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

44
THE NAME, THE TERM, THE CONCEPT,
degree of heat is signified by that word. And in the
case of the great divisions of Nature, which seem to
shade off into one another, as "animal" into "veget
able," and "vegetable" into "inanimate
matter,"
may be in doubt as to the application of the law of
excluded middle to an individual on the borderline of
one of these divisions ; we may not be able to say
either that it is an animal or that it is not an animal,
it may seem to be something between the two. But
this results from our imperfect understanding of what
animal life really is ; the greater the light which is
thrown on this problem, the smaller the extent of the
doubtful borderland, of things which seem neither in the
class of
"
"
animal life nor outside it.
Sometimes the law of excluded middle has been
questioned through
we
a mere confusion. The contrast
which the law of thought makes, is between two pro
positions one of which simply
denies or contradicts
the other, between an affirmative and a negative pro
position, "This water is hot, this water is not hot,"
"
This paper is white, this paper is not white,"
"This line is longer than that, this line is not longer
than that," "This opinion is simply true [i.e., true with
out qualification or limitation], this opinion is simply
not true." In each of these pairs of propositions, one
and one only must be true ; there is no third alternative.
But it is not uncommon to apply the law to a pair
of propositions which affirm contrary predicates of an
object, and to say (taking the last of the above examples)
that "either this opinion is simply true or it is simply
false." Here there may be a third alternative, it may
be a mixture of truth and error.
"white" and "black,"
Similarly, between
"hot" and "cold," "greater
than," and "less
than," in each case there are other