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

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CHAPTER IV.
THE IMPORT OF PROPOSITIONS AND JUDGMENTS.
i. THE question of the import of propositions is
this : what kind of relation between subject and predi
cate do logical propositions express, when stated in
one of the four forms A, E, I, O ?
Throughout the last chapter we have been dealing
with Subject and Predicate as representing classes,
which is the simplest way to regard them when studying
Opposition, Immediate Inference, and the syllogistic
forms to be described in the following chapter. There
are, however, four possibilities, 1 since both Subject and
Predicate may be read in Intension or Extension.
"
Take the proposition Man is mortal." This may be
interpreted in four ways
(1) Subject in extension, predicate in intension,
"All the class men have the attributes of
"
mortality.
(2) Subject and predicate in extension,
" The class man is included in the class mortal
beings."
(3) Subject and predicate in intension,
" The attributes signified by humanity are
always accompanied by those of mortality}
1 These four numerically possible cases are arrived at in a purely
arithmetical and external way. The fourth case was added by
Dr Keynes.
G