I’ve edited hundreds of books and documents, and one of the issues that drives writers crazy is trying to figure out when to use “that” or “which” when either is used to introduce a dependent clause that modifies a preceding noun or pronoun. (See that? I used “that.” An argument with a grammarian may now ensue.)
Nowadays, editors try to use “that” for what we call restrictive clauses. This means that the information provided by the clause is indispensable. Here is an easy example: “The car that gets the best gas mileage is the one I’ll buy.” The phrase about the gas mileage is necessary to the sentence. You cannot remove it.
Editors try to use “which” when the information is non-restrictive or incidental. You don’t need it to understand the central meaning of the sentence. Here is an example: “The car, which gets great gas mileage, is the one that I will buy.” The part about the gas mileage is additional information about the car, but it is not absolutely necessary.
Most editors will use a comma before “which,” as I did in the preceding example. Editors will not use a comma preceding “that.”
Here is a trickier example: “I will buy the car which gets the best gas mileage.” If you put a comma in front of “which,” it looks wrong: “I will buy the car, which gets the best gas mileage.” A grammarian might insist that the sentence read, “I will buy the car that gets the best gas mileage.” This sentence suggests that there are a finite number of cars from which to choose – perhaps two or three.
Sometimes, to break a tie, I will check to see if the preceding noun is identified by “a” or “the.” If the sentence talks about “a car,” it is obviously one of many, and needs to be further identified. Here is an example: “A car that gets good gas mileage is inexpensive to operate.”
Contrast that with this example: “The car, which gets good gas mileage, is inexpensive to operate.” When you say “the car,” you have identified only one car, and so the information about the gas mileage could be omitted.
When you have written a book or report, it’s important to make sure that the grammar is perfect – or at least within the limits that grammarians argue about! At Thomas Hauck book editing, my goal is to bring your book to the highest level possible. Every year in the United States almost a million new books are published, both by traditional publishers and self-publishers. It’s a very competitive marketplace, and books that contain basic errors are quickly set aside. You need to let your ideas shine through, and the only way to do that is with the assistance of a qualified book editor.
Contact Thomas Hauck, freelance book editor, for a free quote and unmatched personal service. I’m located in Gloucester, MA, USA, and I serve clients throughout the United States and around the world. Let’s get your book looking great!