Genus–differentia definition

A genus–differentia definition is a type of intensional definition, and it is composed of two parts:

  1. 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.
  2. the differentia: The portion of the definition that is not provided by the genus.

For example, consider these two definitions:

  • a triangle: A plane figure that has 3 straight bounding sides.
  • a quadrilateral: A plane figure that has 4 straight bounding sides.

Those definitions can be expressed as one genus and two differentiae:

  1. one genus:
    • the genus for both a triangle and a quadrilateral: "A plane figure"
  2. two differentiae:
    • the differentia for a triangle: "that has 3 straight bounding sides."
    • the differentia for a quadrilateral: "that has 4 straight bounding sides."

The use of a genus (Greek: genos) and a differentia (Greek: diaphora) in constructing a definition goes back at least as far as Aristotle (384–322 BCE). Furthermore, a genus may fulfill certain characteristics (described below) that qualify it to be referred to as a species, a term derived from the Greek word eidos, which means "form" in Plato's dialogues but should be taken to mean "species" in Aristotle's corpus.

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.