Question: That was good stuff on the “that,” “who,” “whom” topic. How about a follow-up on the distinction between “that” and “which?” (Patti Hauck)
Answer: Thanks for writing in, Patti. Happy to oblige.
Much like the rule for choosing between “that” and “who/whom,” the “that/which” rule can be a simple one to master, once you get the hang of it.
As a pronoun, “that” is used to introduce restrictive clauses. These are clauses which are essential to the meaning of the sentence. For example: “The car that hasn’t moved in a month finally got towed.” Without “that” and its restrictive clause, we wouldn’t know which car got towed.
“Which,” as you may have guessed, is used to begin non-restrictive or parenthetical clauses. These are clauses which can be removed from the sentence without dramatically altering its meaning. For example: “My guitar, which is acoustic, is my favorite possession.” If we removed “which is acoustic” from the sentence, it would still convey the same message: I like my guitar.
Just to illustrate the distinction between “that” and “which, let’s look at the sentence another way. If I had said, “My guitar that is acoustic is my favorite possession,” there is the implication that I have other guitars which aren’t acoustic.
So there we go: “That” and “which” in a nutshell. If the clause is necessary to the sentence, we’re going with “that.” If not, “which” is our pronoun.