Editing Definition (section)

===Classes of intensional definitions===
{{Main|Genus–differentia definition}}
A ''genus–differentia definition'' is a type of [[intensional definition]] that takes a large category (the ''genus'') and narrows it down to a smaller category by a distinguishing characteristic (i.e. the ''differentia'').<ref>Bussler, Christoph, and Dieter Fensel, eds. Artificial Intelligence: Methodology, Systems and Applications: 11th International Conference, AIMSA 2004: Proceedings. Springer-Verlag, 2004. p.6</ref>

More formally, a genus–differentia definition consists of:
* ''a [[genus]]'' (or family): An existing definition that serves as a portion of the new definition; all definitions with the same genus are considered members of that genus.
* ''the differentia'': The portion of the new definition that is not provided by the genus.<ref name=":0" />

For example, consider the following genus–differentia definitions:
* ''a [[triangle]]'': A plane figure that has three straight bounding sides.
* ''a [[quadrilateral]]'': A plane figure that has four straight bounding sides.

Those definitions can be expressed as a genus ("a plane figure") and two ''differentiae'' ("that has three straight bounding sides" and "that has four straight bounding sides", respectively).

It is also possible to have two different genus–differentia definitions that describe the same term, especially when the term describes the overlap of two large categories. For instance, both of these genus–differentia definitions of "square" are equally acceptable:
* ''a square'': a [[rectangle]] that is a [[rhombus]].
* ''a square'': a [[rhombus]] that is a [[rectangle]].

Thus, a "square" is a member of both genera (the plural of ''genus''): the genus "rectangle" and the genus "rhombus".