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

l82 DEFINITION.
that of "Inductive" Logic, as Jevons and Fowler do. But
there is no reason for this separation. "Division" tends to
signify the splitting up of a given class into sub-classes ;
"Classification," the systematic arrangement of animals, of
plants, of minerals, &c, in Science, for the sake of studying
their form, structure, and function. We shall consider the
latter process first.
The fundamental rule is that objects are classed
together when they resemble one another in a definite
quality or group of qualities. But to define a class as
an arrangement of objects according to their common
qualities, is a definition which errs by being too wide,
inasmuch as it would include as
"
"
classes combinations
which we never form, and which we should regard as
almost absurd. Compare, for example, the two follow
(a) The classing together of various
human beings (negroes, Europeans, Hindoos, &c.) as
ing combinations :
having in common the attributes of manhood; (^) the
classing together of negroes, coal, and black chalk as
being all black, solid, extended, divisible, heavy. If the
which is based on classification consisted of
concept
any collection of common qualities, (ff) would have to be
"
considered as a "class
\
but the mind has not naturally
formed such a concept, and never would deliberately
form it. On the other hand (a) is a type of the
universals which we form both consciously and uncon
sciously. The difference is that in () the common
qualities on which the stress is laid are those which we
have called
"
essential," those qualities which have a
determining influence on the largest number of the
others.
8. We have seen, then, that the attribute or group of
attributes, in virtue of which we form objects into a class,
must consist of the common qualities which are essential.
Since these are the characters that carry with them