An essential relative clause provides necessary, defining information about the noun. On the other hand, non‐ essential relative clauses provide additional, non‐necessary information about the noun.

Relative clauses are used to give additional information about a noun, such as a person, place or thing. Relative pronouns introduce a relative clause. They include who for people, that and which for ...

In this paper, the syntactic differences exhibited by English restrictive relative clauses vs. non-restrictive or appositive ones are accounted for by positing that restrictive operators move to C° ...