already defined or perfectly understood. It should not be
in negative form where it can be affirmative. If the class of objects
has a peculiar property, the naming of that may serve as a definition.
If no peculiar property can be detected, the definition should name more
than one quality or property. Several different classes may have one or
more properties alike, but as the number is increased the likelihood of
there being others having the same properties is decreased. The briefest
possible statement of such properties or qualities as are possessed by
all the objects of a class and not completely possessed by any other
objects, which will suffice to distinguish the class from other classes
and determine its position in the general classification, will be most
satisfactory. To define any species, the genus having been defined, the
genus should be named and the difference added. Of course, no generic
definition should contain any limitation not characteristic of every
species of the defined genus. In seeking qualities by which to describe
a genus or species, no accident should be selected.

Example: Suppose there be marked out and defined as a genus
all means whereby one form of energy is transformed into
another form of energy and no more, and the genus be named
energy-transformers. We may then name, as species,
energy-transformers that are motors and energy-transformers
that are not motors. Motors may be defined by merely naming
the genus energy-transformers, and stating the difference,
to wit, continuously transforming energy into cyclical
mechanical motion. Then the definition will be:
Energy-transformers that are adapted to continuously
transform energy into cyclical mechanical motion. The
non-motor division will retain the genus definition.

It would not be illuminating for a searcher having little
familiarity with the textile arts to look under the title
"Carding" and find that carding is defined as a means for
carding fiber.

Even though the first steam-engine invented had been used
to run a gristmill, the accident of its use as a part of a
gristmill would hardly warrant the definition of a
steam-engine as a means to grind corn. Nor would a hammer
be properly defined as an instrument to drive nails or to
crack nuts or to forge horseshoes, even though a patent
should not mention any use other than one of these and
should lay heavy emphas