Logic -- Juvenile literature; Logic, Symbolic and mathematical
2. Syllogisms
Now suppose we divide our Universe of Things in three ways, with regard
to three different Attributes. Out of these three Attributes, we
may make up three different couples (for instance, if they were a,
b, c, we might make up the three couples ab, ac, bc). Also suppose
we have two Propositions given us, containing two of these three
couples, and that from them we can prove a third Proposition containing
the third couple. (For example, if we divide our Universe for m,
x, and y; and if we have the two Propositions given us, "no m are
x'" and "all m' are y", containing the two couples mx and my, it
might be possible to prove from them a third Proposition, containing
x and y.)
In such a case we call the given Propositions 'THE PREMISSES', the
third one 'THE CONCLUSION' and the whole set 'A SYLLOGISM'.
Evidently, ONE of the Attributes must occur in both Premisses; or
else one must occur in ONE Premiss, and its CONTRADICTORY in the
other.
In the first case (when, for example, the Premisses are "some m
are x" and "no m are y'") the Term, which occurs twice, is called
'THE MIDDLE TERM', because it serves as a sort of link between the
other two Terms.
In the second case (when, for example, the Premisses are "no
m are x'" and "all m' are y") the two Terms, which contain these
contradictory Attributes, may be called 'THE MIDDLE TERMS'.
Thus, in the first case, the class of "m-Things" is the Middle
Term; and, in the second case, the two classes of "m-Things" and
"m'-Things" are the Middle Terms.
The Attribute, which occurs in the Middle Term or Terms, disappears
in the Conclusion, and is said to be "eliminated", which literally
means "turned out of doors".
Now let us try to draw a Conclusion from the two Premisses--
"Some new Cakes are unwholesome;
No nice Cakes are unwholesome."
In order to express them with counters, we need to divide Cakes in
THREE different ways, with regard to newness, to niceness, and to
wholesomeness. For this we must use the larger Diagram, making x
mean "new", y "nice", and m "wholesome". (Everything INSIDE the
central Square is supposed to have the attribute m, and everything
OUTSIDE it the attribute m', i.e. "not-m".)
You had better adopt the rule to make m mean the Attribute which
occurs in the MIDDLE Term or Terms. (I have chosen m as the symbol,
because 'middle' begins with 'm'.)
Now, in representing the two Premisses, I prefer to begin with the
NEGATIVE one (the one beginning with "no"), because GREY counters
can always be placed with CERTAINTY, and will then help to fix the
position of the red counters, which are sometimes a little uncertain
where they will be most welcome.
Public-domain text, read in full here on John Shaqi.
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