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

56
S is not P "
THE LOGICAL PROPOSITION.
by O. As Mr Keynes has suggested, the
propositions may be abbreviated thus : SaP, SeP, SiP,
SoP. The letters were chosen because A and I are the
first two vowels of affirmo^ I affirm, and E and O the
vowels of nego, I deny.
2. Propositions are also classified according to
modality, into (a) necessary, as "S must be P"; (b)
assertorial, "S is
P"; (c) problematic, "S may be P."
Jevons says,
"
The presence of any adverb of time, place,
manner, degree, &c., or any expression equivalent to an
"
adverb, confers modality on a proposition
not the ordinary use of the term. Most writers take dis
; but this is
tinctions of modality in propositions as referring only to
"
"
"
the difference between must be," and
is," may be."
The questions arising out of these distinctions are too
difficult to be pursued in an elementary work ; but we
must add a note on the expression of these propositions
in the typical forms A, E, I, O.
(a) The assertion of
necessity of course forms an A
" An equilateral triangle must be equi
proposition :
angular" means that every example of an equilateral
triangle will be found to be equiangular.
(b) The assertorial proposition, which makes a simple
"
the Ameri
unqualified statement as a matter of fact, as
can Indians are copper-coloured," will fall naturally into
one of the four classes. In the example given it is an
A proposition.
(c) The merely problematical proposition as "the
weather may be fine," "S may be P" gives us no
information about S; it
whether S is P or not."
"I only says, do not know
The nearest in meaning to
such a judgment, among the four typical forms, is the
particular proposition, affirmative or negative. The
logical meaning of "some" comes out best when we