Although people use the words “that” and “which” every day, there’s a bit of confusion on how to do so properly. In American English, grammar rules are clear about the differences in their usage. This article aims to be equally clear in explanation.
The word that is one of the most common relative pronouns in American English. Relative pronouns (e.g. when, who, whomever, whose, whatever, etc.) are used to modify or define a phrase, word, or idea contained in the main clause. The word, phrase, or idea being defined is called the antecedent. A defining clause (i.e. restrictive clause, essential clause) provides additional information to the meaning of the sentence and begins with the term “that.” Take these sentences as examples:
My laptop that has my old files was stolen yesterday.
The Lord Commander’s army that has the bravest fighting men will win.
The first sentence tells the reader that the laptop being spoken about has old files. The laptop in question is distinguished from the speaker’s other laptops by its old files. If the clause “that has my old files” was removed, the sentence will no longer imply that the speaker has more than one laptop. More so, given that the reader is aware of this fact, it will be unclear which laptop was stolen.
Let’s apply another simple guideline to the other sentence. The phrase “that has the bravest fighting men” distinguishes the kind of army the speaker is referring to. If the phrase is removed, either the meaning of the whole sentence would change or it would lose sense altogether.
The word which is used to introduce a non-defining clause in any sentence. A non-defining clause (i.e. nonrestrictive or nonessential clause) does not limit or restrict the meaning a sentence. Although some important details may be lost if the non-defining clause is removed, the meaning of the sentence is still intact.
My laptop, which has my old files, was stolen yesterday.
The Lord Commander’s army, which has the bravest fighting men, will win.
In the first sentence, the old files serve as a simple description of the laptop that was stolen. The sentence does not imply that the speaker is referring to more than one one laptop.
Again, in the second example, the phrase “which has the bravest fighting men” is describing an army that would most likely win a battle. If the nonrestrictive phrase is removed, the sentence can still stand on its own. The sentence also retains it meaning. Thus, “which” is typically used to add more information and can be removed without altering the meaning of the sentence. It is also important to remember that a nonrestrictive phrase starts and ends with a comma.
That vs Which
So what’s the difference between “that” and “which”? Although both terms are technically relative pronouns, they have different usages. The word “that” is used in a restrictive clause which defines the subject of the sentence. In contrast, the word “which” introduces a nonrestrictive clause or phrase that describes or provides additional info about the subject of a sentence.
|Used in a restrictive clause||Used in a nonrestrictive clause|
|When removed, the sentence will lose meaning or sense||When removed, the sentence stands on its own and does not lose meaning|
Here’s a YouTube video about the correct usage of “that” and “which.”