• frank
    2.3k
    Modal rationalism is any view that answers the title question by pointing to a priori knowledge. (conceivability or essence).

    Modal empiricism claims a posteriori sources for modal knowledge.

    And then there are hybrid theories, at least one of which claims that a priori and a posteriori knowledge are so intertwined that they're practically indistinguishable.

    What's your view?
  • Terrapin Station
    7.8k
    Depends on the claim in question.

    "It's possible for my car to be parked on Main Street" is empirical.

    "It's necessary that every existent has a location (or set of locations)" is a priori.
  • frank
    2.3k
    Ok. I propose a micro-debate in which I take modal rationalism against your hybrid view. Ok?
  • Terrapin Station
    7.8k


    Okay. So how would you argue that "It's possible for my car to be parked on Main Street" would be a priori?
  • frank
    2.3k
    Okay. So how would you argue that "It's possible for my car to be parked on Main Street" would be a priori?Terrapin Station

    There are three kinds of possibility for us to consider: physical possibility (what is possible given the natural laws we know), logical possibility (a statement of which does not entail a contradiction), and metaphysical possibility (what could be true given different natural laws or some sort of divinity).

    I'll be arguing that the metaphysical possibility of your car being on Main St can be known a priori.

    Are you still opposing?
  • Terrapin Station
    7.8k
    Are you still opposing?frank

    Yes. For it to be possible, we have to know that there even is a Main Street first off.

    Without getting into a big discussion re if there's a different between "physical" and "metaphysical" possibility, we can just say, by the way, that "It's possible that my car is parked on Main Street" is a modal statement about where my car might be parked given the city it's parked in, as the city is now, etc.
  • frank
    2.3k
    Modal knowledge is only about possibility and necessity. Knowing whether there is a Main St is not modal knowledge.
  • Terrapin Station
    7.8k


    Right. "It's possible that my car is parked on Main Street, given the city it's parked in, as the city is now, etc."

    There's no way to know that without knowing something about the city it's parked in, as the city is now, and that can't be known a priori.
  • frank
    2.3k
    There's no way to know that without knowing something about the city it's parked in, as the city is now, and that can't be known a priori.Terrapin Station

    I don't dispute that one can't know real cities a priori. So I'm afraid we're in agreement.

    I will present an argument opposing modal rationalism involving whether Hesperus could have failed to be Phosphorus.

    I'm drawing on Chalmer's essay: Does conceivability entail possibility?
  • Terrapin Station
    7.8k


    Unsurprisingly if one knows much about my views, I see "conceivability" as primarily telling us about an individual's psychology, knowledge, biases, etc. People often say that "x is conceivable" where I find the idea of it being conceivable very dubious, at least without basically fantasizing in a manner that leaves out all sorts of details.

    So I don't at all think that conceivability entails possibility.

    Re Chalmers paper, where he describes a typical sort of argument, a la:

    "Many arguments in these domains first seek to establish an epistemic gap between two phenomena (e.g. that we can know or conceive of one without the other), argue from there to a modal gap (e.g. that it is possible that one could exist without the other), and step from there to a metaphysical gap (e.g. that one is not reducible to the other),"

    I actually see the biggest gaffe there as the third step. The fact that it's possible that A could exist without B does not at all imply that A is not reducible to B in the actual world.
  • frank
    2.3k
    Chalmers was just explaining a common approach to reduction.

    But I realize now that Kripke is a form of modal rationalism involving deduction from essence.

    For modal empiricism, l have to present modalism, which is along the lines of what you were saying, but you have to bomb possible world semantics first in order to take that ground.
  • frank
    2.3k
    A super villain moved an orphanage to a location directly on top of railroad tracks and barred the doors and windows from the outside.

    Superman, alerted that a train was about to crash into an orphanage, zoomed up and landed on the front of the locomotive. He pushed hard against the train and it slowed down and stopped just in tume to save the kids.

    This scenario is physically impossible. Pushing against the train while attached to it wouldnt have any effect.

    P is that Superman stopped the train in this manner.

    P is true at a physically impossible world.

    By virtue of this, we know P is also true at a metaphysically and logically impossible world.

    True?
  • I like sushi
    280
    It’s a false dichotomy. That’s my view. Also the question of what “knowledge” is needs to be addressed too.
  • Echarmion
    303
    P is that Superman stopped the train in this manner.

    P is true at a physically impossible world.

    By virtue of this, we know P is also true at a metaphysically and logically impossible world.

    True?
    frank

    Isn't it logically and metaphysically possible for the laws of physics to be different from what they are?

    Concerning modal knowledge, it seems similar to the problem of induction. In order to make alethic modal statements based on a posteriori sources, you need to go from specific examples to general rules. So you are using an inductive process.
  • frank
    2.3k
    Isn't it logically and metaphysically possible for the laws of physics to be different from what they are?Echarmion

    Yes. P is true at some logically and metaphysically possible worlds. It's also true at some L and M impossible worlds. The point being: we might imagine that possible world semantics is reducing modality to something non-modal, but it isn't. It's an unnecessary distraction. Modal distinctions are just as primitive in distinguishing possible from impossible worlds as they are in sorting out small scale events, so we can dispense with possible world semantics.

    Concerning modal knowledge, it seems similar to the problem of induction. In order to make alethic modal statements based on a posteriori sources, you need to go from specific examples to general rules. So you are using an inductive process.Echarmion

    Good point. We probably won't be able to claim that knowledge of physical possibility is ever entirely empirical. But the problem of induction doesn't have a rational solution either, so it's a burden to both sides.
  • Arkady
    761

    In case you're interested and haven't seen it, the SEP has an article on this topic.

    https://plato.stanford.edu/entries/modality-epistemology/
  • Terrapin Station
    7.8k
    By virtue of this, we know P is also true at a metaphysically and logically impossible world.frank

    I've never really been convinced that the physical/metaphysical/logical distinction with respect to modality makes much sense.

    And "true in an impossible world" seems wonky to me, too. We fantasize about stuff like Superman pushing against the train simply by ignoring (and or being ignorant of) a lot of details and facts. We make vague analogies to experience and don't worry about the details.
  • Terrapin Station
    7.8k
    Isn't it logically and metaphysically possible for the laws of physics to be different from what they are?Echarmion

    Part of my issue with the distinction is due to this. Does the distinction require that we're realists on physical law? I'm not sure.
  • frank
    2.3k
    :up:

    I've never really been convinced that the physical/metaphysical/logical distinction with respect to modality makes much sense.Terrapin Station

    Physical possibility is what's possible given the laws of physics.

    Since some metaphysical possible worlds contain a god who can do anything that's logically possible, the distinction between L and M possibility is minimal.
  • Terrapin Station
    7.8k
    Physical possibility is what's possible given the laws of physics.frank

    I'm familiar with the standard distinction. The issue is that I'm not sure that the standard distinction amounts to anything "substantial."

    For one, I'm not a realist on physical laws. So if there are no real physical laws, it's not going to make a lot of sense to analyze physical possibility on physical laws. It's also not going to make a lot of sense to suppose that physical laws could be different than they are.
  • frank
    2.3k
    If you're anti-realist about physical law, you're probably anti-realist about modality in general.

    IOW, it's hard to imagine you never speak in terms of counterfactuals. "If the surgeon hadn't had a seizure during her brain surgery..."

    You can just say we shouldn't analyze your speech. We should take it for its social function.
  • Echarmion
    303
    Yes. P is true at some logically and metaphysically possible worlds. It's also true at some L and M impossible worlds. The point being: we might imagine that possible world semantics is reducing modality to something non-modal, but it isn't. It's an unnecessary distraction. Modal distinctions are just as primitive in distinguishing possible from impossible worlds as they are in sorting out small scale events, so we can dispense with possible world semantics.frank

    I see. But even if we accept that modal statements can be rephrased via possible world semantics to be non-modal, we still need modal knowledge. That is, we need to know what worlds are possible to judge the statement.

    Good point. We probably won't be able to claim that knowledge of physical possibility is ever entirely empirical. But the problem of induction doesn't have a rational solution either, so it's a burden to both sides.frank

    My instinct here is to try to figure out what exactly my mind is doing when I go from a non-modal statement to a modal one. "Jack is at his house right now" is clearly a synthetic a posteriori statement. "It's possible that Jack is at his house right now" is also synthetic. What happened to the information in the statement? Part of it was lost, since the modal statement does not include Jacks current whereabouts. But we're still talking about Jack, and we still have some information about him (he's not dead, for example). So the statement must still be a posteriori. Have we just omitted some information? Made the statement more "fuzzy"?

    But If that's so, does that imply that a statement of possibly is categorically different from a statement of impossibility? It seems that "it's impossible for Jack to be at home right now" contains information that is different from the non-modal statement.

    Part of my issue with the distinction is due to this. Does the distinction require that we're realists on physical law? I'm not sure.Terrapin Station

    Interesting question. For something to be different it would have to have a fixed form in the first place, which might imply realism. Can we avoid that by referring to the structures that give rise to the apparent laws of physics?
  • Mww
    490


    My views:

    I’m familiar with some of the literature and I’m aware such literature makes explicit the theme “modal knowledge” by actually using the term. I think modality relating to knowledge is a misnomer. There is modality for concepts, logic, and foremost, experience. All those are antecedent to knowledge and are grounds for it, so it would seem that knowledge stands as given or not given as an end, modality belonging to its antecedents alone as its means.

    In other words, knowledge is already judged as possible, necessary or impossible. Pure a priori knowledge is already determinable by logic as to whether it will be possible, necessary or impossible. And a posteriori knowledge is already determined by the modality of the experiences relative to it.

    I understand propositions like, knowledge is possible, or knowledge is impossible, may be construed as the modality of knowledge, or modal knowledge. These are nonetheless seemingly contingents, always relative to their respective conditions, wherein the modality actually lies.

    Or not.........considering my admittedly pre-modern rationalism.
  • frank
    2.3k
    see. But even if we accept that modal statements can be rephrased via possible world semantics to be non-modal, we still need modal knowledge. That is, we need to know what worlds are possible to judge the statementEcharmion

    The idea is to dispense with possible world semantics. It serves no purpose.
    mind is doing when I go from a non-modal statement to a modal one. "Jack is at his house right now" is clearly a synthetic a posteriori statement. "It's possible that Jack is at his house right now" is also synthetic. What happened to the information in the statement? Part of it was lost, since the modal statement does not include Jacks current whereabouts. But we're still talking about Jack, and we still have some information about him (he's not dead, for example). So the statement must still be a posteriori. Have we just omitted some information? Made the statement more "fuzzy"?Echarmion

    There's an argument that possibility of P is entailed by actuality of P. Would you accept that without the argument?
  • frank
    2.3k
    I just meant knowledge of modality where we're talking about modes of truth.
  • Mww
    490


    Knowledge of modality; knowledge of modes of truth; knowledge of kinds of truth there are, how to find it, how to recognize it, what to do with it.

    OK. I’m back in line now. Thanks.
  • Echarmion
    303
    There's an argument that possibility of P is entailed by actuality of P. Would you accept that without the argument?frank

    The argument seems fairly obvious to me. But, if that is the case, then my second question becomes relevant: are there qualitative differences between modal statements? Possibility is included in actuality. But is impossibility or necessity included in some non-modal statement?

    Perhaps it is wrong to include statements of possibility in the same category as statements of necessity or impossibility. Or perhaps we are wrong when we think that actuality includes possibility, because possibility includes the possibility of counterfactuals.
  • frank
    2.3k
    But is impossibility or necessity included in some non-modal statement?Echarmion

    In possible world semantics necessarily true and false reduces to true or false in every possible world. The modalist denies this and holds that modality is simply speculation based on what we know. It should always be taken as: as far as we know. There is no justification for "extraordinary" claims (having to do with origins, for instance). There is no secure ground for those claims.

    This makes for an empirical-friendly approach to modality. But what's the flaw in it? How does a modal rationalist answer this?
  • frank
    2.3k
    Possible world semantics is appealing because of the way it fits a common and ancient analysis of language: all events take place in a completed world. To imagine a possibility not realized in the actual world is to imagine a different world. It became more cemented in 20th Century philosophy as a way to plug modal holes in predicate logic. Possible world semantics provides the means to preserve extensionality for modal sentences. Extensionality is important for certain artificial languages used by logicians.

    It has other uses such as providing for analysis of intension. But I'll stop here and say that the real basis of possible world semantics is a giant stipulation. It's accepted because it eases solutions to certain puzzles, but those puzzles are not aspects of ordinary language, and so the solutions are meaningless beyond a certain rigid scope.

    True?

    The goal here was to understand Chalmers' 2D argument against materialism. I think one of the key components of the argument requires that one be prone to lean toward rationalism in the first place.
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