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

IMMEDIATE INFERENCE. 77
The essentials of the doctrine of opposition which we
have explained were clearly stated by Aristotle. He
says that formally (Kara Tr\v Xet*>, An. Prior., ii. 15)
there are four kinds of opposition :
(a)
when one asserts of the whole what the other
denies of the part (A and O) ;
(d)
when one denies of the whole what the other
asserts of the part (E and I).
In both these cases the propositions are said to be
opposed as contradictories (avrifyaTiicws avruKelcrOai).
Contradictory propositions admit of no third alternative,
and there is no middle way between them. The two
other forms of opposition mentioned by Aristotle are :
(c) when one proposition
the other denies of the whole (A and E) :
affirms of the whole what
in this case
they are said to be contraries (eWzmo)? avriicelaOai),
and both may be false.
(d) When one affirms of a part what the other denies
of a part (I and O). In this case Aristotle says quite
truly that the
"
"
is opposition merely verbal.
Part III. Immediate Inference.
8. Immediate Inference is the name given to the
process by which, from a single given proposition, we
derive another whose truth is implied in the former. 1
Hence opposition is a variety of Immediate Infer
ence ;
E and O, and the truth of I : from
for from the truth of A we may infer the falsity of
falsity of A and I, and the truth of O :
the truth of E, the
from
the truth
1 The process is rather a transformation of the proposition than
an addition to our knowledge ; hut it is more than a merely verbal
change (see ch. V. i).