Features of the non-defining relative clause
Unlike defining (integrated) relative clauses, non-defining relative clauses are not embedded in the nominal group structure. Although they are marked as subordinate by a relativizer, they are parentheticals which have considerable semantic independence.
Prosodically, they don’t share the intonation contour of the matrix clause. Instead, they have their own intonation contour, which constitutes an independent information unit:
You had better buy Celtic, which has not passed its sell-by date.
They don’t identify one referent from other possible referents. The antecedent is already restricted and the clause is complete.
Consequently, unlike integrated relatives, non-defining relatives can have as antecedent a proper noun or name, as above, which identifies a particular person or persons, object(s) or institution(s). The pronouns used are who, whom, whose and which, rarely that:
I’ll give the CD to Ben, who likes music. (*that likes music)
The injured child was taken to Alder Hey Children’s Hospital, which is in Wavertree.
Semantically, the supplementive provides additional new information which is not essential, but may explain or elaborate on the content of the previous clause.
When placed medially, the non-restrictive relative is enclosed:
Plans for extending the John Lennon airport, which will cope with ten times the present air traffic, are now under way.
You would think that my dad, who is an international economist with the World Bank, would understand this. (All American Girl)
As it makes an independent statement, which is an extension of the already complete unit, non-defining relatives are increasingly found functioning as freestanding subordinate clauses, which may initiate a new paragraph in written discourse.
And into the room walked David, the President’s son.
Who also happened to be David from my drawing class with Susan Boone.
(All American Girl)
