From Word Genius
With so much of our communication happening over email, Slack, text, and social DMs, our writing tends to speak for us. Casual and abbreviated language flies off our fingertips, but incomplete or incoherent sentences can wreck a first impression, especially in professional settings. Take a common grammar issue, such as when to use “which” versus “that.” It’s hard to know when to use one or the other — in part because we used them interchangeably until the 1700s. Whether you’re writing an email or texting a friend, make sure you’re using the right one.
Is the Information Necessary?
“Which” and “that” are both relative pronouns, meaning they can refer to related or previously mentioned nouns. In order to understand what these two parts of speech have in common, let’s spell out the difference between a restrictive clause and a nonrestrictive clause.
A restrictive clause adds need-to-know information to a sentence; without that clause, the sentence may be incomplete or hard to understand.
Example: The album that came out after her child was born changed her musical style.
A nonrestrictive clause works like a conversational aside; you may be providing context or added information, but the sentence is still clear and complete without it.
Example: The band’s first album, which was my favorite, had great backup singers.
Part of the reason it feels so easy to mix up “which” and “that” when writing is because they both can convey important contextual information. “That” is most commonly used with a restrictive clause, while “which” is usually in non-restrictive clauses.
Writer’s tip: If you need a comma, “which” is almost always the appropriate choice. Commas set off information that, when removed, the sentence in which it appeared will still make sense.
Example: The band’s first album had great backup singers.
“That” as Alternate Parts of Speech
When used in restrictive and nonrestrictive clauses, “that” and “which” function as pronouns. But “that” especially can perform as other parts of speech in different sentence constructions.
“That” can be a determiner or definite article, which refers to a specific noun. (See how “which” needs the comma for the nonrestrictive clause in the previous sentence?)
Example: That is my favorite album of all time.
“That” could also work as a conjunction, connecting two clauses.
Example: I didn’t know that it was their first time performing together
Finally, “that” can be used as an adverb to add context before an adjective or verb.
Example: I don’t want to spend that much money on tickets.
When it comes to using “that” and “which” correctly, context is everything. Do you have to stick to all grammar rules? That’s up to you. Many grammar rules are worth breaking — as long as you realize when you’re breaking them.