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name can be predicated of a definition: and, strictly speaking, it is
only in relation to a definition (as subject) that species can be a
predicable; when it is called _Species predicabilis_ (1).

If X be a connotative name, it is itself a species (_Species
subjicibilis_); and the place of the subject of a proposition is the
usual one for species. The predicate, Y, may then be related to the
species in three different ways. First, it may be a definition, exactly
equivalent to the species;--in fact, nothing else than the species in an
explicit form, the analysis of its connotation. Secondly, the predicate
may be, or connote, some _part only_ of the definition or connotation of
the species; and then it is either genus (2), or difference (3).
Thirdly, the predicate may connote _no part_ of the definition, and then
it is either derivable from it, being a proprium (4), or not derivable
from it, being an accident (5). These points of doctrine will be
expanded and illustrated in subsequent pages.

If X be a singular name, deriving connotation from its constituent terms
(chap. iv. Sec. 2), as 'The present Emperor of China,' it may be treated as
a _Species subjicibilis_. Then that he is 'an absolute monarch,'
predicates a genus; because that is a genus of 'Emperor,' a part of the
singular name that gives it connotation. That he wears a yellow robe is
a proprium, derivable from the ceremonial of his court. That he is
thirty years of age is an accident.

But if X be a proper name, having no connotation, Y must always be an
accident; since there can then be no definition of X, and therefore
neither species, genus, difference, nor proprium. Hence, that 'John Doe
is a man' is an accidental proposition: 'man' is not here a _Species
predicabilis_; for the name might have been given to a dog or a
mountain. That is what enables the proposition to convey information: it
would be useless if the proper name implied 'humanity.'

'Species' is most frequently used (as in Zoology) for the _class
denoted_ by a general name; but in Logic it is better to treat it as a
general name used connotatively for the attributes possessed in common
by the things denoted, and on account of which they are regarded as a
class: it is sometimes called the Essence (Sec. 9). In this connotative
sense, a species is implicitly what the definition is explicitly; and
therefore the two are always simply convertible. Thus, 'A plane
triangle' (species) is 'a figure