The Oxbridge Editing Blog 3rd April 2024

Which vs That: Understanding the Difference

3rd April 2024
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In English, there are subtle nuances that often dictate the choice of words. One such pair of words that frequently causes confusion is “which” and “that.” Despite their apparent similarity, these words serve distinct purposes in sentence structure. Knowing when to use “which” or “that” is crucial for clear communication. But remember, there are differences in how they’re used in British English and American English. Read on to learn more about their usage.

The Grammatical Difference Between Which and That

“Which” and “that” are both relative pronouns used to introduce subordinate clauses within a sentence. However, their usage varies based on whether the clause they introduce is essential or non-essential to the meaning of the sentence.

Using “Which”

“Which” is typically used to introduce non-essential or non-restrictive clauses. These clauses provide additional information about a noun but are not essential for understanding the main point of the sentence. Non-essential clauses introduced by “which” are set off by commas.

For example:

“The book, which was published last year, has become a bestseller.”

“She bought a new car, which she had been saving up for.”

In these examples, the clauses introduced by “which” provide additional details about the noun (“the book” and “a new car”), but the sentences would still be grammatically correct and meaningful without them.

Using “That”

In American English “that” is used to introduce essential or restrictive clauses. These clauses are crucial for understanding the meaning of the sentence, and omitting them would alter the intended message. Essential clauses introduced by “that” are not set off by commas.

For example:

“The book that she recommended is out of stock.”

“I need the keys that you borrowed yesterday.”

In these sentences, the clauses introduced by “that” are essential for identifying which book is out of stock and which keys are needed.

Which vs That: British English vs American English

The rules outlined above form the foundation of formal American English. However, in British English (and generally in spoken English) this distinction isn’t as rigorously followed. In British English, you actually have the freedom to interchange “which” or “that” for the restrictive clause without changing the meaning. Yet, in American English, “which” is exclusively reserved for non-restrictive clauses.

British English:

Restrictive clause: “The car which/that is parked outside belongs to Tom.”

  • (Both “which” and “that” are acceptable in British English for the restrictive clause.)

American English:

Restrictive clause: “The car that is parked outside belongs to Tom.”

  • (“That” is preferred in American English for the restrictive clause.)

Non-restrictive clause: “My car, which is parked outside, belongs to Tom.”

  • (“Which” is used exclusively for non-restrictive clauses in American English.)

Tricks to Remember When to Use “Which” or “That”

Here are a few tips that can help you master their usage with confidence, especially if you decide to follow the American English conventions:

Identify Essential vs. Non-essential Clauses: Before deciding whether to use “which” or “that,” determine whether the clause you’re introducing is essential or non-essential to the meaning of the sentence. 

Punctuation: Pay attention to punctuation cues. Non-essential clauses introduced by “which” are set off by commas, whereas essential clauses introduced by “that” are not. This distinction helps clarify whether the information provided by the clause is essential or supplementary.

Test for Essentiality: To determine whether a clause is essential, try omitting it from the sentence and see if the main message remains clear. If the omission significantly alters the meaning or leaves the sentence ambiguous, the clause is likely essential and, if you adhere to American English conventions, it should be introduced by “that.”


Understanding the grammatical differences and knowing when to use “which” or “that” based on the essentiality of the clause is crucial. While British English offers more flexibility in the use of these relative pronouns, American English adheres more strictly to distinct rules regarding their usage. 

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