Writing tip: "that" or "which"?
Writing a sentence involves using a combination of restrictive and non-restrictive clauses. Restrictive clauses are essential to the meaning of the sentence, whereas non-restrictive clauses contribute additional information. For example, in “the book by Jones that is red is my favourite”, the clause “that is red” is a restrictive clause because it identifies that the red book is the favourite amongst the books written by Jones. However, in “the book by Jones, which is red, is my favourite”, “which is red” is a non-restrictive clause because it adds additional, non-critical information to the description. The sentence could exist without the non-restrictive clause: “The book by Jones is my favourite”.
When you’re deciding whether to use “which” or “that” in your sentence, consider if you’re writing a restrictive or non-restrictive clause. Is the information that follows the "which" or "that" critical to the meaning of the sentence? If yes, use “that”; if not, use “which”. For more information, please refer to "Who or whom? That or which?" or the Grammar Girl's "Which versus that".
One final punctuation point: when placing a non-restrictive clause in a sentence, the clause should be contained by commas: “The book by Jones, which is red, is my favourite”. The commas at the beginning and end of the clause indicate where the non-restrictive clause starts and finishes, thereby alerting your reader to the essential/non-essential information in the sentence. For more information on punctuating sentences, please see punctuation.
Please contact the Writing Centre if you have any questions.
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