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

52
THE LOGICAL PROPOSITION.
we make an assertion we must either (i) affirm some
thing of the subject we speak of, or (2) deny something
of it. Again, the affirmation or denial may be made
(a) of some one particular thing, or (b) of a whole class
or kind of things, or (c) of a part of such a class, or (d)
the proposition may be expressed without saying whether
the whole or a part is meant. Later logicians called the
former division (affirmative and negative) one of quality,
and the latter (which is concerned with the distinction
of the part and the whole of a class) one of quantity.
According to quality, then, propositions
are either
affirmative or negative. Aristotle is fond of saying
that the affirmative unites or combines, the negative
divides or separates. What kind of union, or separa
tion, does the proposition express? The affirmative
expresses a union between Subject and Predicate in the
sense that the attributes signified by the predicate be
long to the subject : thus in the proposition
"
Fixed
stars are self-luminous," the quality of shining by their
own light is said to belong to the heavenly bodies called
fixed stars. The negative expresses a separation of
subject and predicate
in the sense that the attributes
signified by the predicate do not belong to the subject ;
"
gold is not easily fusible," declares that the quality of
being easily fusible does not belong to gold. The
typical forms, in Logic, of affirmation and negation
are S is P, S is not P. The student should bear in
mind that in this formal expression of the negative pro
position, the word
"
"
not belongs to the copula l :
Subject Copula Predicate
S is not P
1 The philosophical aspects of Negation will be further considered
in ch. XI. 5.