Sentence Correction: Logical Approach to Comparison and Parallelism

Written by Kelly Granson. Posted in GMAT Study Guide

parallelism and comparison (theory)The basics of parallelism are not hard to grasp: when you list or compare items they should be parallel, that is, have the same grammatical form. But if parallelism is that simple, then why is GMAT so keen on testing it? First, flaws in parallelism are often difficult to recognize. Second, simple grammatical similarity is sometimes insufficient (even occasionally unnecessary)—elements of a parallel structure must be logically similar to each other. These are the challenges this discussion will address.

How do you recognize a flaw in parallelism? Actually, any sentence that lists several things can have such a flaw. Here is an example.

Brian's activities at college included editing a newspaper, playing soccer, and work as a chemistry tutor.

Here is the short list of Brian's activities: editing, playing, and work. The last item on the list stands out because it is a noun, whereas the first two are gerunds. Gerunds and nouns cannot be on the same list. Stick to one grammatical form:

Brian's activities at college included editing a newspaper, playing soccer, and working as a chemistry tutor.

Things get a bit trickier, however, when you consider logic. Before converting all the items in a series into a single grammatical form, see if they are logically parallel. If they are, you may not have to change their grammar. Look at the following sentence, for example.

Although selected without any strict criteria and originating from diverse backgrounds, the survey participants gave similar responses.

I have seen many students misled by the lack of strict grammatical parallelism between such words as originating and selected. When faced with the need to correct a sentence of this kind, they tend to gravitate toward answer choices that make the structure parallel in terms of grammar: originated and selected or originating and being selected. These choices, however, do not make much sense; the participants originated themselves (not they were originated), therefore we need a present participle here, whereas selected should remain a past participle, because participants were selected. Originating and selected in this case are logically parallel modifiers of participants, so the sentence is correct as it is.

Here is another classic example of a sentence lacking proper parallel structure. In this case, the grammar is obviously correct, so what's wrong?

At college, Brian worked not only as a newspaper editor but also tutored chemistry.

Since worked and tutored are both verbs and in the same form, they appear to be parallel, so it may be hard to see what's wrong with this sentence. There is something wrong, however: the position of the verbs. Worked comes before not only, while tutored comes after but also. Worked and tutored, therefore, are not necessarily required to be parallel. Whatever stands directly after not only should be parallel to what comes after but also. There are at least two ways to correct this sentence: ...Brian worked not only as a newspaper editor but also as a chemistry tutor or ...Brian not only worked as a newspaper editor but also worked as a chemistry tutor. Note that the same principle applies to constructions such as either...or... and neither...nor....

Now let's look at comparisons, another type of structure where parallelism is a must.

Brian always found editing a newspaper much more enjoyable than chemistry.

It looks like we are trying to compare editing with chemistry in this sentence. This comparison, however, is both grammatically and logically incorrect. Newspaper editing is an activity, whereas chemistry is a subject area, so they are not comparable. The correct sentence might read Brian always found editing a newspaper much more enjoyable than teaching chemistry.

To qualify as grammatically and logically parallel, comparisons also have to be complete.

The rules of baseball are much harder to learn than basketball.

What are we comparing here? The rules of baseball and the rules of basketball, obviously. To avoid wordiness, you might feel tempted not to mention the rules of for a second time. It's not a good idea to leave it out, however, since without it the structure will not be grammatically parallel. Instead of leaving out the rules of, replace the rules of with those of (use that of for singular nouns), and you will get a nice sentence with a proper comparison: The rules of baseball are much harder to learn than those of basketball.

Another crucial feature of comparisons on GMAT is that they should be unambiguous. When you say I like oranges more than Mike, you probably mean that you like oranges more than Mike likes oranges. However, no matter how obvious this meaning might seem to be, the sentence still lends itself to the interpretation that you like oranges more than you like Mike. Since GMAT does not tolerate such ambiguity, a correct sentence should read, "I like oranges more than Mike DOES" if that is indeed what you mean.

Parallelism is extremely important, so much, in fact, that it usually trumps succinctness. If you have any experience with Sentence Correction problems, no doubt you are well aware of GMAT's emphasis on being concise. However, you should always go for a choice that exhibits proper parallelism, even if it isn't the most concise choice. Consider the following example.

The presenter has explained who is eligible for a scholarship, what factors are taken into consideration in the choice of suitable candidates, and the peculiarities of the application procedure.

In this sentence, the last item on the list should be and what the peculiarities of the application procedure are, even though it is longer and clumsier than the original phrase.

In summary, to handle parallelism problems with ease, keep in mind that there is one underlying principle at work: items on a list, parts of a comparison, and elements of certain other structures should have the same grammatical form and, even more importantly, logical similarity, neither of which can be sacrificed for the sake of succinctness.

The next post will include a GMAT sample questions so you can try to apply what you've learned here.

Good luck!


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