It's the difference between a strict hierarchy and cross-cutting sets. Composition allows you to "talk about" a given category of which any set of objects can b

It's the difference between a strict hierarchy and cross-cutting sets. Composition allows you to "talk about" a given category of which any set of objects can be members, independently of their membership in other categories. Whereas with inheritance, if a member of category B wants to reuse aspects of category A, all B's must strictly be A's.