“Which” and “that” are a lot like identical twins, in that they’re pretty easy to mix up at first glance. But just like identical twins have unique traits that set them apart, so do these similar yet distinct terms. One reason we mix up “which” and “that” so often is the words were used interchangeably until the 1700s, and old habits die hard. But under today’s grammatical guidelines, there’s an appropriate context for “which,” and separate occasions for “that.”
Both “which” and “that” are relative pronouns, meaning they can refer to any related or previously mentioned nouns. But to understand how they differ, it’s useful to define the concepts of restrictive and nonrestrictive clauses. A restrictive clause adds essential information to a sentence: “The album that came out after her child was born changed her musical style.” In this example, the restrictive clause of “that came out after her child was born” is crucial to the meaning of this sentence.
A nonrestrictive clause, however, works as a conversational aside, adding nonessential information: “The band’s first album, which was my favorite, had great backup singers.” It might be nice to know that you like an album, but the point of this sentence is the prowess of the backup singers, so the clause within the commas is considered nonrestrictive. As these examples show, it’s appropriate to use “that” in restrictive clauses, and “which” in nonrestrictive clauses.
Nonrestrictive clauses often appear at the end of sentences, not just in the middle like in our example above. For example, “David Bowie’s album Young Americans had famous backup singers, which included Luther Vandross.” Here’s our memory tip: If you need a comma, you’re probably dealing with a nonrestrictive clause, meaning “which” is almost always the correct choice. Commas set off info that, when removed, doesn’t impact the sentence’s clarity or meaning. If you don’t need a comma, use “that.”
“That” has a variety of usages “which” cannot serve. It can act as a definite article referring to a specific noun (“That is my favorite album”), as a conjunction to connect two clauses (“I didn’t know that it was their first time performing together”), or as an adverb to add context before an adjective or verb (“I don’t want to spend that much money on concert tickets”). This makes “that” more versatile than “which.”
