Learn the important distinction between “that” vs. “which” on GMAT Sentence Correction.
That vs. which? Restrictive vs. Non-restrictive
A restrictive modifier limits the conceivable scope of a general noun to a relevant subset. For example, consider the difference between the following two sentences:
1) I avoid dogs that appear too excited.
2) I avoid dogs, which appear too excited.
The first sentence conveys that I have a problem with some particular category of dogs — those dogs that seem too excited. Conceivably, even someone generally fond of dogs might say this about some narrow subset of dogs. The second sentence is a much more scathing statement: it suggests that I avoid all dogs, and the modifier acts as a judgment, almost a blanket condemnation, that I make about absolutely all dogs: they appear too excited. The first, containing the word “that”, is a restrictive clause, which narrows the scope from all dogs to a more specific subset. The second, containing the word “which”, is a non-restrictive clause, which simply adds a judgment to the whole category of dogs. In a choice between “that” and “which”, “that” must be used for the restrictive clause, and “which” for the non-restrictive clause. (By the way, lest any reader fret — outside of the foregoing hypothetical example, I really love all dogs!)
How do I pick?
How can you tell whether a clause should be restrictive or not? Well, one easy trick is to state the sentence without the clause. A restrictive clause provides vital information, so when it is dropped, the meaning of the sentence changes. A non-restrictive clause may provide helpful or interesting information, but when it is dropped, there is absolutely no ambiguity about the identity of the noun, and the sentence retains the same meaning. In the following sentences, see whether you can tell whether the underlined clause should be restrictive or non-restrictive, and thus, whether the word “that” or “which” should be used.
1) Mortimer can’t drive cars (that/which) have a standard transmission.
2) My favorite bridge is the Brooklyn Bridge (that/which) spans the East River in New York City.
3) Dr. Martin Luther King openly questioned laws (that/which) instituted injustice.
In sentence #1, it is certainly not true that all cars have a standard transmission! The vast majority of modern cars (depending on the country) have automatic transmissions, which means that the only logical choice is the restrictive clause. Dropping the clause seems to suggest that Mortimer can’t drive at all, which has a different meaning than a statement about his ability to drive a car with a standard transmission. In #4, there is only one Brooklyn Bridge in the whole world, so dropping the clause leaves absolutely no doubt about its identity: we need the non-restrictive clause. In #3, Dr. King was not an anarchist who questioned absolutely all laws. To the contrary, he was a highly principled individual who raised profound moral questions about a particular subset of laws — racially unjust ones. Therefore, the restrictive clause is needed. The corrected sentences are:
1) Mortimer can’t drive cars that have a standard transmission.
2) My favorite bridge is the Brooklyn Bridge, which spans the East River in New York City
3) Dr. Martin Luther King openly questioned laws that instituted injustice.
What about commas?
You may have noticed another subtle difference. A non-restrictive clause needs to be set off from the noun it modifies by commas. Commas should not set off a restrictive clause from the noun it modifies. When there’s a “that”/”which” distinction, this comma rule can tell us whether the clause is restrictive or not. When the same relative pronoun is used in both cases, sometimes our only clue is the punctuation. Consider these two sentences:
1) Bartholomew doesn’t like people who talk too much.
2) Bartholomew doesn’t like people, who talk too much.
Just one comma, but a world of difference! The first, without commas, is a restrictive clause that narrows the topic down from all human beings to a subset: just those folks who (according to Bartholomew) talk too much. We would need to know a little more about our hypothetical friend Bartholomew to know how reasonable his judgment is, but at least in some interpretations, we could easily imagine that this is a sentiment that many people hold. In the second sentence, the clause is separated by a comma, which tells us that it’s non-restrictive. In that sentence, our friend Bartholomew seems to have some major issues: he doesn’t like anyone. Here, the modifier implies that he doesn’t like people because, according to him, all of them talk too much. It would be exceedingly hard to imagine that such a person has a sane and happy life! This exemplifies the profound difference commas can make in the meaning of a sentence.
If you understand this distinction between restrictive vs. non-restrictive clauses, you will master one of the most confusing areas of GMAT Sentence Correction — and you will get “that” vs. “which” right every time!