A Relative Clause (or Adjectival Clause as it’s sometimes known) gives information about a noun and at the same time, works like an adjective.

Take a look a this sentence:

For the party we bought several bottles of very cheap spirits.

The noun spirits has been modified by an adjective. Alternatively, we could use a complete clause:

For the party we bought several bottles of spirits which were very cheap.

This we have a relative clause:

which were very cheap

And as you’ll see, it’s also a subordinate clause (meaning it can’t stand alone as a sentence).

How to Build a Relative Clause

A relative clause consists of a relative pronoun (or adverb), a subject and a verb:

{relative pronoun or adverb} + {subject} + {verb}

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.

The law they + passed disappointed many citizens.

Relative Clauses & Punctuation

When a relative clause provides information which is 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 which is not necessary to the understanding of the full meaning of a sentence then commas can be placed.

We can donate to the Library the books, which are on the top shelf.

Useful Links

Clauses‏‎ in English Grammar – an introduction to different clauses

Sentences‏‎ in English Grammar – making sentences in English