Full Idea
The classical view of concepts explains hierarchical order, where categories form nested sets. But research shows that categories are often not transitive. Research shows that a seat is furniture, and a car seat is a seat, but it is not furniture.
Gist of Idea
Classical concepts are transitive hierarchies, but actual categories may be intransitive
Source
Gregory L. Murphy (The Big Book of Concepts [2004], Ch. 2)
Book Reference
Murphy,Gregory L.: 'The Big Book of Concepts' [MIT 2004], p.27
A Reaction
[compressed] Murphy adds that the nesting of definitions is classically used to match the nesting of hierarchies. This is a nice example of the neatness of the analytic philosopher breaking down when it meets the mess of the world.