The Knewton Blog

In our GMAT Case Study series, we’ll take a close look at the key concepts behind GMAT practice questions. This week: idiom errors.

Even the most diligent students occasionally have nightmares about GMAT sentence correction grammar. SC can be particularly frustrating if you are not a native English speaker and have trouble just understanding what the sentence is saying. Luckily, there are plenty of strategies to help test-takers — both native and non-native speakers — succeed! Before we get into too many details, let’s try an example:

In the last few decades, physicists have identified the existence of different “flavors” of subatomic particles called quarks, most of them as small or smaller than the electron, which display a property known as color charge.

(A) most of them as small or smaller than the electron, which display

(B) most of them as small or smaller than the electron and displaying

(C) mostly as small or smaller than the electron, displaying

(D) mostly at least as small as the electron, which display

(E) most of them at least as small as the electron, displaying

Give it a shot, then read on for the explanation and more SC strategy tips.

Not sure what “quarks” and/or “electrons” are? Don’t worry! Lucky for you, the content of this sentence is pretty much irrelevant. As long as you can identify the parts of speech, you can get a handle on what the sentence is testing.

Try to approach sentence correction the same way as math. Ignore the vocabulary and writing style and instead think of the sentence as an equation. Your job for SC questions is to balance the equation by making sure all the necessary elements are in place.

Okay, back to the sample question. If English is not your first language, then it may be difficult for you to spot the idiom error in the sentence. However, we can start with a more basic grammar error, which you have already likely encountered in a grammar book or GMAT question.

Look at the word “which.” The phrase, which display does not make sense here because adjective clauses that start with “which” MUST refer to the object they follow. Here, which display would refer to electron. “Electron, which display” does not make sense grammatically — it would have to be “displays.” Furthermore, it is not the electron that is displaying a property known as color charge — it is the quarks that are doing this.

Again, you don’t need to know what “quarks” and “electrons” are to answer this question — you just need to know that they are nouns. To balance the grammar “equation” here, we need an expression that either uses the word “which” logically, or does not use it at all. Therefore we can immediately eliminate answer choices A and D.

Let’s look at another part of the sentence: the word “most.” Notice how two answer choices use the word “mostly”? If you remember your parts of speech, you know that we add “-ly” to adjectives to turn them into adverbs. Here “most” is describing “quarks,” a noun. Therefore we should use an adjective, not an adverb. We can eliminate answer choice C.

Now it is down to just B and E. If you are unaware of the idiom error (“as small or smaller than” is incorrect. You cannot say “as X…than”) then try to judge the two options by sound. Which one is less awkward? Choice E, with its balanced use of commas and adjectives, reads much more naturally than B.

And it just so happens that choice E is correct. What’s the moral of the story? Break down an SC question into components and begin eliminating wrong answer choices based on the errors you know. You will improve your chances of finding the right answer and save time trying to decipher meaning.