Difference between ‘that’ and ‘which’

There is a subtle difference between the use of ‘that’ and ‘which’ in a sentence. A relative clause provides additional information about the noun it describes, but it may be considered relevant or irrelevant to the overall point of the sentence.

A restrictive relative clause which begins with ‘that’ is usually considered essential or restrictive. Here is an example:

• I enjoyed reading the novel that I borrowed from my professor.

In the above sentence the word ‘that’ is relative to ‘novel’. There are many novels but here the reference is to a particular novel. The relative clause beginning with ‘that’ is considered restrictive, since it is an essential piece of information that identifies the novel.

Relative clauses beginning with ‘which’ may contain non-essential information and would be considered non-restrictive. Here is an example:

• KCG College of Technology, which is on the Old Mahabalipuram Road, offers aeronautical engineering programme at the undergraduate level.

In the above sentence the clause ‘which is on the Old Mahabalipuram Road’ is separated by commas and the information where the college is not essential to the main idea of the sentence. Even if it is removed the sentence will make sense. In the above sentence, it is not possible to replace ‘which’ with ‘that’.

In short, whenever the information is essential to identifying the subject, the proper pronoun to use is that. If the information is not essential, or can be set apart with commas, then the pronoun which is more likely to be correct. If the meaning of the sentence would be lost without the information, then it is most likely restrictive and that would be the proper pronoun to use.