Restrictiveness

In semantics, a modifier is said to be restrictive (or defining) if it restricts the reference of its head. For example, in "the red car is fancier than the blue one", red and blue are restrictive, because they restrict which cars car and one are referring to. ("The car is fancier than the one" would make little sense.) By contrast, in "John's beautiful mother", beautiful is non-restrictive; "John's mother" identifies her sufficiently, while "beautiful" only serves to add more information.