The Short Case for Verificationism

I think a claim is meaningful if it’s possible to be true and possible to be false. Of course this puts a lot of work on “possible”.

That's not the standard verificationist claim, which is more that things are meaningful if they can be verified as true or false.

So, I think the crux of why I don't really agree with your general gist and why I'm guessing a lot of people don't, is we see meaningfulness as something bigger than just whether or not something is a fact (statement that has a coherent truth value). To most I think, something is meaningful if it somehow is grounded in external reality, not whether or not it can be assess to be true, and many things are meaningful to people that we can't assess the truthiness of. You seem to already agree that there are many things of which we cannot speak of facts, yet these non-facts are not meaningless to people. Just for example, you perhaps can't speak to whether or not it is true that a person loves their mother, but that love is likely quite meaningful to them. There's a kind of deflation of what you mean by "meaning" here that, to me, makes this position kind of boring and useless, since most of the interesting stuff we need to deal with is now outside the realm of facts and "meaning" by your model.

I think for your purposes you can just define meaningless as “neither true nor false” without detouring into possibility

I think I agree it makes verificationism a bit more plausible if you already find Tegmark IV plausible.

Regarding the quantum multiverse - yes, I agree, that is the usual way of thinking about things, moreover the usual thinking is that most ordinary statements about the future are similarly indeterminate. On the other hand, this isn’t the usual thinking about the cosmological multiverse. In a quantum multiverse, universes literally branch, in a cosmological multiverse, universes merely diverge. So, assuming the usual views about these multiverses are correct, would Level IV be like the quantum multiverse or would it be like the cosmological multiverse?

I can see both ways, but on reflection, it seems more natural to say it’s like the quantum multiverse. On the cosmological picture, for every consistent mathematical structure, you’ve got a separate self contained world, and there can be a lot of duplicate structure across worlds, but there can’t be duplicate worlds. It seems to make a weird distinction between worlds and the substructures in worlds. On the quantum picture, you can think of the observer as a mathematical structure in its own right, that is instantiated in many different larger structures, and there’s no fundamental notion of “world”.

So fine, this gives you something like verificationism.

You are making two claims..about whether ontological indeterminacy holds, and about the meaning of "meaning" .

Setting aside the second claim , the first claim rests on an assumption that the only way to judge a theory is direct empiricism. But realists tend to have other theoretical desiderata in mind..a lot would reject simulations and large universes on the basis of Occams Razor, for instance.

As for the rest..you might have a valid argument that it's inconsistent to believe in both empirical realism and large universes.

This is false. I actually have no idea what it would mean for an experience to be a delusion - I don't think that's even a meaningful statement.

I'm comfortable with the Cartesian argument that allows me to know that I am experiencing things.

Everything you're thinking is compatible with a situation in which you're actually in a simulation hosted in some entirely alien reality (2 + 2 = 3, experience is meaningless, causes follow after effects, (True ^ True) = False, etc, which is being manipulated in extremely contrived ways which produce your exact current thought processes.

There are an exhausting number of different riffs on this idea- maybe you're in an asylum and all of your thinking including "I actually have no idea what it would mean for an experience to be a delusion" is due to some major mental disorder. Oh, how obvious- my idea of experience was a crazy delusion all along. I can't believe I said that it was my daughter's arm [LW · GW]. "I think therefore I am"? Absurd!

If you have an argument against this problem, I am especially interested in hearing it- it seems like the fact you can't tell between this situation and reality (and you can't know whether this situation is impossible as a result, etc.) is part of the construction of the scenario. You'd need to show that the whole idea that "We can construct situations in which you're having exactly the same thoughts as you are right now, but with some arbitrary change (Which you don't even need to believe is theoretically possible or coherent) in the background" is invalid.

Do I think this is a practical concern? Of course not. The Cartesian argument isn't sufficient to convince me, though- I'm just assuming that I really exist and things are broadly as they seem. I don't think it's that plausible to expect that I would be able to derive these assumptions without using them- there is no epistemological rock bottom.

On the contrary, it's the naive realist model that doesn't pay rent by not making any predictions at all different from my simpler model.

Your model is (I allege) not actually simpler. It just seems simpler because you "removed something" from it. A mind could be much "simpler" than ours, but also less useful- which is the actual point of having a simpler model. The "simplest" model which accurately predicts everything we see is going to be a fundamental physical theory, but making accurate predictions about complicated macroscopic behavior entirely from first principles is not tractable with eight billion human brains worth of hardware.

The real question of importance is, does operating on a framework which takes specific regular notice of the idea that naïve realism is technically a floating belief increase your productivity in the real world? I can't see why that would be the case- it requires occasionally spending my scare brainpower on reformatting my basic experience of the world in more complicated terms, I have to think about whether or not I should argue with someone whenever they bring up the idea of naïve realism, etc. You claim adopting the "simpler" model doesn't change your predictions, so I don't see what justifies these costs. Are there some major hidden costs of naïve realism that I'm not aware of? Am I actually wasting more unconscious brainpower working with the idea of "reality" and things "really existing"?

If I have to choose between two models which make the exact same predictions (i.e. my current model and your model), I'm going to choose between the model which is better at achieving my goals. In practice, this is the more computationally efficient model, which (I allege) is my current model.

This is only true for trivial values, e.g. "I terminally value having this specific world model".

For most utility schemes (Including, critically, that of humans), the supermajority of the purpose of models and beliefs is instrumental. For example, making better predictions, using less computing power, etc.

In fact, humans who do not recognize this fact and stick to beliefs or models because they like them are profoundly irrational. If the sky is blue, I wish to believe the sky is blue, and so on. So, assuming that only prediction is valuable is not question begging- I suspect you already agreed with this and just didn't realize it.

In the sense that beliefs (and the models they're part of) are instrumental goals, any specific belief is "unnecessary". Note the quotations around "unnecessary" in this comment and the comment you're replying to. By "unnecessary" I mean the choice of which beliefs and which model to use is subject to the whims of which is more instrumentally valuable- in practice, a complex tradeoff between predictive accuracy and computational demands.