one
division, may be important enough to be the basis of another division.
Thus in a division of houses according to their architectural
attributes, the number of windows or the rent is of little importance;
but if houses are taxed or rated according to the number of windows
or the rent, these attributes become important enough to be a basis
of division for purposes of taxation or rating. They then admit of
important differences.

That the importance is relative to the purpose of the division should
be borne in mind because there is a tendency to regard attributes that
are of importance in any familiar or pre-eminent division as if they
had an absolute importance. In short, disregard of this relativity is
a fallacy to be guarded against.

In the sciences, the purpose being the attainment and preservation
of knowledge, the objects of study are divided so as to serve that
purpose. Groups must be formed so as to bring together the objects
that have most in common. The question, Who are to be placed together?
in any arrangement for purposes of study, receives the same answer
for individuals and for classes that have to be grouped into higher
classes, namely, Those that have most in common. This is what Dr. Bain
happily calls "the golden rule" of scientific classification: "Of the
various groupings of resembling things, preference is given to such as
have the greatest number of attributes in common". I slightly
modify Dr. Bain's statement: he says "the most numerous and the most
important attributes in common". But for scientific purposes number of
attributes constitutes importance, as is well recognised by Dr. Fowler
when he says that the test of importance in an attribute proposed as a
basis of classification is the number of other attributes of which it
is an index or invariable accompaniment. Thus in Zoology the
squirrel, the rat, and the beaver are classed together as Rodents, the
difference between their teeth and the teeth of other Mammalia being
the basis of division, because the difference in teeth is accompanied
by differences in many other properties. So the hedge-hog, the
shrew-mouse, and the mole, though very unlike in outward appearance
and habits, are classed together as Insectivora, the difference in
what they feed on being accompanied by a number of other differences.

_The Principles of_ DEFINITION. The word "definition" as used in Logic
shows the usual tendency of words to wander from a strict meanin