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

IMMEDIATE INFERENCE. 89
process as applied to the O proposition, calling it
in this case, however, Conversion by Negation. Con
version by Negation is not a variety of Conversion
as accurately denned ;
it is simply another and an un
desirable name for Contraposition. And as is seen
in the above table, Contraposition is a process applic
able not only to the A and the O, but also to the E
proposition ; in the I proposition alone it yields no
result.
The process of obversion may of course be applied to the
converse and to the contrapositive of a : proposition the
student will find, for example, that the obverted contra-
positive of SaP is P aS , of SeP is P oS , and of SoP is
P oS .
The following are examples of contraposition.
(1) "All that glitters is not gold."
Primary implication, SoP,
"
Some glittering things
are not golden."
"
Obverse, SiP Some ,
glittering things are not-
golden."
which are not
Contrapositive, P iS, "Some things
golden are glittering things."
The proposition has a secondary implication, SiP,
" Some glittering things are golden."
"
Obverse, SoP Some ,
glittering things are not
other than golden."
Contrapositive, none.
(2) "Natives alone can stand the climates of Africa."
Primary implication, SeP,
"
None other than natives
are able to stand . . ."
Obverse, SaP , "All, other than natives, are
unable . . ."
Contrapositive, P "
iS,
are other than natives."
Secondary implication, SiP,
able .
. ."
Obverse, SoP ,
Contrapositive, none.
" No
Some, who are unable .
natives are unable
" Some
.
natives are
. . ."
.,