hyporational comments on Mainstream Epistemology for LessWrong, Part 1: Feldman on Evidentialism - Less Wrong

16 Post author: ChrisHallquist 16 November 2013 04:16PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Article Navigation

Comments (82)

Comments (82)

You are viewing a single comment's thread. Show more comments above.

Comment author: hyporational 18 November 2013 10:55:43AM *  0 points [-]

I think the problem with what you're doing is that you're trying to analyze truth in terms of probability assignment. That's backwards.

Not really. If you can't establish what truth is, then probability obviously can't be an expression of your beliefs in relation to truth.

The whole business of assigning probabilities to statements presupposes a notion of truth, of statements being true or false.

The business of assigning probabilities presupposes that you can have some trust in induction, not that there has to be some platonic truth out there. Such a notion of truth is useless, because you can never establish what that truth is.

When I say that I assign a probability of 0.6 to a particular proposition, I'm expressing my uncertainty about the truth of the proposition, or the odds at which I'd take a bet that the statement is true (or, more operationally, that any evidence obtained in the future will be statistically consistent with the truth of the statement).

I'd say probability is more of an expression of your previous experiences, and how they can be used to predict what comes next. Why do induction and empiricism work? Because they have worked before, not because you're presupposing a true world out there.

So to even talk coherently about the significance of probability assignments, you need to talk about truth. If you now try to define truth itself in terms of probability assignments, you end up with vicious circularity.

That's why we need axioms. It seems to me axioms are not the kind of truth that JTB presupposes. I'm not saying we don't need mathematical truths or axioms that are agreed upon. I'm saying that presupposing the true territory out there doesn't add anything to the process of probabilistic reasoning.

If you mean establish it with absolute certainty, then I don't think that's possible.

That's what I mean, and that's what you would need if you think having that kind of a notion of truth is needed for probabilistic reasoning.

There's no difference between establishing the proposition P (e.g. establishing that Barack Obama is President), and establishing that the proposition P is actually true (e.g. establishing that "Barack Obama is President" is a true statement). If you know how to do the former, then you know how to do the latter. Adding "is actually true" at the end doesn't produce any new epistemic requirements.

I agree.

Comment author: pragmatist 18 November 2013 01:08:00PM *  0 points [-]

The business of assigning probabilities presupposes that you can have some trust in induction, not that there has to be some platonic truth out there. Such a notion of truth is useless, because you can never establish what that truth is.

I don't know what you mean by "platonic truth". I suspect you are thinking of something much more metaphysically freighted than necessary. The kind of truth I'm talking about (and I think most people are talking about when they say "truth") very much can be established. For instance, I can establish what the truth is about the capital of Latvia by looking up Latvia on Wikipedia. I just did, and established the truth of the proposition "The capital of Latvia is Riga." Sure this doesn't establish the truth with 100% certainty, but why should that be the standard for truth being a useful notion?

Truth is not something you need God-like noumenal superpowers to determine. It's something that can be determined with the very human superpowers of empirical investigation and theory-building.

I'd say probability is more of an expression of your previous experiences, and how they can be used to predict what comes next.

I assign probabilities to past events, to empirically indistinguishable scientific hypotheses, to events that are in principle unobservable for me. Am I just doing it wrong, in your opinion?

That's what I mean, and that's what you would need if you think having that kind of a notion of truth is needed for probabilistic reasoning.

What kind of a notion of truth? The kind that requires absolute certainty? But I'm not aware of anyone arguing that one needs that kind of truth for the JTB account, or to make sense of probabilistic reasoning. Why do you think that kind of notion of truth is needed?

Comment author: hyporational 18 November 2013 01:14:08PM *  0 points [-]

I'm not arguing for any kind of notion of truth. I thought the kind of notion of truth JTB seems to be assuming is confusing as hell, and I wanted clarification for what it was trying to say.

My objection started from here:

2) You're misunderstanding the purpose of "true" in the JTB definition. It's not a matter of assigning probability 1 to a proposition, it's a matter of the proposition actually being true.

Can you get back to that, because I don't understand you anymore?

Comment author: pragmatist 18 November 2013 01:19:44PM *  1 point [-]

OK, I guess we were talking past each other. What is it about that particular claim that you find objectionable? I thought what you were objecting to was the notion that a proposition being true is distinct from it being assigned probability 1, and I was responding to that. But are you objecting to something else?

Is your objection just that you don't understand what people mean by "true" in the JTB account? I don't think they're committed to any particular notion, except for the claim that justification and truth are distinct. A belief can be highly justified and yet false, or not at all justified and yet true. Pretty much any of the theories discussed here would work. My personal preference is deflationism.

Comment author: hyporational 18 November 2013 01:36:02PM *  0 points [-]

ETA: I posted this also on the top of this comment thread, so you can answer there if you wish.

The way I read the quote is:

A proposition being true doesn't mean that it has the probability of 1. It does however mean that if a proposition is assigned a probability of 0.9, and it coincides with what the world is actually like, it is true.

This in turn could be read as:

A proposition being true doesn't mean that is has the probability of 1. It does however mean that if a proposition is assigned a probability of 0.9, and it coincides with what we know about the world with probability of 1, it is true.

Do you now understand my objection? I predict it's based on some grave misunderstanding. Thanks for the link, I'll try to check it out when I have more time.

Powered by Reddit Powered by Reddit