At Sun, 21 Feb 1999 01:32:01 -0800, you wrote:
>
>Joe writes:
>
>>>>A=True
>>>>B=False
>>>>C=Meaningless
>>>>
>>>>If A, B or C and if ~A and ~B, then C.
>>>>Q.E.D.
>
>
>I wrote:
>>>Good job, fancypants! Now please prove your first conditional.
>
>
>>OK, then, give me a statement which is neither true nor false
>>nor meaningless, or admit that you can't; to falsify the syllogism,
>>the onus is on you to provide a disproving counterexample to
>>the conditional!
>
>
>Wow, your logic astounds me! But if all one needs to do is disprove:
>
>Only A or B or C.
>
>All you really need is a D. And any D will do here. (D=Meaningful springs
>to mind for some reason.. )
This is a meaningless statement as long as D remains undefined. Once D is defined, then it may be either true or false. Try again.
>Now go back to your logic books, Joe. I'm sure the next try will be closer
>to the mark. (You might re-read the chapters on conditional proofs, look
>for the one with the phrase "One final reminder regarding conditional proof
>is that _every_condional_proof_must_be_discharged."_ [1] )
>
>-Prof. Tim
>
>[1] Patrick J. Hurley. "A Concise Introduction to Logic." (1981, Wadsworth
>Publishing) Chaper 7.5: Natural Deduction in Propositional Logic/The
>Conditional Proof. Which goes on to say, "If this rule is ignored, any
>conclusion one chooses can be derived from any set of premises."
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Joe E. Dees
Poet, Pagan, Philosopher