y of
classification there must be a corresponding difficulty of definition.

It has been proposed in such cases to substitute a Type for a
Definition; to select some variety of a species, or species of a genus,
as exhibiting its character in an eminent degree, and to regard other
groups as belonging to the same species or genus, according as they
agree more with this type than with other types representing other
species or genera. But the selection of one group as typical implies a
recognition of its attributes as prevailing generally (though not
universally) throughout the species or genus; and to recognise these
attributes and yet refuse to enumerate them in a definition, seems to be
no great gain. To enumerate the attributes of the type as an Approximate
Definition of the species or genus, true of _most_ of the groups
constituting the species or genus, answers the same purpose, is more
explicit, and can mislead no one who really attends to the exposition.
An approximate definition is, indeed, less misleading than the
indication of a type; for the latter method seems to imply that the
group which is now typical has a greater permanence or reality than its
co-ordinate groups; whereas, for aught we know, one of the outside
varieties or species may even now be superseding and extinguishing it.
But the statement of a definition as approximate, is an honest
confession that both the definition and the classification are (like a
provisional hypothesis) merely the best account we can give of the
matter according to our present knowledge.

Sec. 7. The limits of Definition are twofold: (a) A name whose meaning
cannot be analysed cannot be defined. This limitation meets us only in
dealing with the names of the metaphysical parts or simple qualities of
objects under the second requisite of a Terminology. Resistance and
weight, colour and its modes, many names of sounds, tastes, smells, heat
and cold--in fact, whatever stands for an unanalysable perception,
cannot be made intelligible to any one who has not had experience of the
facts denoted; they cannot be defined, but only exemplified. A sort of
genetic definition may perhaps be attempted, as if we say that colour is
the special sensation of the cones of the retina, or that blue is the
sensation produced by a ray of light vibrating about 650,000,000,000,000
times a second; but such expressions can give no notion of our meaning
to a blind man, or to any one who has never seen a