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Fwd: Re: [jboske] Opacity and belief

The moment someone mentions philosophy, I ask pc. I know less about philosophy than I do about logic.


From: Pycyn@aol.com
Date: Fri, 17 Jan 2003 19:12:23 EST
Subject: Re: [jboske] Opacity and belief
To: lojbab@lojban.org

In a message dated 1/17/2003 1:58:48 PM Central Standard Time, lojbab@lojban.org writes:
The sentence
>"lu la kikeron. krecau li'u du lu la tulius. krecau" is false, because
>the contexts of "la kikeron." and "la tulius." are both *opaque*: equals
>cannot be replaced with equals *salva veritate*.

No, it is false because they are different sentences and {du} claims that they are the same. They ARE materially equivalent (i.e., both true in the actual world) but that is not about identity of sentences, only about identity of facts. {la kikeron} and {la tulius} are not opaque, they are merely material mode, i.e., not naming MTC but rather the two words (mentioning, not using -- something different from opacity).

What we haven't nailed down is the abstract bridi "du'u la
>kikeron. krecau" and "du'u la tulius. krecau"? Are these true of
>different (noematic) objects, or of the same object? The difference is
>important because Ralph, who does not know that Cicero is Tully, believes
>(i.e. is disposed to assent to the claim) that Cicero is bald but does
>not believe (i.e. withholds assent from the claim) that Tully is bald.

For as long as Loglan or Lojban has been around, things like {du'u} have marked off intensional contexts, opaque to external reference and quantification. This has been "nailed down" since 1955; why is it coming up again?

If du'u-contexts are truly opaque, then we don't know what it means to
>insert variables in them that are quantified outside the du'u.

Not so. "Quantifying in" is not a problem, it is quantifying out. That is, what do variables bound within the context mean externally (and remember that proper names are quantifiers in Montagovia).

But then what is the status of "da poi du me la kikeron. zo'u la ralf.
>krici lo du'u da krecau"? Is this true iff Ralph is disposed to assent to
>"Cicero is bald"? What if he is disposed to assent to "Tully is bald"?
>What if he is not disposed to assent to either, but is disposed to assent
>to "The greatest Roman orator is bald" (supposing that he has no name
>for this man). We don't know because the critical mode of presentation
>material is outside the du'u-bridi.

It is true just in case he assents to the claim that Cicero is bald under some mode of presentation that in fact gives Cicero in this world, since it is in this world that the object is identified. The problem case is with {la ralf krici la kikeron cu krecau}, since {la kikeron} may be -- in Ralph's ideational world -- anybody at all, including bodies that aren't in this world. {krici} has an out other than prenexing, namely the third place, for subject, but that is incidental -- and may be opaque as well, though I don't think it should be.

>We can't waffle on this stuff. We have to be able to establish the truth
>value of "lo du'u ... cu du lo du'u ..." where the ellipsized sentences
>are the same except for interchanging singular terms of identical
This is always false except in the rare cases where the singular terms are NECESSARILY coreferential (no cases come to mind -- Anselm thought "God" and "that than which nothing greater can be conceived" worked, but it doesn't seem to).

If we make them opaque, we have problems with exterior
>restrictions on quantification: how, if at all, are they imported?

As noted earlier, it is exporting that is a problem: given that there is something I believe to be blue, then I believe something is blue, but NOT conversely (I believe Snow White to be blue, but there ain't no Snow White, so -- on this evidence at least -- there is not something I believe to be blue).

If we make them equal (transparency), then we can't move
>between beliefs and dispositions-to-assent, which seems counterintuitive
>and dire.
While disposition to assent is not a great trick for belief, that is for reasons other than that this fails logically. And this identification of propositions sucks for reasons that it screws up the (faulty) instrumentalist test for beliefs.

I mention -- just to make life thoroughly miserable -- that we can dodge this issue if all nonexistents are also available in the range of our variables. Of course, this does not help much, since we can repeat the question with restricted quantification (and of course, we get messy things like: for every property there is something (possibly nonexistent) that has it).

Repeating, there is NO problem about quantifying over terms inside {du'u} expressions or about identifying them with other terms. You just can't do it salve veritate. The problem only arises if you try to, so don't.

-- lojbab lojbab@lojban.org Bob LeChevalier, President, The Logical Language Group, Inc. 2904 Beau Lane, Fairfax VA 22031-1303 USA 703-385-0273 Artificial language Loglan/Lojban: http://www.lojban.org