Actual Infinite cardinal number, able to know all about a possible world of so many things, and hence able to create such a world perfectly freely (with a perfect understanding of His options). So the argument at the end of section VI becomes an argument that God is, since omnipotent, not timeless. And note that the informality of this rather mathematical section does not make that a weak argument. Formal proofs can only prove theorems within axiomatic systems, and since the justification of such axioms is necessarily informal, so informality also suits a more direct argument about metaphysically possible creations.
......Notes:
......[i] For more details, see W. D. Hart, “The Potential Infinite,” Proceedings of the Aristotelian Society 76 (1976): 247–64; Alvin Plantinga & Patrick Grim, “Truth, Omniscience, and Cantorian Arguments: An exchange,” Philosophical Studies 71 (1993): 267–306; Stewart Shapiro & Crispin Wright, “All Things Indefinitely Extensible,” in Agustin Rayo & Gabriel Uzquiano (eds.), Absolute Generality (Clarendon Press, 2006), pp. 255–304; Nicholas Rescher & Patrick Grim, “Plenum Theory,” Noûs 42 (2008): 422–39.
......[ii] For Georg Cantor, sets were consistent Actual Infinite collections. But he thought that all Potential Infinite collections presuppose Actual Infinite collections, much as mathematical variables range over fixed domains. So he thought of collections like that of all the sets (Cantor’s Paradox) or all the cardinal numbers as Actual Infinite but inconsistent. For more details, see Michael Hallett, Cantorian set theory and limitation of size (Clarendon Press, 1984), pp. 24–48. Of course, taking inconsistency on the chin like that is a high a price to pay for Realism (whence the foundation of mainstream mathematics is now an axiomatic set theory). But even if Potential Infinite collections do depend upon something being Actual Infinite, that might be a power (see note iv in Cantor's Paradox) or a length (see following note) rather than a collection.
......[iii] For such continua, see my “To Continue with Continuity,” Metaphysica 6 (2005): 91–109; Philip Ehrlich, “The Absolute Arithmetic Continuum and its Peircean Counterpart,” in Matthew Moore (ed.), New Essays on Peirce’s Mathematical Philosophy (Open Court, forthcoming).
Saturday, December 11, 2010
Cantor’s Paradox cont.
This is the fourteenth of 17 posts, which are collectively Eternity, etc.
......You may be familiar with N (see previous post) from school mathematics. Such informal sets are basically collections that are quasi-spatial, in the sense that their members coexist (insofar as they do exist) altogether. Given any spatial collection—e.g. some ordinary objects in a room—any sub-collection of them is clearly also spatial; and similarly, a definitive property of our informal sets is that every conceivable sub-collection of such a set is itself quasi-spatial, is a subset [i].
......Surprisingly, the modern view (of arithmetic as timeless) offers little support to atemporalism, as follows. To say that two collections have the same cardinality—the same cardinal number of members—is to say that the members of each collection could all be paired off, one-to-one, with those of the other [ii]. And for any set, S, if the collection of all its subsets is also quasi-spatial, then that collection—including (for simplicity) the so-called improper subsets, S and the empty set—is the powerset of S, say P(S). And according to Cantor’s Diagonal Argument [iii], P(S) always has a greater cardinality than S.
......In particular, the cardinality of P(N)—which Peirce called “Beth-1”—is greater than the cardinality of N, which is Beth-0. And the cardinality of P(P(N)) = P-squared(N) is Beth-2, which is greater than Beth-1. And so on; for each natural number n, P-to-the-nth-power(N) has Beth-n members. And the union of N and all those P-to-the-nth-power(N) is the collection of all their members. For each n it contains at least Beth-(n + 1) members. So its cardinality, say Beth-omega [iv], is greater than Beth-n for every n. And if that union is also a set, say U, then by Cantor’s Diagonal Argument, P(U) has an even greater cardinality, Beth-(omega + 1) [v],
......We might expect that union to be a set, because Beth-0 being an Actual Infinite number means that all those Beth-0 sets coexist quasi-spatially (like a row of houses, whose contents therefore coexist similarly). So the next union might be of U and all the P-to-the-nth-power(U). But by continuing in that way, taking powersets and unions as far as is logically possible [vi], we cannot end up with a set because from any set we could have continued further in that way. We have, then, a collection that is not quasi-spatial, being generated by a process that cannot be completed (as a matter of logical necessity).
......Notes:
......[i] By contrast, if the natural numbers are forever growing, according to the rule of add 1 repeatedly, then only those sub-collections that are similarly specified by a finite rule exist in the same kind of way.
......[ii] The natural numbers are finite cardinal numbers. And N has the same infinite cardinality as the subset of just the even numbers because n can be paired with 2n for all natural numbers n. There are, in an obvious sense, more natural numbers than even numbers, but cardinality is fundamental to our number concept; Shapiro, Thinking about Mathematics, pp. 133–8.
......[iii] If S and P(S) had the same cardinality, there would be one-to-one mappings from S onto all of P(S). Let M be one such mapping, and let a subset of S, say D, be specified as follows: For each member of S, if the subset that M maps it to contains it then D does not contain it, and otherwise D does. The problem is that since D differs from every subset that M maps the members of S to, D differs from every subset of S, whereas D is by definition a subset of S. That is, D is contradictory, and so there is no such M, which means that S and P(S) do not have the same cardinality. But for each member of S, say m, P(S) contains {m}, and so the cardinality of P(S) is greater than that of S.
......[iv] Omega is the first ordinal number after the natural numbers. Ordinal numbers generalize counting numbers as such beyond the natural numbers (whence their use indexing the Beths).
......[v] Such ordinal addition corresponds to a rearrangement of the natural numbers, e.g. from their natural order (to which omega corresponds) to 2, 3, ..., 1.
......[vi] We could also take unions of Beth-1 sets, since Beth-1 is Actual Infinite; and similarly, Beth-2 sets, etc.
......You may be familiar with N (see previous post) from school mathematics. Such informal sets are basically collections that are quasi-spatial, in the sense that their members coexist (insofar as they do exist) altogether. Given any spatial collection—e.g. some ordinary objects in a room—any sub-collection of them is clearly also spatial; and similarly, a definitive property of our informal sets is that every conceivable sub-collection of such a set is itself quasi-spatial, is a subset [i].
......Surprisingly, the modern view (of arithmetic as timeless) offers little support to atemporalism, as follows. To say that two collections have the same cardinality—the same cardinal number of members—is to say that the members of each collection could all be paired off, one-to-one, with those of the other [ii]. And for any set, S, if the collection of all its subsets is also quasi-spatial, then that collection—including (for simplicity) the so-called improper subsets, S and the empty set—is the powerset of S, say P(S). And according to Cantor’s Diagonal Argument [iii], P(S) always has a greater cardinality than S.
......In particular, the cardinality of P(N)—which Peirce called “Beth-1”—is greater than the cardinality of N, which is Beth-0. And the cardinality of P(P(N)) = P-squared(N) is Beth-2, which is greater than Beth-1. And so on; for each natural number n, P-to-the-nth-power(N) has Beth-n members. And the union of N and all those P-to-the-nth-power(N) is the collection of all their members. For each n it contains at least Beth-(n + 1) members. So its cardinality, say Beth-omega [iv], is greater than Beth-n for every n. And if that union is also a set, say U, then by Cantor’s Diagonal Argument, P(U) has an even greater cardinality, Beth-(omega + 1) [v],
......We might expect that union to be a set, because Beth-0 being an Actual Infinite number means that all those Beth-0 sets coexist quasi-spatially (like a row of houses, whose contents therefore coexist similarly). So the next union might be of U and all the P-to-the-nth-power(U). But by continuing in that way, taking powersets and unions as far as is logically possible [vi], we cannot end up with a set because from any set we could have continued further in that way. We have, then, a collection that is not quasi-spatial, being generated by a process that cannot be completed (as a matter of logical necessity).
......Notes:
......[i] By contrast, if the natural numbers are forever growing, according to the rule of add 1 repeatedly, then only those sub-collections that are similarly specified by a finite rule exist in the same kind of way.
......[ii] The natural numbers are finite cardinal numbers. And N has the same infinite cardinality as the subset of just the even numbers because n can be paired with 2n for all natural numbers n. There are, in an obvious sense, more natural numbers than even numbers, but cardinality is fundamental to our number concept; Shapiro, Thinking about Mathematics, pp. 133–8.
......[iii] If S and P(S) had the same cardinality, there would be one-to-one mappings from S onto all of P(S). Let M be one such mapping, and let a subset of S, say D, be specified as follows: For each member of S, if the subset that M maps it to contains it then D does not contain it, and otherwise D does. The problem is that since D differs from every subset that M maps the members of S to, D differs from every subset of S, whereas D is by definition a subset of S. That is, D is contradictory, and so there is no such M, which means that S and P(S) do not have the same cardinality. But for each member of S, say m, P(S) contains {m}, and so the cardinality of P(S) is greater than that of S.
......[iv] Omega is the first ordinal number after the natural numbers. Ordinal numbers generalize counting numbers as such beyond the natural numbers (whence their use indexing the Beths).
......[v] Such ordinal addition corresponds to a rearrangement of the natural numbers, e.g. from their natural order (to which omega corresponds) to 2, 3, ..., 1.
......[vi] We could also take unions of Beth-1 sets, since Beth-1 is Actual Infinite; and similarly, Beth-2 sets, etc.
Thursday, December 09, 2010
Cantor's Paradox
This is the thirteenth of 17 posts, which are collectively Eternity, etc.
......This section is rather mathematical, but we can—indeed, should—begin with the simplest numbers, 1, 2, 3, etc. Mainstream mathematics has axiomatic set theory for a foundation, for such reasons as Cantor’s Paradox [i], and pure mathematicians are certainly free to explore any interesting formal possibilities. But we are primarily interested in possibilities insofar as they are (or might be) grounded in the God that is.
......The natural (or counting) numbers are the products of endlessly reiterating the addition of 1, starting with 1. They are clearly instantiated, because you and I are 2 people. Arithmetic is prima facie the science of such elementary metaphysical possibilities as the possibility of two individuals. Such arithmetical Realism may be difficult to justify atheistically [ii], but we may think of the natural numbers as existing amongst God’s thoughts, arising via His epistemic omnipotence from His perfect grasp of the concept of a thing, whence our informal 1, together with a concept associated with His omnipotence, such as possibility, whence informal addition and its endless reiteration. Note that Realist arithmetic can be discovered a priori under Theism because we instantiate the concept of a thing and were created in God’s image (and we might also be divinely inspired) [iii].
......The endless reiteration of the addition of 1 means that the natural numbers are (collectively) infinite. Many mathematicians have taken them to be Potential Infinite, as Aristotle put it [iv], or as J. S. Mill put it, indefinitely extensible. The addition of 1 is a definite process, but the natural numbers would have no fixed extension if the endless reiteration of the addition of 1 led to growth that could not even in principle be completed. But most of us think of arithmetic as timeless, and the modern view of the natural numbers is that they are (collectively) Actual Infinite, existing as an immutably complete collection, N = {1, 2, 3, …}.
......Notes:
......[i] Within an axiomatic set theory, Cantor’s Theorem says only that there is no such set of all such sets. For Cantor’s Paradox, see note iii of Divine Attributes.
......[ii] For some well-known problems, see Stewart Shapiro, Thinking about Mathematics: The philosophy of mathematics (Oxford Univ. Press, 2000), pp. 107–289; George Lakoff & Rafael E. Núñez, Where Mathematics Comes From: How the embodied mind brings mathematics into being (Basic Books, 2000), pp. 342–3.
......[iii] For more details, see Christopher Menzel, “God and Mathematical Objects,” in Russell W. Howell & W. James Bradley (eds.), Mathematics in a Postmodern Age: A Christian perspective (Eerdmans, 2001), pp. 65–97 (especially pp. 92–6).
......[iv] To see what Aristotle meant, consider an everlasting fruit-tree. The tree’s endless production of fruit is the ever-incomplete expression of its power to fruit. The total amount of fruit produced is always finite, but always increasing; it is unlimited—is Potential Infinite—because the tree’s power to fruit remains infinite. For more details, see Copan & Craig, Creation out of Nothing, pp. 200–10; Peter Fletcher, “Infinity,” in Dale Jacquette (ed.), Philosophy of Logic (Elsevier, 2007), pp. 523–85.
......This section is rather mathematical, but we can—indeed, should—begin with the simplest numbers, 1, 2, 3, etc. Mainstream mathematics has axiomatic set theory for a foundation, for such reasons as Cantor’s Paradox [i], and pure mathematicians are certainly free to explore any interesting formal possibilities. But we are primarily interested in possibilities insofar as they are (or might be) grounded in the God that is.
......The natural (or counting) numbers are the products of endlessly reiterating the addition of 1, starting with 1. They are clearly instantiated, because you and I are 2 people. Arithmetic is prima facie the science of such elementary metaphysical possibilities as the possibility of two individuals. Such arithmetical Realism may be difficult to justify atheistically [ii], but we may think of the natural numbers as existing amongst God’s thoughts, arising via His epistemic omnipotence from His perfect grasp of the concept of a thing, whence our informal 1, together with a concept associated with His omnipotence, such as possibility, whence informal addition and its endless reiteration. Note that Realist arithmetic can be discovered a priori under Theism because we instantiate the concept of a thing and were created in God’s image (and we might also be divinely inspired) [iii].
......The endless reiteration of the addition of 1 means that the natural numbers are (collectively) infinite. Many mathematicians have taken them to be Potential Infinite, as Aristotle put it [iv], or as J. S. Mill put it, indefinitely extensible. The addition of 1 is a definite process, but the natural numbers would have no fixed extension if the endless reiteration of the addition of 1 led to growth that could not even in principle be completed. But most of us think of arithmetic as timeless, and the modern view of the natural numbers is that they are (collectively) Actual Infinite, existing as an immutably complete collection, N = {1, 2, 3, …}.
......Notes:
......[i] Within an axiomatic set theory, Cantor’s Theorem says only that there is no such set of all such sets. For Cantor’s Paradox, see note iii of Divine Attributes.
......[ii] For some well-known problems, see Stewart Shapiro, Thinking about Mathematics: The philosophy of mathematics (Oxford Univ. Press, 2000), pp. 107–289; George Lakoff & Rafael E. Núñez, Where Mathematics Comes From: How the embodied mind brings mathematics into being (Basic Books, 2000), pp. 342–3.
......[iii] For more details, see Christopher Menzel, “God and Mathematical Objects,” in Russell W. Howell & W. James Bradley (eds.), Mathematics in a Postmodern Age: A Christian perspective (Eerdmans, 2001), pp. 65–97 (especially pp. 92–6).
......[iv] To see what Aristotle meant, consider an everlasting fruit-tree. The tree’s endless production of fruit is the ever-incomplete expression of its power to fruit. The total amount of fruit produced is always finite, but always increasing; it is unlimited—is Potential Infinite—because the tree’s power to fruit remains infinite. For more details, see Copan & Craig, Creation out of Nothing, pp. 200–10; Peter Fletcher, “Infinity,” in Dale Jacquette (ed.), Philosophy of Logic (Elsevier, 2007), pp. 523–85.
Wednesday, December 08, 2010
English Numbers
Hartley Slater in The Reasoner 4(12), 175–6, tried to show, from the fact that the number of elements in the empty set is zero, that zero is not, as a matter of English grammar, the empty set—and in general, that numbers are not sets—because we don’t say that the number of elements in the empty set is the empty set. But things aren’t quite that simple.
......To begin with, Slater’s example of zero—which is often defined to be the empty set in pure mathematics—was an unfortunate choice, because mathematicians introduced zero relatively recently. Consequently English remains rather ambivalent about its status. There being no elephants in this room, for example, it’s false that there are a number of elephants here. So from it being true that there are zero elephants here, surface grammar might seem to indicate that zero isn’t even a number (a cardinal number). But zero is of course a number (the number of elephants in this room, the number of elements in the empty set).
......For another example, the numbers one, two, three etc. correspond to the positions first, second, third and so forth. And since no sequence has an element before the first one—that’s what ‘first’ means—so, in that ordinary sense, there’s no zeroth element, and so again, surface grammar seems to indicate that zero isn’t a number (an ordinal number). Nonetheless, there’s a more mathematical sense in which whenever an element is indexed by 0, it’s a zeroth element.
......In many mathematics textbooks there’s a Chapter 0, for example, containing the set-theoretic basics. Of course, such chapters don’t amount to much evidence that mathematicians take numbers to be nothing more than sets. Mathematicians make the standard identification of numbers with sets in order to prove theorems from set-theoretic axioms. They are thereby following in the footsteps of those who did geometry by proving theorems from Euclid’s axioms. And surely few if any geometers thought that there was nothing more to space than Euclid’s axioms. Space was rather the obvious space around us, of which Euclid’s axioms were taken to be true (and obvious enough to be the premises of proofs).
......Now, even if the space that we see around us is Euclidean—having been constructed as such by our brains from our sensory input—it’s surely not unlikely that what Aristotle meant by ‘space’ is non-Euclidean. So, similarly, even if our concept of zero comes (for example) from reifying the definitive property of an absence, it doesn’t follow that it’s impossible that Euler’s ‘0’ referred to an empty set. Indeed, the standard empty set can be an urelement—can be anything that has no members (where membership is an axiomatic primitive)—because its job within standard set theory is simply to have no members, and so in that sense (at least) zero can be an empty set.
......But more to the point, Slater’s argument may beg the question. That’s because if ‘the empty set’ was a definite description of zero then we could say that the number of elements in the empty set is the empty set (for all that we wouldn’t usually). After all, we can say that the number of ones in zero is zero. In general, for natural numbers n, the number of ones in n is n. Perhaps it would be more natural for us to say that two twos are four (for example), and hence that the number of twos in four is two. But such equations all follow from the natural numbers—most obviously those greater than 1—being essentially sums of ones, which seem to be some sort of collection, perhaps not unlike sets of points in that, while their elements are in obvious ways identical, they are distinguished in ways that derive from their origins (as positions in space, in the case of points).
......Two twos are four because any two things plus another two things are four things. And in English, there being a number of things of some kind is just there being some things of that kind. So again, surface grammar indicates that numbers—most obviously those greater than 1—are some sort of collection. And we might expect mathematicians to be the experts on what exactly numbers are. So, since mathematicians prove theorems about numbers from set-theoretic axioms, we’ve some evidence that numbers are sets.
......Still, such evidence is compatible with numbers being axiomatic sets only in a rather abstract way (cf. how the integers with addition are an abelian group). Slater’s argument was based on surface grammar, so it was presumably that numbers are not sets in some more obvious sense. So note that collections in the usual, informal sense can be variable, like a stamp collection, or non-variable, like a chess set. A fundamental question in this area is therefore whether mathematicians have discovered that numbers behave like sets—at least to the extent that the natural numbers are, collectively, non-variable—or whether they’ve just tended to assume that (even though we can’t so easily assume that cardinal or ordinal numbers are non-variable, in light of the famous set-theoretic paradoxes).
......Mathematicians don’t prove the standard Axiom of Infinity—which asserts the existence of a set containing one element for each natural number (amongst other axioms giving such sets the properties one would expect of non-variable collections)—but rather prove theorems from that axiom (along with the others), or work from some other foundation. Philosophical arguments are therefore needed, to assess whether the standard axioms are giving us a scientifically adequate description of the natural numbers or not. But arguments based on surface grammar are unlikely to be of much help in this area. After all, they can’t even show zero to be a number. (For a more apposite sort of argument, see my 2003: ‘Infinite Sequences: Finitist Consequence,’ The British Journal for the Philosophy of Science 54, 591–9, and my 2010: ‘Two Envelopes, two paradoxes,’ The Reasoner 4(5), 74–5.)
......To begin with, Slater’s example of zero—which is often defined to be the empty set in pure mathematics—was an unfortunate choice, because mathematicians introduced zero relatively recently. Consequently English remains rather ambivalent about its status. There being no elephants in this room, for example, it’s false that there are a number of elephants here. So from it being true that there are zero elephants here, surface grammar might seem to indicate that zero isn’t even a number (a cardinal number). But zero is of course a number (the number of elephants in this room, the number of elements in the empty set).
......For another example, the numbers one, two, three etc. correspond to the positions first, second, third and so forth. And since no sequence has an element before the first one—that’s what ‘first’ means—so, in that ordinary sense, there’s no zeroth element, and so again, surface grammar seems to indicate that zero isn’t a number (an ordinal number). Nonetheless, there’s a more mathematical sense in which whenever an element is indexed by 0, it’s a zeroth element.
......In many mathematics textbooks there’s a Chapter 0, for example, containing the set-theoretic basics. Of course, such chapters don’t amount to much evidence that mathematicians take numbers to be nothing more than sets. Mathematicians make the standard identification of numbers with sets in order to prove theorems from set-theoretic axioms. They are thereby following in the footsteps of those who did geometry by proving theorems from Euclid’s axioms. And surely few if any geometers thought that there was nothing more to space than Euclid’s axioms. Space was rather the obvious space around us, of which Euclid’s axioms were taken to be true (and obvious enough to be the premises of proofs).
......Now, even if the space that we see around us is Euclidean—having been constructed as such by our brains from our sensory input—it’s surely not unlikely that what Aristotle meant by ‘space’ is non-Euclidean. So, similarly, even if our concept of zero comes (for example) from reifying the definitive property of an absence, it doesn’t follow that it’s impossible that Euler’s ‘0’ referred to an empty set. Indeed, the standard empty set can be an urelement—can be anything that has no members (where membership is an axiomatic primitive)—because its job within standard set theory is simply to have no members, and so in that sense (at least) zero can be an empty set.
......But more to the point, Slater’s argument may beg the question. That’s because if ‘the empty set’ was a definite description of zero then we could say that the number of elements in the empty set is the empty set (for all that we wouldn’t usually). After all, we can say that the number of ones in zero is zero. In general, for natural numbers n, the number of ones in n is n. Perhaps it would be more natural for us to say that two twos are four (for example), and hence that the number of twos in four is two. But such equations all follow from the natural numbers—most obviously those greater than 1—being essentially sums of ones, which seem to be some sort of collection, perhaps not unlike sets of points in that, while their elements are in obvious ways identical, they are distinguished in ways that derive from their origins (as positions in space, in the case of points).
......Two twos are four because any two things plus another two things are four things. And in English, there being a number of things of some kind is just there being some things of that kind. So again, surface grammar indicates that numbers—most obviously those greater than 1—are some sort of collection. And we might expect mathematicians to be the experts on what exactly numbers are. So, since mathematicians prove theorems about numbers from set-theoretic axioms, we’ve some evidence that numbers are sets.
......Still, such evidence is compatible with numbers being axiomatic sets only in a rather abstract way (cf. how the integers with addition are an abelian group). Slater’s argument was based on surface grammar, so it was presumably that numbers are not sets in some more obvious sense. So note that collections in the usual, informal sense can be variable, like a stamp collection, or non-variable, like a chess set. A fundamental question in this area is therefore whether mathematicians have discovered that numbers behave like sets—at least to the extent that the natural numbers are, collectively, non-variable—or whether they’ve just tended to assume that (even though we can’t so easily assume that cardinal or ordinal numbers are non-variable, in light of the famous set-theoretic paradoxes).
......Mathematicians don’t prove the standard Axiom of Infinity—which asserts the existence of a set containing one element for each natural number (amongst other axioms giving such sets the properties one would expect of non-variable collections)—but rather prove theorems from that axiom (along with the others), or work from some other foundation. Philosophical arguments are therefore needed, to assess whether the standard axioms are giving us a scientifically adequate description of the natural numbers or not. But arguments based on surface grammar are unlikely to be of much help in this area. After all, they can’t even show zero to be a number. (For a more apposite sort of argument, see my 2003: ‘Infinite Sequences: Finitist Consequence,’ The British Journal for the Philosophy of Science 54, 591–9, and my 2010: ‘Two Envelopes, two paradoxes,’ The Reasoner 4(5), 74–5.)
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