Relative clauses

A relative clause adds information about a noun by embedding a clause directly inside a sentence, instead of stating it separately.

I have a friend. She lives in Canada. → I have a friend who lives in Canada.

The relative clause (who lives in Canada) attaches to the noun it describes (a friend), letting English combine two ideas into one, more efficient sentence.

Relative clauses fall into two types, depending on how essential the information is:

• Defining relative clauses — provide essential information needed to identify exactly which person or thing is being talked about. Without this clause, the sentence would be unclear or incomplete.
  The book that I borrowed is missing. (which book? — the one I borrowed)

• Non-defining relative clauses — add extra, non-essential information about someone or something already clearly identified. The sentence would still make complete sense without it.
  My car, which I bought last year, has already broken down. (we already know which car — "my car")

This distinction affects not just meaning, but also punctuation and which relative pronouns can be used — which is exactly what we'll explore next.