Re: Re:virus: Nothing

Tim Rhodes (proftim@speakeasy.org)
Sun, 21 Feb 1999 01:32:01 -0800

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... )

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."