Re: What is a logical contradiction?

On Thu, 8 Jan 2009 23:23:29 +0100, Herbert Newman <nomail@invalid> said:
On Thu, 8 Jan 2009 20:13:05 +0000 (UTC) Chris Menzel wrote:

There are in fact semantic frameworks for first-order modal logic
with

You realize that the context of my claims is/was classical first-order
predicate logic? :-o

Since when? The topic of the thread is "What is a logical
contradiction?", full stop. Nowhere in the thread was there any overt
restriction to classical (nonmodal) first-order logic. Your claim about
the statements "A is not A" and "It is not the case that A is A" was
entirely general: "clearly both statements _mean_ the same". It is, in
fact, not so clear. It is of course true that there is only one way (up
to logical equivalence) of representing the meanings of these statements
in classical first-order logic, so in that rather restricted sense they
have the same meanings. But again, on the face of it anyway, that was
not your claim. Also, your interlocutor, though obviously confused,
seemed to be groping for the distinction between sentential and
predicate negation and it is, at the least, interesting to point out
that there are classical logical frameworks in which that distinction is
far from trivial.

.

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