When to use that
“That” is used to introduce restrictive clausesA restrictive clause is essential to the meaning of the sentence. It defines or identifies the noun it modifies, and without it, the sentence would lose its intended meaning. Restrictive clauses are not set off by commas., also known as essential clauses. These clauses provide crucial information that defines or limits the meaning of the sentence.
Examples:
“The book that I borrowed from the library is overdue.” (There are multiple books, and the phrase specifies which one is due.)
“Books that teach critical thinking are essential for high school students.” (In this context, the sentence is specifically talking about only those books that teach critical thinking.)
Tip: If removing the clause changes the sentence's meaning, use “that.”
When to use which
“Which” introduces non-restrictive clausesA non-restrictive clause provides extra, non-essential information about the noun. This information could be removed without changing the core meaning of the sentence. Non-restrictive clauses are set off by commas., also known as non-essential clauses. These clauses add extra information that isn’t necessary to understand the main point of the sentence.
Examples:
“The book, which I borrowed from the library, is overdue.” (There’s only one book in the context, and the fact that it came from the library is just extra info—making the sentence interesting but not really required.)
“Books, which are a great source of knowledge, can shape our thinking.” (The fact that books are a great source of knowledge is extra information and not essential to the sentence’s core meaning.)
Tip: “Which” clauses are often separated by commas.
Quick test
Choose the correct word (which or that) for each sentence:
The car _____ he bought last week is already having issues.