Charles,
What you said is correct for most formal logics formulating binary
deduction, using model-theoretic semantics. However, Edward was
talking about the categorical logic of NARS, though he put the
statements in English, and omitted the truth values, which may caused
some misunderstanding.
Pei
On 10/7/07, Charles D Hixson <[EMAIL PROTECTED]> wrote:
> Edward W. Porter wrote:
> >
> > So is the following understanding correct?
> >
> > If you have two statements
> >
> > Fred is a human
> > Fred is an animal
> >
> > And assuming you know nothing more about any of the three
> > terms in both these statements, then each of the following
> > would be an appropriate induction
> >
> > A human is an animal
> > An animal is a human
> > A human and an animal are similar
> >
> > It would only then be from further information that you
> > would find the first of these two inductions has a larger
> > truth value than the second and that the third probably
> > has a larger truth value than the second..
> >
> > Edward W. Porter
> > Porter & Associates
> > 24 String Bridge S12
> > Exeter, NH 03833
> > (617) 494-1722
> > Fax (617) 494-1822
> > [EMAIL PROTECTED]
> >
> Actually, you know less than you have implied.
> You know that there exists an entity referred to as Fred, and that this
> entity is a member of both the set human and the set animal. You aren't
> justified in concluding that any other member of the set human is also a
> member of the set animal. And conversely. And the only argument for
> similarity is that the intersection isn't empty.
>
> E.g.:
> Fred is a possessor of purple hair. (He dyed his hair)
> Fred is a possessor of jellyfish DNA. (He was a subject in a molecular
> biology experiment. His skin would glow green under proper stimulation.)
>
> Now admittedly these sentences would usually be said in a different form
> (i.e., "Fred has green hair"), but they are reasonable translations of
> an equivalent sentence ("Fred is a member of the set of people with
> green hair").
>
> You REALLY can't do good reasoning using formal logic in natural
> language...at least in English. That's why the invention of symbolic
> logic was so important.
>
> If you want to use the old form of syllogism, then at least one of the
> sentences needs to have either an existential or universal quantifier.
> Otherwise it isn't a syllogism, but just a pair of statements. And all
> that you can conclude from them is that they have been asserted. (If
> they're directly contradictory, then you may question the reliability of
> the asserter...but that's tricky, as often things that appear to be
> contradictions actually aren't.)
>
> Of course, what this really means is that logic is unsuited for
> conversation... but it also implies that you shouldn't program your
> rule-sets in natural language. You'll almost certainly either get them
> wrong or be ambiguous. (Ambiguity is more common, but it's not
> exclusive of wrong.)
>
>
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