Re: Testing Validity in FOPL-A


George Dance wrote:
> George Dance wrote:
> [correction added]
>
> > Of all the inferences of traditional syllogistic logic, only
> [contraposition]
> > (of the A and O propositions) and obversion (in one direction) come out
> > invalid in FOPL-A.
>
> snip
>
> > V. Contraposition
> > V.i. All S is P and All non-P is non-S are not equivalent. (B)
> > V.ii. No S is P and No non-P is non-S are not equivalent.
> > V.iii. Some S is P and Some non-P is non-S are not equivalent.
> > V.iv. Not all S is P and to Not all non-P is non-S are not equivalent.
> > (B)
>
> snip

It's perhaps necessary to add that conversion by contra of the A and O,
and obversion in both directions, are valid if one presupposes that no
terms are empty.

.

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