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This question is ultimately a follow up to this one

For the context of the question, assume that a metaphysical reality is a reality that can be conceived without contradiction and that these realities are mutually exclusive. For example, “God operating in the world” and “the Christian God operating in the world” are not mutually exclusive. The former is implied by the latter. For example, one kind of reality may involve the Christian God who operates in the world. Or the Islamic God. Or some invisible spaghetti monster running the world. Etc

Let’s say that one argues that assignments of probabilities to different possible realities being true cannot reasonably be assigned. The rationale for this may be that probabilities seem meaningless or that even if they were meaningful, there is no justification to use the principle of indifference for them. The principle of indifference, as a reminder, states that probabilities among propositions with an absence of knowledge should be equiprobable.

If so, does this imply that one cannot think it to be less reasonable to believe that say the Undetectable Flying Spaghetti Monster is real than the Christian God? Presumably, if one did think this, one would be able to justify an epistemic probability that is higher for the Monster than the Christian God. But as mentioned before, one may refuse to do this.

As such, would one be inconsistent if one fails to assign probabilities but also deems it to think that a certain kind of reality is more reasonable to believe than another?

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    @Conifold I don’t see how that evades the meaninglessness of probability being applied here. How does one, for example, attach a figure to the probability of a Flying Spaghetti Monster existing? How does one show that that figure is smaller than that of the Christian God? And lastly, what does it mean for a certain kind of being to “more likely” exist than another, even if all of this is with respect to our reality? The conundrum seems to remain. Aug 30, 2023 at 22:44
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    In theory the ideal prior probability of a universe is a function of the minimum description length of the universe: the shortest program that exactly generates all the observations from that universe. In practice we don't know this probability exactly, but we can often get good approximations. The FSM and the Christian God are similar explanations, and so we'd expect them to have similar prior probabilities, and we can't say too much about which is higher. An explanation based on simple laws of physics would be a simpler explanation, and thus it would have a much higher prior probability.
    – causative
    Aug 30, 2023 at 22:50
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    So this rests on the assumption that a simpler theory has a higher prior probability. This again begs the question of why it should be as such even though it seems intuitive. One may even argue, as theologians do, that god is more simple. Lastly, what does it mean for a theory to have X probability of being true? Aug 30, 2023 at 22:56
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    Yeah I suppose the last part of your comment is what I was trying to find. If there is no objective basis for epistemic probabilities, I’m having a hard time justifying why a probability that presumably reduces to just a subjective degree of belief says anything about the world. Sure it may say something about us and what we would do or how we would act given certain scenarios. But how does this help us actually understand what is true about the world as a matter of fact? Aug 30, 2023 at 23:09
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    Probabilities are not properties of the events described, they are properties of your perspective about the events described. Your perspective is the result of repeatedly applying various heuristics and other mental rules to your observations. You should try to select mental rules that result in perspectives that result in taking effective actions in the world. It just so happens that probability is very useful for taking effective actions, considering that we don't know everything about the world; probability represents your own lack of knowledge about the world.
    – causative
    Aug 30, 2023 at 23:40

2 Answers 2

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One may not reasonably be able to assign probabilities to different metaphysical realities. But one could potentially assign probabilities to the output of a method of evaluating whether something is true, e.g. apply a method to some claims and see how many you get right.

If your method is "believe everything you see", you may misclassify dreams, illusions or other mental conjurations.

If you refine this to exclude dreams and verify what you see, your misclassifications would go down, and the method would have a higher accuracy percentage (even if you can't assign a probability to a particular dream being true).

There are also multiple probabilities to consider, which can be based on some combination of true positives, true negatives, false positives, and false negatives.

The problem of figuring out whether even one belief (beyond "I am") is true may not be trivial, considering the unprovability of the existence of external reality and other minds. This may e.g. lead to some form or variant of coherentism, and considering whether a particular model, when applied consistently, produces internally consistent results.

If you cannot independently verify whether a claim is true, in some way, then that claim cannot serve as support for a method. If a method produced no independently verified claims, then, under this view, it cannot be deemed "good", and it certainly cannot be deemed "better" than any method that has produced independently verified claims (even if unreliably, although if it also hasn't produced disproven claims, it's not necessarily "worse" either - we just wouldn't have enough information to trust it).

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  • "Excluding dreams" is ontically kosher; epistemically not: because the fact of the matter is we all enter dreams inadvertently but wake up knowingly. This asymmetry of recognizing the dream state makes knowing "This is not a dream" epistemically and hence ontically infeasible
    – Rushi
    Aug 31, 2023 at 8:19
  • @Rushi The important time to recognise that a dream is a dream is after you've woken up. Recognising this while dreaming is less important, because actions taken in a dream don't generally affect things outside of that dream (and most people also don't have much conscious control over actions taken in dreams in any case... or maybe that's just me; there is lucid dreaming, which involves taking conscious control, but this also involves knowing that you're dreaming). As for whether this is a dream, that relates back to what I said about coherentism.
    – NotThatGuy
    Aug 31, 2023 at 8:39
  • As someone who's experienced nested dreams [I once woke out from dream to waking 4 times] which landed me into this socalled waking state, to me it's a highly non academic question: Is there a fifth awakening waiting to happen?
    – Rushi
    Aug 31, 2023 at 9:06
  • Awww... You removed ur totem-top comment. I liked it though I'd be hard pressed to say why!
    – Rushi
    Aug 31, 2023 at 10:18
  • Boy, finding out the truth is hard work! Wouldn't you think we would know it by now? If billions of people haven't, maybe we should just move on to something more pressing?
    – Scott Rowe
    Aug 31, 2023 at 10:59
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As such, would one be inconsistent if one fails to assign probabilities but also deems it to think that a certain kind of reality is more reasonable to believe than another?

I think you have that backwards. Probability, also epistemic probability, is a mathematical model that will not perfectly fit reality (not even "epistemic reality"), but can be helpful in certain (many) situations. If in a certain situation you don't find assigning epistemic probabilities helpful (and you have a good case that what you're talking about is such a situation), then don't do it. Case closed. There is no rule that says probabilities should always be assigned, and if you can't it means XXX. It just means that here it doesn't seem convincing and helpful, nothing more than that. (Of course somebody else might do it, and then you are free to find their arguments convincing or not.)

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  • The "Here be dragons" part of the map. Mount Olympus, for example.
    – Scott Rowe
    Aug 31, 2023 at 10:55

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