[Zope3-dev] Re: Zope3-dev Digest, Vol 25, Issue 37

[Tim Peters]

[Benji York]
> ...
> We're drifting fatally off topic here, but: Just as there are some
> statements that cannot be expressed as dyadic predicates, are there also
> those which cannot be expressed as triadic predicates?
>
>     "John gives a book to Mary in exchange for 5 euros"
>
> If you store the relations "John gives a book to Mary" and "Mary gives 5
> euros to John" how will you know that the 5 euros were payment for the book?

Worse, this happened on a Sunday, in Brussels, while winds were
gusting from the south, and a nearby solicitor wearing a lime green
bowler hat advised them that their transaction was exempt from VAT ;-)

Even allowing relations of arbitrary arity, there are some kinds of
knowledge that can't be expressed in full-blown first-order logic. 
For example, Google will find lots of (mostly tedious <wink>)
discussion of the Geach-Kaplan sentence:

    Some critics admire only one another.