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

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DEFINITION.
A scientific system of classification is the grouping of
classes in such an order as will lead to the discovery of
their affinities,
the relations in which the real structure,
typical of each class, stands to that of the others. Its
result is that the classes thus formed correspond to
what appears to be the great divisions of nature. It
has also been called "classification by series." This is
illustrated, both on a great scale and a small, in the
classifications of natural history Zoology, Botany,
Crystallography, Mineralogy, &c.
The natural classification is not appropriate for all
purposes,
even in science. We have seen that it takes
as a basis the most fundamental properties, those
which have a determining effect on the largest number
of others. Sometimes
"
the test of importance in an
attribute proposed as a basis of classification is the
number of others of which it is an index or invariable
accompaniment," while the latter are not its conse
quences or effects, and may not be in any important
respect affected by it. "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 hedgehog, the shrew-
mouse, and the mole, though very unlike in outward
appearance and habits, are classed together as Insecti-
vora, the difference in what they feed on being accom
"
panied by a number of other differences (Minto, Logic,
p. 98). Again, certain characters in natural objects may
be comparatively of no importance, but may be invari
ably present and very easily recognised ; in such cases,
it is practically convenient, in scientific work,
these as a basis of division.
to take