So I was tutoring a student today and we got to a point where I noticed she needed to insert “that” into her sentence. After sitting for a few seconds, I realized I wasn’t sure WHY she needed to insert it. All I knew is that it had to be done. That being said, I thought it would be a great idea to do a Grammar Quick Fix about “that” and “which.” Not only will it help me, but hopefully it will help you too!
Before we get started…
…we need to discuss restrictive and non-restrictive clauses. I hate busting out grammar terms in these things, but you need to know in order to understand how that and which work.
A restrictive clause “restricts” or limits the meaning/identity of a subject. Unlike the non-restrictive clause, this one is not separated by commas.
A non-restrictive clause adds additional information about a subject, but isn’t necessary to the main idea of the sentence. It is separated from the sentence with commas.
Ok, now let’s start.
That has various functions, but today we’ll be discussing it in the sense of it setting up a restrictive clause. That always sets up a RESTRICTIVE clause, never a non-restrictive clause. As such, commas are not needed. When you use that in a sentence, it is being used in a way that the information is necessary to complete the sentence–remember, it restricts the subject in some way. Let’s look at some examples:
“The book that has Kurt Vonnegut’s signature is missing.”
“The cat that has gray fur is friendly.”
The reason you would use that in these cases is to single out the subject as an individual. In the example with the book, we are specifying that there is ONE book with Vonnegut’s signature and that it’s missing. In the cat example, there is ONE gray cat and it is friendly. It is not a book with Marion Zimmer Bradley’s signature and it is not an orange cat. They are specific. (We’ll look at these examples with which in a little bit.)
Which also has a couple functions but is used primarily as an adjective for setting up non-restrictive clauses. Which will always set up a non-restrictive clause, and commas should be put around the clause. The information in the clause is extraneous and can be removed from the sentence with it still making sense. Let’s make those that examples into which examples:
“The book, which has Kurt Vonnegut’s signature, is missing.”
“The cat, which has gray fur, is friendly.”
Notice that if we remove the material in red, the sentence is still complete. Let’s look at the first example. The non-restrictive clause sets up a situation where there are multiple books with Vonnegut’s signature–it’s just describing an attribute of the text. So let’s say you’re in a bookstore which has 5 books with different signatures. One of the books is missing–the only one with Vonnegut’s signature. You would use the restrictive clause for this case.
Let’s look at the cat example. If you’re at a breeder’s house, there may be multiple cats of with similar coloring. You would describe the cat with the non-restrictive clause. If you were at my house and talking about my one gray cat (Mishka! My Persian cat :-D), you would use the restrictive clause.
Use that for specific, restrictive clauses. Use which for additional information–aka non-restrictive clauses. Good luck!