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Re: [bpfk] CLL Check: Only If
On Sat, Oct 30, 2010 at 2:00 AM, Robin Lee Powell
<rlpowell@digitalkingdom.org> wrote:
>
> Apologies for the HTML. Here's what's in the books as far as I can
> tell:
>
> - -------------
>
> <p><a href="../4/#e10">Example 4.10</a>, which uses the TFTT truth function, is subject to the same rules: the stated gloss of TFTT
> as “only if” works naturally only when the right-hand bridi is true; if it is false, the left-hand bridi may be either true or false
> . The last gloss of <a href="../4/#e10">Example 4.10</a> illustrates the use of “if ... then” as a more natural substitute for “only
> if”.</p>
> <pre>
> <a id="e10" name="e10">4.10)</a> la djan. nanmu .inaja la djeimyz. ninmu
> John is-not-a-man or James is-a-woman.
> John is a man only if James is a woman.
> If John is a man, then James is a woman.
> </pre>
>
> - -------------
>
> "if it is false, the left-hand bridi may be either true or false"
> is, as far as I can tell, wrong. The t,f case is false here.
>
> Am I missing something? What should this say?
The intention probably was:
<<
the stated gloss of TFTT as “only if” works naturally only when the
right-hand bridi is *false*; if it is *true*, the left-hand bridi may
be either true or false.
>>
But I find the whole discussion between examples 4.8 and 4.10 somewhat
confusing. The examples should not use tendentiously true ("John is a
man") or false ("James is a woman") statements. They should use
neutral statements, that can be either true or false, as well as being
causally unrelated. Say "John's car is blue" and "James' car is red".
John's car is blue only if James' car is red.
tells us something about the color of John's car when we know that
James' car is not red. When we know that James' car is red, that
sentence doesn't tell us anything about the color of John's car. That
may be what is being called "unnatural", something like
"uninformative". In the English gloss we expect this sentence to be
information about John's car, because "John's car" is the subject. If
we know that James' car is red, that sentence, if true, is
uninformative (and hence somewhat "unnatural", we don't usually go
around stating empty truths).
The difference with the Lojban is that "if" and "only if" are
subordinators in English, while ".inaja" and ".ijanai" are proper
sentence connectives. So in Lojban there is no reason to expect this
statement to be information about John's car any more than it could be
information about James' car. That's where the "unnaturality" comes
from, I suppose.
mu'o mi'e xorxes
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