Relative clauses provide us with information about the subject or the object of a main clause. Among them, we can identify two types: defining and non-defining.
Defining relative clauses describe which person or thing we are talking about. For example, “George Lucas is the man who created Star Wars”.
Relative clauses are introduced by relative pronouns, such as who to talk about people, which to talk about things or animals, that to talk about things, animals and people (we can use it instead of who or which in defining relative clauses) and whose to talk about possesion (although it is considered a bit formal).
We can also use when to introduce a clause about time, days, years, etc, where to talk about places and why to talk about reasons.
Non-defining relative clauses do not describe who or what we are talking about, but they give us extra information about the object or the subject of the main clause and are used between commas, usually immediately after the subject or object it describes. For example, “George Lucas, who had just started making movies, became a very successful director after Star Wars».
We can also use non-defining relative clauses, usually at the end of the sentence, to say something about the whole of the main clause. For example, “Star Wars was an instant hit, which meant that George Lucas became a household name”.
