[lojban] Re: what's a du'u?

[Jorge Llambías <jjllambias@gmail.com>]

On Sat, Dec 5, 2009 at 6:06 AM, Thomas Jack <thomasjack@gmail.com> wrote:
> 2009/12/4 Jorge Llambías <jjllambias@gmail.com>:
>>
>> I don't think it's true in general. It's true only if the sumti "la
>> tom" and "la tomas" have been assigned the same value outside of the
>> du'u context.
>
> Yes, does my "given that all the names refer to the same person" not
> take care of this?

Only if you assume that names are simply variables that get assigned a
value and then that's it, every new use of the name is just a
reference to that value. But in practice names don't work like that,
as a rule every new use of a name may have to be interpreted afresh.
Of course context plays an important role and you do expect a repeated
name to get assigned the same value again. But du'u very often sets a
context where this assumption is likely to break down.

>The problem is that, even if all the names refer to
> the same person, common English usage (and perhaps common Lojban
> usage?) suggests that {lo du'u la tom du la tom} and {lo du'u la tom
> du la tomas} are different (compare to "that tom is tom" and "that tom
> is thomas" in English).

Right. That's because the value assignment proceeds independently for
each use, even if the final value ends up being the same.


> My problem is that I don't think there is a problem with such a
> theory—one such theory is my current favorite. Someone who knows that
> Tom is Tom, but says they don't believe the proposition that Tom is
> Thomas, is simply mistaken.

Those are two different uses of names: either their values are fixed
once and forever, or they are calculated dynamically in context. I
believe the latter is more in accordance with what goes on in
practice.

> I started this thread because one theorist
> arguing for such a theory suggested that maybe we should speak a
> language which respects this theory, and I immediately wondered
> whether Lojban does. Investigating the meanings of {du'u} and {bridi}
> suggested that, in fact, it does, but I am not sure.

I suspect this is not something we can define by fiat, that it is in
the nature of language that meaning is something dynamic. This issue
isn't really restricted to names either, the same argument can be made
about two references to the same thing using different descriptions.

> If a du'u is a predication, what is a predication? An assertion of a
> relationship between some arguments?

Well, it is not an assertion. An assertion is just one of the many
possible uses of a proposition. The most obvious example where a du'u
is not an assertion is in "no da xusra lo du'u ..."

>What, then, are the arguments? If
> they are the things referred to in the sentence, it seems to me that
> {lo du'u la tom du la tomas} must be the very same predication as {lo
> du'u la tom du la tom}, since the things referred to in both are the
> same.

Then a du'u must involve something more than a relationship between
arguments, it must also involve the way the arguments are identified.
Or, alternatively, we might say that the way that the arguments are
identified is part of the relationship, so that the relationship
between the arguments is not fully expressed by the selbri alone.

> Suppose you believe that Tom is rich. Then, you meet a beggar on the
> street named Thomas, and (because he's begging) come to believe that
> Thomas is poor. You don't realize that Tom and Thomas are the same
> person. You then say {mi na krici lo du'u la tomas ricfu}. Are you
> right or wrong?

It will depend on what "lo du'u la tomas ricfu" refers to.

> I want to ignore the weirdness that Lojban's
> context-sensitivity can give rise to (I think {ko'a broda ko'e} and
> {ko'a na broda ko'e} are not contradictory in suitable contexts). I
> think that if a du'u is a predication, the arguments of which are
> things referred to, you are wrong. You DO believe that Thomas is rich.
> Your problem is that you don't realize that the proposition that
> Thomas is rich and the proposition that Tom is rich are, in fact, the
> very same proposition (predication?).

I don't see a problem with that. The string  "lo du'u la tomas ricfu"
can be used to refer to different propositions, one of which is closer
to "the person that I met on the street is rich" and the other is
closer to "the person that I know as 'Tom' is rich". In the context
you described, it is more likely to refer to something closer to the
first, because the speaker has no reason to use it to refer to
something closer to the second. But someone else might use those same
words to refer to something closer to the second.

The problem arises if you insist that "lo du'u la tomas ricfu" can
refer to one and only one proposition, no matter what the
interpretation.

> If you are not wrong, I think
> that a du'u must wrap up more than just the things referred to. And
> it's not just the particular reference assignments inside the du'u
> that matter—all names in all of my examples refer to the very same
> person. Rather it's the manner in which they're referred to that
> matters.

Yes, I would say it is the assignment process that matters.

>  If your utterance of {mi na krici lo du'u la tomas ricfu} is
> true, the fact that {la tomas} was used to refer to Tom, rather than,
> say {la tom}, must be wrapped up somehow in the du'u (and so the du'u
> must be more than just a predication as I understand "predication").

Yes, I would say that the choice of words can have an effect on the meaning.

There are different approaches to explain why that is the case. One
approach is to say that there are fixed entities out there (one of
which is Tom) and that the different ways to refer to those fixed
entities end up producing a different du'u. Another approach is to say
that there is no such thing as a fixed entity out there, and then the
du'u are different simply because each one is describing a different
'world', with different entities.

But whichever way you go, it doesn't seem reasonable to claim that
it's logically impossible for someone to not know whether Tom is
Thomas. That's just not the way names are used in language.

mu'o mi'e xorxes


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