Hi, I'm Ray Evans. I'm a certified copyeditor and proofreader.
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The next grammar issue that pops up a lot is "which" and "that."
These two little words are often used interchangeably, but there is actually a subtle difference in their
usage: "that" is used to introduce a restrictive clause, while "which" is used for non-restrictive clauses.
A restrictive clause is essential to the meaning of the sentence and without it the sentence would not
make sense. It provides information that is necessary to identify the noun it modifies.
The book, which I read last night, was amazing."
In this sentence ☝️, the clause "which I read last night" is not essential to understanding which book
is being referred to, but it provides additional information about when and how the book was read.
On the other hand, a non-restrictive clause provides additional information that is
not essential to the meaning of the sentence.
In a non-restrictive clause, "which" should be used instead of "that."
Now, let's look at an example of each type of clause:
Restrictive clause: "The car that I bought last week is already in the shop."
In this sentence, the clause "that I bought last week" is essential to identifying
which car is being referred to.
Non-restrictive clause: "My dog, which is a golden retriever, loves to sleep in my bed."
In this sentence, the clause "which is a golden retriever" provides additional information
about the speaker's dog, but is not essential to understanding which dog is being referred to.