GMAT Sentence Correction: “That” versus “Which”

One of the common grammatical stumbling blocks for GMAT test-takers concerns the appropriate use of “that” and “which.” Although the difference between “that” and “which” will almost never be the make-or-break difference in a GMAT Sentence Correction question, understanding when each term is correct can help you quickly eliminate choices on test day.

The key difference between “that” and “which” is the following: “That” introduces information that is ESSENTIAL to understanding the meaning of a sentence, whereas “which” introduces NON-ESSENTIAL information. Let’s take a look at a couple sentences to see these differences in action.

Sentence 1: John likes bananas that are green.
Sentence 2: John likes bananas, which are high in potassium.

In sentence 1, the relative clause “that are green” introduces a fact that is NECESSARY to understand the writer’s intent. The writer is not telling us that John likes all bananas, but, rather, that he likes a subset of bananas: green ones. To understand the role of “that are green,” take it out of the sentence and look at how the meaning changes: “John likes bananas.” In the above sentence, the speaker’s meaning changes. It now sounds as if John is a fan of ALL bananas, not just green ones.

In sentence 2, the relative clause “which are high in potassium” provides information that adds to what the author states, but is NOT essential the sentence’s meaning. In this sentence, the modifier “which are high in potassium” does not restrict the types of bananas John likes, but, instead, provides extra, general information about these bananas. Whereas removing the “that” clause in sentence 1 changed the actual meaning of the sentence, removing the “which” clause here will not affect the sentence’s essential meaning: “John likes bananas.” Even though we’ve removed the relative clause here, the author’s intended meaning (that John likes ALL bananas) is preserved.

So next time you’re trying to decide whether to use “that” or “which,” ask yourself: Is this information necessary for the sentence to retain its meaning?