From: Logical Language Group <lojbab>
Message-Id: <199411142123.AA02893@access2.digex.net>
Subject: Ralph believes someone is a spy
Date: Mon, 14 Nov 1994 16:23:00 -0500 (EST)
Cc: lojbab@access.digex.net (Logical Language Group)
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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.