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

AND THE LAWS OF THOUGHT. 41
premises ; but the principle may
be made universal. If
any system of doctrines or set of statements is true,
they must be consistent among themselves.
The dictum that only
"little minds" burden themselves
with the effort of attaining to a rigid consistency, expresses a
truth which has a practical and not a logical bearing. We
must not sacrifice ideas which contain truth because we
cannot make them self- consistent in the precise form in
which we have them before us. It is possible to be assured
-through a power of "judging" (not logically judging)
which is developed by life and experience that certain ideas
are fundamentally true, while yet we cannot exhibit their
consistency in a satisfactory logical form. To sacrifice truth
in such cases for the sake of a rigid logical consistency, is
simple or rather complex folly. Yet this does not alter the
fact that, so far as the ideas are true, to that extent they are
self-consistent. 1
12. The Law of Contradiction, that the proposi
"
"
cannot both be true
tions "A is B
and "A is not B
together, is another aspect of the Law of Identity, and
corresponds to it in meaning.
(a) Just as the principle of Identity
secures the
identical reference of a term to a meaning, so the prin
ciple of Contradiction secures the same result by forbid
ding a term to be diverted to another meaning in the
same discussion or discourse. While we are treating of
one subject, we must fix the meanings of our terms, and
keep to the same meanings.
(V) Just as the principle of Identity
declared that
all parts of truth must be self-consistent, so the principle
of non-contradiction declares that the different parts of
truth cannot be incompatible with one another. We may
illustrate this by referring to the manner in which certain
types of philosophical doctrine have been maintained.
1 The philosophical aspects of the Law of Identity will be further
considered in ch. XI. 8 2.