An extensional definition assigns meaning to a term by indicating the members of the…

An extensional definition assigns meaning to a term by indicating the members of the class that the term denotes. A definition by subclass is a type of extensional definition that assigns meaning to a term by naming subclasses of the class that the term denotes. A definition by subclass is complete if the subclasses named, when taken together, include all members of the class that the definiendum denotes. A definition by subclass is partial if the subclasses mentioned, when taken together, do not include all members of the class that the definiendum denotes. The things named in a definition by subclass are smaller classes of the items within the larger class; they are not the individual members of the larger class themselves. This is what differentiates a definition by subclass from an enumerative definition.
Indicate whether each of the following definitions is a complete definition by subclass, is a partial definition by subclass, or is not a definition by subclass.
Definition A
“Mammal” means something such as a dolphin, a hamster, an otter, a fox, or a cheetah.
Definition A is definition by subclass.
Definition B
“Airplane” means something such as the Spirit of St. Louis, the Enola Gay, the Memphis Belle, or the Cruisin’ Susan.
Definition B is definition by subclass.
Definition C
“Real number” means either a rational number or an irrational number.
Definition C is definition by subclass.
Definition D
“Ship” means a vessel such as the USS Enterprise, USS John F. Kennedy, or the USS Constitution.
Definition D is definition by subclass.