g and
become ambiguous. Throughout most of its uses it retains this much of
a common signification, the fixing or determining of the boundaries
of a class[3] by making clear its constituent attributes. Now in this
making clear two processes may be distinguished, a material process
and a verbal process. We have (1) the clearing up of the common
attributes by a careful examination of the objects included in the
class: and we have (2) the statement of these common attributes in
language. The rules of definition given by Dr. Bain, who devotes a
separate Book in his Logic to the subject of Definition, concern the
first of these processes: the rules more commonly given concern mainly
the second.

One eminent merit in Dr. Bain's treatment is that it recognises the
close connexion between Definition and Classification. His cardinal
rules are reduced to two.

I. _Assemble for comparison representative individuals of the
class._

II. _Assemble for comparison representative individuals of the
contrasted class or classes._

Seeing that the contrasted classes are contrasted on some basis of
division, this is in effect to recognise that you cannot clearly
define any class except in a scheme of classification. You must have
a wide _genus_ with its _fundamentum divisionis_, and, within this,
_species_ distinguished by their several _differentiae_.

Next, as to the verbal process, rules are commonly laid down mostly
of a trifling and obvious character. That "a definition should state
neither more nor less than the common attributes of the class," or
than the attributes signified by the class-name, is sometimes given
as a rule of definition. This is really an explanation of what a
definition is, a definition of a definition. And as far as mere
statement goes it is not strictly accurate, for when the attributes
of a genus are known it is not necessary to give all the attributes of
the species, which include the generic attributes as well, but it is
sufficient to give the generic name and the differentia. Thus
Poetry may be defined as "a Fine Art having metrical language as its
instrument". This is technically known as definition _per genus
et differentiam_. This mode of statement is a recognition of the
connexion between Definition and Division.

The rule that "a definition should not be a synonymous repetition of
the name of the class to be defined," is too obvious to require formal
statement. To describe a Vicer