Monday, July 17, 2006

Possible Alternatives You Can't Possibly Take

Here's another way to illuminate the distinction between content-based and brute modality. The former is merely a matter of identifying alternatives ways for worlds to be. The latter is concerned with whether those ways really had a chance to be actualized.

Imagine yourself wanting to buy a Ford back in the days when you could have "any colour you want, so long as it's black." All the cars are black. But blue cars were still possible, in the sense that a car's being blue is an alternative to its being black. (On this understanding, "possible alternative" is redundant. Possibilities just are alternatives to the way things are.) But it's not an alternative you, as a car-buyer, have access to. It's not an option you can take. So a blue car is not a possibility in this more involved sense.

Of course, that latter sense is a lot narrower than metaphysical possibility, even of the brute sort that I have in mind. The analogy is imperfect. But I hope it is at least suggestive. We can imagine other world-states that are alternatives to this one. That gives us the standard space of possible worlds. But it's a separate question whether they're possibilities that "could have been taken" (by God, or the cosmos, or whatever). We can still ask whether they are really possible, in this more demanding sense.

The question can be reworded using the lump/property picture described in my previous post (but ignore the essentialism stuff). Each alternative is a property. But, we may think, that by itself is a merely ontological fact: these abstract states exist. One of them is actually instantiated by the world-lump. But what is the modal status of the other world-properties? They're alternative properties to the one that's actually instantiated, but are they ones that "could have been taken", that really could have been instantiated by the lump? (It probably isn't fair to make the word "really" do so much work here. Unfortunately, I can't think of any better alternatives...)

Some questions:
1) Am I making any sense here? Are there any clearer ways to get at this "brute modal" notion?
2) Is the notion itself fully coherent?
3) Does it correspond to reality? (Is this brute modal status held by some events but not others, say?)
4) Can we establish either way whether all possible worlds are "really possible" in this sense?
5) Are there any other questions I should be asking here?



  1. I might be way off track here, but isn't what you're getting at that there are several senses of possibility, and that they aren't all necessary co-extensional?

    So, in your example, its logically possible to buy a blue car, but not physically possible. Likewise, I might say that its legally possible for me to get pregnant, but biologically impossible (I'm male!).

    As to possible worlds, aren't you suggesting that some logical possibilities are physically impossible? (or similar) To take another example, perhaps its logically possible that no life developed anywhere in the cosmos (there's no contradiction involved there), but nonetheless perhaps it's physically impossible (given, say, some assumptions about the length of time and probabilities of random impacts creating life - thats probably invalid, but you get the idea).


  2. You're certainly right that we can identify narrower (e.g. physical) and broader (e.g. logical) restrictions on possibility. But that's not really what I was trying to get at here. In both those cases, you start with certain content restrictions and define what's possible relative to those. But I'm wanting to get at the idea of a completely different way of characterising modal spaces: one that begins with the modal status ("it really could have happened!"), and at least initially leaves it an open question what the breadth of content restrictions comes to. (Did the initial conditions or the laws of nature ever really have a chance to be different?)

    Those links should give a bit more background, but do let me know if it remains unclear. (Half the difficulty is that I'm not entirely certain myself whether I've actually got a coherent notion in mind here!)

  3. I've thought about this but unfortunately can't offer help. It seems there is a notion "in-between" nomological possibility as it's usually construed and full metaphysical possibility. In thinking about foundations of physics, I've wondered if there a space of possibility which our universe had the needed quantum "propensities" to produce. Anyway, I havent' gotten any farther than that.

  4. It seems to depend on what your surounding assumptions are - then those surrounding together with the statement give a sort of "imposibility factor".

  5. Genius, the notion I have in mind is partly distinguished in virtue of being not merely "relative" or contextual in that way. While content-based notions of possibility are concerned with what's consistent relative to salient background conditions (or what we "hold fixed"), brute modality is instead concerned with what's possible, period. Not relative to this or that assumption. But just straight possible. The world could have turned out that way.

    Steve, there's definitely an interesting notion in the vicinity of what you're talking about (say, possibility relative to natural laws which share the general form of ours, but with different physical constants, or something, right?), but that still sounds like a content-based approach, so not exactly what I have in mind here.

    (Perhaps the difficulty I'm having in finding others with an intuitive grip on this notion is evidence that I don't truly have anything in mind at all? A worry...)

  6. I think I understand where you are coming from, Richard; but I also think that if you subject your intuitions to some more scrutiny you'll discover that they don't bear a veridical correspondence to the nature of possibility.

    You seem to want what we might call "possibility simpliciter", but that's (prima facie, at least) not coherent. You speak of "content-based" notions of possibility, which are "concerned with what's consistent relative to salient background conditions" and contrast this with what you call brute possibility.

    But here's the thing. All it is to make a possibility claim is (as you know) to make a claim about how the world might have been or might be with reference to some fixed some body of facts (e.g. physical or logical law). Possibility simpliciter, that is, possibility without reference to some set of facts, would be about as coherent as a two-place predicate with one subject ("The quick brown fox jumps over.")

    Maybe you're just trying to hash out a brand of possibility which holds fixed some heretofore unconsidered background of facts?

    Also, I get a sense that determinism might be coming into play in your thinking; is it? Things that are possible holding fixed the laws of nature may well be impossible when we include the complete state of the world at an instant in the set of facts we hold fixed. But there's nothing too difficult about that.

  7. "All it is to make a possibility claim is (as you know) to make a claim about how the world might have been or might be with reference to some fixed some body of facts"

    But that's exactly what I'm questioning.

  8. The discussion reaches a bit of an impasse at this point because as I said, my impression is that the claim that possibility can be understood simpliciter--or without reference to any set of facts with which a putative possibility is compossible--is about as coherent as the claim that biological species are actually identical with celestial bodies, or that a two-place predicate can express a proposition with only a single subject.

    In any case, the burden of proof is on you to provide a coherent alternative account of possibility.

  9. I must say I am with Will here. The more I think about your idea of "brute modality" the less I understand what it is supposed to be. To just say "I'm asking whether p is really possible!" is not enough, no matter how much stress you but on the "really". In ordinary situations we always evaluate possibility with respect to some fixed criteria. "Possibility" seems always to mean "compatibility with X", with X depending on the context (logic, physics, initial conditions, etc.) So if you want to have a brute modality you are using "possible" in a wholly different sense, which you ought to define first.

    One of the reasons I am skeptical is that I don't see any way you could possibly find answers to questions like "could the universe have been different?" in your sense. It looks to me you have invented a notion of possibility that (if accepted) brings automatically with it a number of questions of this sort that we have no criteria at all to answer (because you have cut yourself from all criteria) and the answers to those questions would have to be "brute modal facts" that (unlike brute "factual facts", if you pardon the solecism) we have no way of discovering. Isn't it a large price to pay for the privilege of enlarging our range of modal concepts?

  10. Richard –

    do you mean worlds where

    A) There are outright contradictions (i.e. contradictions so tightly defined that there is no conceivable way around them)

    As compared to those hypothetical where
    B) It isn’t tightly defined enough to know it has or doesn’t have fundamental contradictions.
    C) There are no contradictions.

    Ie all relevant facts being within the hypothetical itself.

    (I presume almost every hypothetical is a B unless A or B are “by definition”…)


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