Does "If A then B mean if not B then not A" ?
DJNordlund at aol.com
DJNordlund at aol.com
Thu Jun 28 21:17:49 EDT 2001
In a message dated 6/28/2001 1:14:33 PM Pacific Daylight Time,
rickstamp at gmx.net writes:
>I have seen it stated that it is a logical fallacy when one assumes that a >
conditional statement is also true in the reverse as in "If A, then B is not
equal to
>if non-A, then non-B) as described by Wallace on page 687. Could one also >
state that this is also the case for "if not B then not A"? Assume a third
class >conditional with EAN + subjunctive followed by an apodosis in the
future.
>Sincerely,
>Rick Stamp
Rick,
when you have a valid implication such as
(1) if A then B
you are correct in understanding that it is NOT logically valid to claim
(2) if not-A then not-B
However, if (1) above is valid, then it IS valid to conclude
(3) if not-B then not-A
regardless of the Greek you are analyzing.
Hope this is helpful,
Dan Nordlund
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