W.V.O. Quine (in Word and Object, 1976) tells this story: Paul and Elmer agree on three things. Paul believes only one thing that Elmer does not believe.
The background of this problem is that believing produces no (countable and quantifiable) utterances. Now, apart from this, I tried to find out what happens technically if I assume sentences instead of utterances.
Elmer: believes that he and Paul agree on three things - and he believes that Paul believes something that he, Elmer doesn't believe. – Ok, that’s two (agreed) things that Elmer believes.
Paul: believes that he and Paul agree on three things - and he believes that Elmer doesn't believe something that he, Paul, believes. – That’s two (agreed) things that Paul believes.
There is a certain asymmetry in this that can be avoided.
Another way (I)
E: believes p /\ q /\ r
P: believes p /\q /\r /\s…
Let’s not take into account that anyone who believes p has to believe that he believes p and so on, because that leads to infinity and is not interesting here.
But in order to agree with Paul, Elmer must believe
E: E bel p /\ P bel p and so on. Or better
E: E bel (p /\ P bel p and so on)
That is then more than three things for Elmer – and more than four for Paul.
Another way (II)
E: E /\ P agree on p /\ E /\ P agree on q /\ E /\ P agree on r /\ E /\ P ~ agree on s
P: E /\ P agree on p /\ E /\ P agree on q /\ E /\ P agree on r /\ E /\ P ~ agree on s
Here we got four things both agree upon.
Another variant with index words:
E: “I and the other, we believe….”
P: “I and the other, we believe …”
The sentences are identical then, but we have a difference in the propositions.
One solution might be that the two don’t know of each other. Quine – in his Quinean way – gave a hint saying “Paul and Elmer are sons of colleagues”. Does anyone have another idea?
I modified this question according to my best information. Unfortunately I do not own the 1976 edition of Word and Object that is a longer text than the 1960 book. My German translation of 1980 is based on this 1976 English version.