Ralph believes someone is a spy

[Logical Language Group <lojbab@ACCESS.DIGEX.NET>]

I sent this message by private mail back in April to a participant in
another mailing list.  I have deleted all identifying information about
the recipient.  (Since I hold copyright in the message, I am free to do this.)

The poster wrote:

> > A thought came to me from my philosophy class.  To not believe in
> > something, one must acknowledge its existence.  ex.  To consciously not
> > be prejudiced requires knowledge of prejudice.  To not believe in God
> > requires acknowledgment of God's existence (this is theory, not
> > necessarily my belief - I haven't come to terms with this one yet).

I replied:

> There are two meanings, in English, of the word "believe", usually called
> the "relational sense" and the "notional sense". To understand the difference,
> consider this example, due to Quine:
>
> "Ralph believes somebody is a spy" is ambiguous.  It can be understood as
>
> 1)    (Ex) (Ralph believes (x is a spy))
>
> which in English is "There is somebody whom Ralph believes to be a spy",
> or as
>
> 2)    Ralph believes ((Ex) (x is a spy))
>
> which in English is "Ralph believes that there exists somebody who is a
> spy", roughly "Ralph believes there are spies."
>
> Most Ralphs will agree with (2) but not with (1), since most people do
> not believe that some specific person is a spy, although most people do
> believe that spies exist.
>
> The case of disbelief is even more complicated, since the negation
> "Ralph does not believe there is a God" has many different logical
> interpretations:
>
> 3)    (Ex) (x is God) . (Ralph believes (~ (x exists)))
>       God exists, and Ralph believes he does not exist.
>
> 4)    (Ex) (x is God) . ~ (Ralph believes (x exists))
>       God exists, and it isn't true that Ralph believes he exists.
>
> 5)    Ralph believes (~ (Ex) (x is God))
>       Ralph believes that nothing exists which is God.
>       = Ralph believes there is no God.
>
> 6)    ~ (Ralph believes ((Ex) (x is God))
>       It is not true that Ralph believes that God exists.
>
> Statements 5 and 6 do not presuppose the existence of God.  (BTW, 6 represents
> my personal view: I am an agnostic.)
>
> Feel free to print this out and show it to your philosophy professor.
> The symbol "(Ex)", meaning "there exists an x" should really have a backwards
> E, but ASCII doesn't have that character.

I later found out that the philosophy class in question was not ongoing,
as I had supposed, but some 5 years ago.  However, the distinctions made
here are quite relevant to the question of opacity.

--
John Cowan              sharing account <lojbab@access.digex.net> for now
                e'osai ko sarji la lojban.