and induction, by the same method we discover the
definition of its name.

We saw also that classification is not merely the determination of
isolated groups of things, but a systematic arrangement of such groups
in relation to one another. Hence, again, Definitions are not
independent, but relative to one another; and, of course, in the same
way as classes are relative. That is to say, as a class is placed in
subordination to higher or more comprehensive groups, so the definition
of its name is subordinate to that of their names; and as a class stands
in contrast with co-ordinate classes (those that are in the same degree
of subordination to the same higher groups), so the definition of its
name is in contrast or co-ordination with the definitions of their
names. Lion is subordinate to _Felis_, to Digitigrade, to Carnivore and
so on up to Animal; and, beyond the Animal Kingdom, to Phenomenon; it is
co-ordinate with tiger, puma, etc.; and more remotely it is
co-ordinate with dog, jackal, wolf, which come under _Canis_--a genus
co-ordinate with _Felis_. The definition of lion, therefore, is
subordinate to that of _Felis_, and to all above it up to Phenomenon;
and is co-ordinate with that of tiger, and with all species in the same
grade. This is the ground of the old method of definition _per genus et
differentiam_.

The genus being the next class above any species, the _differentia_ or
Difference consists of the qualities which mark that species in addition
to those that mark the genus, and which therefore distinguish it from
all other species of the same genus. In the above definition of lion,
for example, all the properties down to "light and muscular in build"
are generic, that is, are possessed by the whole genus, _Felis_; and the
remaining four (size, colour, tufted tail, and mane in the male) are the
Difference or specific properties, because in those points the lion
contrasts with the other species of that genus. Differences may be
exhibited thus:

_Lion._ _Tiger._
SIZE: about 9-1/2 feet from nose | About 10 feet.
to tip of tail. |
COLOUR: tawny. | Warm tawny, striped with black.
TAIL: tufted. | Tapering.
MANE: present in the male. | Both sexes maneless.

There are other differences in the shape of the skull. In defining lion,
then, it would have been enough to mention the genus and the properties
makin