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

100 IMPORT OF PROPOSITIONS AND JUDGMENTS.
(1) "All S is all P" represents fig. 9.
(2)
(3)
(4)
"All S is some P" ..
"SomeS is all P"
"Some S is some P" ,.
(5) "No S is P" .,
any
fig. 10.
fig. u.
fig. 12.
fig. 13.
In the propositions (2), (3), and (4), as the student
will see ( 4), there are
some now means some only.
"
secondary implications," since
In the ordinary fourfold division the predicate is not
quantified, and we are forbidden to treat some as expressly
excluding all. This is the reason why the reconversion of
an A proposition leads to a sacrifice of part of what we
know :
(a] All S is P.
(b] Some P is S, converse of (a).
(c] Some S is P, converse of (b}.
In (b) the predicate S is in fact distributed, as we know
from (a\ but we cannot indicate this by any sign of quantity.
And when converting (b\ we cannot consider more than the
form of the proposition, and this does not warrant us in
taking S in its whole extent.
We have seen that the class view is a possible way of
regarding any proposition, but that it is not always the
natural interpretation ; for it is only in what are ex
pressly judgments of classification that we think of the
predicate as a class. In most propositions we think of
the predicate as adjectival, according to the predicative
view. Moreover, no mere class -interpretation of pro
positions could be entirely true, because extension and
intension cannot be completely separated. The only
way of distinguishing or identifying a class in thought
is by some of its qualities, which must therefore enter
into the signification of the terms standing as subject
and predicate. Hence these terms cannot be taken in