How should we use “that” or “which” in a sentence?
Although these two words are often used interchangeably, there are situations where one or the other should be used. Here are two examples:-
1. The book that I’m reading now is very interesting.
2. That book, which has a red cover, is the one I’m reading now.
The difference is whether the clause is restrictive or non-restrictive.
“That” should be used in restrictive clauses, where the information is essential to the sentence’s meaning. The clause “that I’m reading now” is needed, otherwise we don’t know which book is interesting. Removing it would change the sentence’s meaning.
On the other hand, ‘which’ should be used in non-restrictive clauses, where the information, which is not essential to the meaning of the sentence, is set off by commas. The clause “which has a red cover” adds extra, but non-essential information about the book I’m pointing to.
A simple way to remember this rule is “that’s essential.” If the information is essential to the meaning of the sentence then use “that”, otherwise use “which”.
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