ns made. There are no triangles which are
neither right nor oblique, so the division is complete; and no triangle
can be both right and oblique, so the division is exact. Such a complete
and exact division is called _classification_.

Nearly every term may be divided according to more than one principle. We
may divide the term _books_ into ancient and modern, or into religious and
secular, or in any one of a dozen other ways. Which principle of division
we shall choose will depend upon our purpose. If we wish to discuss
_sponges_ with reference to their shapes, our division will be different
from what it would be if we were to discuss them with reference to their
uses. When a principle of division has once been chosen it is essential
that it be followed throughout. The use of two principles causes an
overlapping of divisions, thus producing what is called cross division.
Using the principle of use, a tailor may sort his bolts of cloth into
cloth for overcoats, cloth for suits, and cloth for trousers; using the
principle of weight, into heavy weight and light weight; or he may sort
them with reference to color or price. In any case but a single principle
is used. It would not do to divide them into cloth for suits, light weight
goods, and brown cloth. Such a division would be neither complete nor
exact; for some of the cloth would belong to none of the classes while
other pieces might properly be placed in all three.

In the exact sciences complete exposition is the aim, and classification
is necessary; but in other writing the purpose in hand is often better
accomplished by omitting minor divisions. A writer of history might
consider the political growth, the wars, and the religion of a nation and
omit its domestic life and educational progress, especially if these did
not greatly influence the result that he wishes to make plain. If we
wished to explain the plan of the organization of a high school, it would
be satisfactory to divide the pupils into freshmen, sophomores, juniors,
and seniors, even though, in any particular school, there might be a few
special and irregular pupils who belonged to none of these classes.
An exposition of the use of hammers would omit many occasional and
unimportant uses. Such a classification though exact is incomplete and is
called _partition_.

EXERCISES

_A._ Can you tell which of the following are classifications? Which are
partitions? Which are defective?

1. The inhabitan