e attributes which we associate with that class. So long, therefore,
as the word fish means to us an animal living in the water, we will
include in the class the whale, which really does not belong to the
class, and perhaps exclude from the class the flying fish, although it
is scientifically a member of the class.

THE DEFINITION

It has been noted that, when man discovers common characteristics in a
number of objects, he tends on this basis to unite such objects into a
class. It is to be noted in addition, however, that in the same manner
he is also able, by examining the characteristics of a large class of
objects, to divide these into smaller sub-classes. Although, for
example, we may place all three-sided figures into one class and call
them triangles, we are further able to divide these into three
sub-classes owing to certain differences that may be noted among them.
Thus an important fact regarding classification is that while a class
may possess some common quality or qualities, yet its members may be
further divided into sub-classes and each of these smaller classes
distinguished from the others by points of difference. Owing to this
fact, there are two important elements entering into a scientific
knowledge of any class, first, to know of what larger class it forms a
part, and secondly, to know what characteristics distinguish it from the
other classes which go with it to make up this larger class. To know the
class equilateral triangle, for instance, we must know, first, that it
belongs to the larger class triangle, and secondly, that it differs from
other classes of triangles by having its three sides equal. For this
reason a person is able to know a class scientifically without knowing
all of its common characteristics. For instance, the large class of
objects known as words is subdivided into smaller classes known as parts
of speech. Taking one of these classes, the verb, we find that all verbs
agree in possessing at least three common characteristics, they have
power to assert, to denote manner, and to express time. To distinguish
the verb, however, it is necessary to note only that it is a word used
to assert, since this is the only characteristic which distinguishes it
from the other classes of words. When, therefore, we describe any class
of objects by first naming the larger class to which it belongs, and
then stating the characteristics which distinguish it from the other
co-ordinate classes, we a