An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

IMMEDIATE INFERENCE. 91
The results of 9 to 12 are summed up
following table :
Original Proposition . SaP
PiS Converse . .
Obverse .
Contrapositive P
. SeP
. .
Inverse . . . S
A. E. L O.
SeP SiP SoP.
in the
PiS PiS none.
SaP SoP SiP .
eS P iS none P iS.
oP S iP none none.
13. A note may be added on the subjects of
"
Immediate Inference by added determinants,"
"
Immediate Inference by complex conception,"
and
"
Immediate Inference by converse relation."
The first-mentioned
same
process consists in adding the
"
"
determinant or qualification to the subject and
the predicate of the original proposition.
that "S is P," then it follows that "AS is AP "
If it be true
; or, in
Jevons s example, if "a comet is a material body," then
"
a visible comet is a visible material Provided
body."
that the qualification added to the predicate is in all
respects the same as that added to the subject, the truth
of the new proposition follows necessarily from the truth
of the original, just as the same quantity introduced
on both sides of an algebraic equation does not affect
the relation of equality. But in dealing with significant
terms it is necessary to guard carefully against the
ambiguity of language,
given by Jevons :
as is seen in the two instances
"All kings are men," therefore "All incompetent
kings are incompetent men."
"A cottage is a building," therefore "A huge cottage
is a huge building."
The fallacy is due, in such cases, to the fact that a
determinant which is intended to specify the subject (S)