Relative Clauses
From TEFL World Wiki
A relative or adjectival clause gives information about a noun and functions as an adjective. It is a dependent clause and as such it cannot stand alone as a sentence.
A relative clause consists of a relative pronoun (or adverb), a subject and a verb.
relative pronoun or adverb + subject + verb
For the party we bought several bottles of spirits, which nobody drank.
Or it can just have a relative pronoun functioning as a subject, and a verb.
relative pronoun (as subject) + verb
The law that the senate passed disappointed many citizens.
Relative Clauses & Punctuation
When a relative clause provides information that are necessary to the understanding of the full meaning of a sentence then no commas are required.
We can donate to the Library the books which are on the top shelf.
When a relative clause provides information that are not necessary to the understanding of the full meaning of a sentence then commas can be placed.
We can donate to the Library the English grammar books, which are on the top shelf.
See Also
A Curious Visitor - an activity to practice relative clauses with your class
