Sciences, of animals, plants, and stones, with a view to
the thorough study of them in form, structure, and function, is
more complex than classifications for more limited purposes, and the
tendency is to restrict the word classification to these elaborate
systems. But really they are only a series of divisions and
subdivisions, and the same principles apply to each of the subordinate
divisions as well as to the division of the whole department of study.

II.--PRINCIPLES OF DIVISION OR CLASSIFICATION AND DEFINITION.

Confusion in the boundaries of names arises from confused ideas
regarding the resemblances and differences of things. As a protective
against this confusion, things must be clearly distinguished in their
points of likeness and difference, and this leads to their arrangement
in systems, that is, to division and classification. A name is not
secure against variation until it has a distinct place in such a
system as a symbol for clearly distinguished attributes. Nor must we
forget, further, that systems have their day, that the best system
attainable is only temporary, and may have to be recast to correspond
with changes of things and of man's way of looking at them.

The leading principles of DIVISION may be stated as follows:--

I. Every division is made on the ground of differences in
some attribute common to all the members of the whole to be
divided.

This is merely a way of stating what a logical division is. It is
a division of a generic whole or _genus_, an indefinite number of
objects thought of together as possessing some common character or
attribute. All have this attribute, which is technically called the
_fundamentum divisionis_, or generic attribute. But the whole is
divisible into smaller groups (_species_), each of which possesses the
common character with a difference (_differentia_). Thus, mankind may
be divided into White men, Black men, Yellow men, on ground of the
differences in the colour of their skins: all have skins of some
colour: this is the _fundamentum divisionis_: but each subdivision or
species has a different colour: this is the _differentia_. Rectilineal
figures are divided into triangles, quadrangles, pentagons, etc., on
the ground of differences in the number of angles.

Unless there is a _fund. div._, _i.e._, unless the differences are
differences in a common character, the division is not a logical
division. To divide men into Europeans, opticians, tail