One of the trickiest challenges we encounter when mastering English is navigating words that look almost identical but carry very different grammatical weights. The “Which” and “That” duo is undoubtedly at the top of this list. While they might seem completely interchangeable at first glance, using the wrong one can alter the structure—and sometimes even the meaning—of your sentence. In this article, we will break down the rules, key differences, and everyday usages of these two words in the simplest way possible to clear up all your doubts once and for all.
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What Are “Which” and “That” in English?
Both “Which” and “That” are called Relative Pronouns in English. Their job is to connect two different sentences or ideas and to give more information about an object, animal, or situation. The basic logic is that both words modify the noun in front of them. However, the crucial question here is: Is the information we provide essential for the meaning of the sentence, or is it just extra detail? The whole distinction lies in the answer to this question!
When to Use “Which”?
“Which” is used when giving extra, non-essential (non-defining) information about the noun it modifies—meaning the main point of the sentence remains intact even if this information is removed. It is preferred only for objects and animals (we use “who” for people).
The biggest clue is this:
- If you are using “which,” you usually need to put a comma (,) before it.
- When you remove that part from the sentence, the main idea of the sentence is still fully understood.
Example: My car, which is red, is parked outside.
The “which is red” part here is extra information. Even if we say “My car is parked outside,” the main meaning of the sentence is not lost.
When to Use “That”?
“That” is used when giving essential, meaning-defining (defining) information about the noun it modifies. If you remove that information from the sentence, the listener cannot fully understand which object you are talking about.
The most important rule:
- A comma is never used before the word “that.”
Example: The car that I bought yesterday broke down.
Here, the “that I bought yesterday” part is essential information. If we only say “The car broke down,” the other person will ask, “Which car?” Since the information is mandatory, we used “that.”
Differences Between “Which” and “That”
| Feature | That | Which |
|---|---|---|
| Information Type | Essential / Mandatory Information | Extra / Optional Information |
| Comma Usage | No comma is used before it | A comma is used before it |
| If Removed from Sentence | The sentence meaning breaks down or becomes unclear | The main meaning of the sentence does not change |
| Example | The book that you gave me was great. | The book, which is on the desk, is great. |
Frequently Asked Questions About Using Which and That in English
Let’s take a look at the frequently asked questions about differences between these two conjunctions.
Why is the comma rule so important?
The comma indicates whether the information is “extra” or not. Since the information provided by “which” does not change the core message of the sentence, it is preceded by a comma. On the other hand, “that” carries the main meaning of the sentence, so it is never separated by a comma.
Can “That” be used when talking about people?
In daily spoken language, “that” is often preferred instead of “who” for people (e.g., The girl that lives next door). However, in formal and academic writing, it is best to use only “who” for people.
Is there a difference between American and British English regarding this topic?
Yes. American English applies the rule very strictly (that= essential information, which= extra information). In British English, however, using “which” without a comma is quite common, even in essential/defining sentences.
Can we completely omit the words “Which” or “That” when forming a sentence?
If a new subject directly follows these words (meaning they are in the object position), you can completely remove both of them from the sentence. For example: instead of The book that you bought…, you can directly say The book you bought….
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