 Re: That or Which
The relative pronoun that is used to introduce restrictive relative clauses. That is, relative clauses that are essential to the meaning of the sentence. e.g. "...materials that are harmful..."
The relative pronoun which is used to introduce non-restrictive relative clauses. That is, relative clauses that are not essential to the meaning of a sentence and are set off by commas. e.g.
"Chemicals and other materials, which are very common, that are harmful..." |