Comparing or contrasting two things or ideas is a common function of Sentence Correction questions on the GMAT. GMAT Comparison and contrast errors fall into two main categories:
(1) using incorrect and unidiomatic wordings to express the comparison/contrast
(2) creating an illogical comparing/contrasting between the wrong things.
GMAT Sentence Correction: Comparing or contrasting two things or ideas
We’ll begin with two examples of idiomatic failure in comparisons and contrasts and then transition to two examples of logical failure. Here’s an interesting Official Guide question:
GMAT Comparison and Contrast Question
Like ancient Egyptian architectural material that were recycled in the construction of ancient Greek Alexandria, so ancient Greek materials from the construction of that city were reused in subsequent centuries by Roman, Muslim, and modern builders.
(A) Like ancient Egyptian architectural material that were recycled in the construction of
(B) Like recycling ancient Egyptian architectural materials to construct
(C) Just as ancient Egyptian architectural materials were recycled in the construction of
(D) Just as they recycled ancient Egyptian architectural materials in constructing
(E) Just like ancient Egyptian architectural materials that were recycled in constructing
A question as ancient as these architectural materials: should we use “like” or “as” for this comparison? Here’s the rule: when the element being compared to or contrasted against has a verb attached to it, use “as” or “just as,” followed by “so” on the other side of the comparison/contrast.
This sentence is mainly about the ancient Greek architectural materials, which are being compared to ancient Egyptian architectural materials. Since the ancient Egyptian architectural materials are attached to the verbal phrase “were recycled,” the correct comparative idiom is “(just) as / so (also),” not “like.”
Only answer choices C and D use the correct idiom, but choice D awkwardly mentions a “they” recycling the ancient Egyptian materials. First of all, who are “they”? And second of all, there’s no “they” on the Greek materials side of this comparison, so introducing a “they” breaks parallelism. C is the correct answer choice.
Note the parallelism of the resulting construction:
Just as ancient Egyptian architectural materials were recycled . . .
so ancient Greek materials . . . were reused . . .
This was a great way to learn the rule governing the use of the two idioms (just) as/so (also) and like. But I should point out that since the second part of the comparison, which isn’t underlined, begins with “so” (so ancient Greek materials constructed), we know right away that the sentence must begin with “as” or “just as.” “Like _____, so _____” is unidiomatic and incorrect.
Again we see that using the elements of the sentence outside the underlined portion can help us make quick decisions. The context surrounding the underlined portion is critical for determining which answer choices might make sense.
GMAT Comparison and Contrast Question
Let’s take a look at another comparative question:
As with ants, the elaborate social structure of termites includes a few individuals reproducing and the rest serve the colony by tending juveniles, gathering food, building the nest, or battling intruders.
(A) As with ants, the elaborate social structure of termites includes a few individuals reproducing
(B) As do ants, termites have an elaborate social structure, which includes a few individuals to reproduce
(C) Just as with ants, termite social structure is elaborate, including a few individuals for reproducing
(D) Like ants, termites have an elaborate social structure in which a few individuals reproduce
(E) Like that of ants, the termite social structure is elaborate, including a few individuals that reproduce
This time both sides of our comparison are underlined. The introduction “as with ants” is somewhat vague and unclear. Also, there is no verb attached to these ants, so “as” is incorrect anyway. Since both sides of the comparison are underlined, we can’t tell immediately how this sentence needs to begin. We could probably imagine some ways to write this sentence that begin with “like” and some other ways that begin with “just as.”
Again, attentiveness to the elements of the sentence outside the underline is the quickest way forward. Immediately after the underline is the phrase “and the rest serve . . .” Since the sentence continues this way, we should try to find an answer choice that ends with “a few individuals reproduce.” We want the form of the verb “reproduce” to match the form of the verb “serve.” Let’s check the form of “reproduce” in the answer choices:
(A) individuals reproducing
(B) individuals to reproduce
(C) individuals for reproducing
(D) individuals reproduce
(E) individuals that reproduce\
D is correct!
a few individuals reproduce
the rest serve
This is the parallelism we wanted. And of course, the comparison at the beginning of choice D is correctly constructed.
Choice E is interesting because it begins with the promising comparison “Like that of ants, the termite social structure . . .” Unfortunately, the way this answer choice continues doesn’t jive with the rest of the sentence. But it brings up an interesting point.
In this sentence, we could have compared termites to ants or termite social structure to ant social structure. This second option is what choice E was starting to do. Comparisons or contrasts between two possessions or traits need a phrase like “that of” or “those of.” Forgetting to use this phrase can lead to an illogical comparison.
We don’t want to compare termites themselves to ant social structures, or termite social structures to ants themselves. Every comparison/contrast must be bug to bug or social structure to social structure.
GMAT Comparison and Contrast Question
Here’s another problem to follow up this point:
The eyes of the elephant seal adapt to darkness more quickly than any other animal yet tested, thus allowing it to hunt efficiently under the gloomy conditions at its feeding depth of between 300 and 700 meters.
(A) The eyes of the elephant seal adapt to darkness more quickly than any other animal yet tested, thus allowing it
(B) The eyes of the elephant seal adapt to darkness more quickly than does any other animal yet tested, allowing them
(C) The eyes of the elephant seal adapt to darkness more quickly than do those of any other animal yet tested, allowing it
(D) Because they adapt to darkness more quickly than any other animal yet tested, the eyes of the elephant seal allow it
(E) Because the eyes of the elephant seal adapt to darkness more quickly than do those of any other animal yet tested, it allows them
This is not a “like” or “just as” comparison. Instead, it’s about the degree or extent to which something is true.
Here are some simple example forms:
X is as _____ as Y is.
X is more _____ than Y is.
X is less ____ than Y is.
Let’s diagnose the given version of the sentence. Does it establish a logical comparison? One that is animal to animal or eyes to eyes? No, it doesn’t. It is eyes to animal, which doesn’t make sense. There are potentially a few ways for this to go, but the “minimally invasive” correction is to simply insert the phrase “do those of” before “any other animal yet tested.”
A quick scan of the answer choices shows us that choice C does this very thing. C is the correct answer choice.
The presence of the verb “do” before “those of” might feel stuffy and unnecessary. But this is mainly because the word order (the official term is syntax) is not what we’re used to in conversational English. We can reassure ourselves about the appropriateness of this wording by flipping the syntax:
The eyes of the elephant seal adapt to darkness more quickly than other animals’ eyes do.
This sounds natural. But what if we include all the details and use “those of,” as the original sentence did?
The eyes of the elephant seal adapt to darkness more quickly than those of any other animal yet tested do.
Since “those” is filling in for the subject “eyes,” the associated verb “do” is now awkwardly far away. We can see how it’s actually clearer and better to say “than do those of,” as in answer choice C.
GMAT Comparison and Contrast Question
Let’s look at a final question, this time a contrast:
Unlike the virginal, whose single set of strings runs parallel to the front edge of the instrument, the harpsichord’s several sets of strings are placed at right angles to its front edge.
(A) whose single set of strings runs parallel to the front edge of the instrument, the harpsichord’s several sets of strings are
(B) with a single set of strings running parallel to the front edge of the instrument, the several sets of strings of the harpsichord are
(C) which has a single set of strings that runs parallel to the front edge of the instrument, in the case of the harpsichord, several sets of strings are
(D) which has a single set of strings that run parallel to the front edge of the instrument, the harpsichord has several sets of strings
(E) in which a single set of strings run parallel to the front edge of the instrument, the harpsichord’s several sets of strings are
This question can be dizzying, but if you’re practiced at comparison/contrast questions, you can answer it quickly. Key observation: “Unlike the virginal” isn’t underlined! We are contrasting against the virginal itself, not against the virginal’s strings or sets of strings. We need the sentence to go like this:
Unlike the virginal . . . the harpsichord
As soon as the sentence finishes giving the parenthetical information about the virginal’s strings, it needs to refer directly to the harpsichord, not to the harpsichord’s strings or sets of strings. Look to the relevant position in the answer choices, and you’ll see that only choice D refers directly to the harpsichord!
(A) the harpsichord’s several sets of strings
(B) the several sets of strings of the harpsichord
(C) in the case of the harpsichord, several sets of strings
(D) the harpsichord
(E) the harpsichord’s several sets of strings
D is the correct answer.
Many incorrect GMAT comparison and contrast answer choices use the “possessive trap” seen here in answer choices C and E. By using the possessive phrase “the harpsichord’s,” these choices try to look like they are referring directly to the instrument itself. But the possessive kicks back the reference to the several sets of strings, making the comparison illogical.
On GMAT comparison and contrast questions, look out for those possessives.
To learn more about another common error, check out our next article on “Common Sentence Correction Errors: Animals and Agreement.“
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Contributor: Elijah Mize (Apex GMAT Instructor)