In everyday conversation, people use that and which interchangeably without giving the words much thought. However, when using them as relative pronouns to introduce adjective clauses, the choice of using that or which determines the meaning of a sentence. It’s another grammar rule that is more important in writing than it is in speech.
So, how do you know which word to use? Simply put, use that before a restrictive clause and which before a nonrestrictive clause. Easy enough, right?
Restrictive (or essential) clauses limit the meaning of the nouns they modify. They add important information, and leaving it out would change the sentence’s meaning.
Example: The bacon cheeseburgers that are topped with cheddar sell fast.
In this sentence, we specifically know the bacon cheeseburgers with cheddar sell fast. We don’t know anything about the burgers with a different cheese.
Nonrestrictive (or nonessential) clauses simply provide additional information that can be left out of a sentence without changing its meaning.
Example: The bacon cheeseburgers, which are topped with cheddar, sell fast.
In this sentence, we can assume cheddar is on every bacon cheeseburger and they all sell fast.
Did you notice the commas in the nonrestrictive clause example and how they are absent in the restrictive clause example. The rule of thumb is to surround a nonrestrictive clause with commas. If the sentence ends in a nonrestrictive clause, set it off with a single comma. For example, “I ate a bacon cheeseburger for lunch, which was delicious.”
Would you like us to explore other grammar questions? Let us know in the comments.