Concision is one of the goals of parallel structure. Consider the following monstrosity of a sentence.
1a) After I get my next paycheck, I am seriously thinking about buying a jet ski, I am seriously thinking about treating my friends to dinner, and I am seriously thinking about putting some money away in savings.
Obviously, that sentence is screaming for the simplification that parallel structure brings:
1b) After I get my next paycheck, I am seriously thinking about buying a jet ski, treating my friends to dinner, and putting some money away in savings. (Whew!)
Notice the words in 1a that were eliminated in 1b: the repeated phrase “I am seriously thinking about.” The repetition of that phrase is precisely what makes 1a sound hideously redundant. These words, the words that would be repeated in each piece of the parallel structure, are called the common words.
Cut the Repeated Common Words
One of the guiding principles of parallelism, one might even say the very point itself, is to streamline by eliminating repetitions of the common words. A common GMAT Sentence Correction wrong answer choice is of the form
[common words] A, B, and [common words]C
When A, B, and C are not single words, but rather long complicated phrases, it can be confusing to track the overall structure, and in its typical incorrect SC choices, the GMAT loves to “interrupt” the parallel structure by repeating some or all of the common words further down the list. This can be particularly tricky if the parallel structure begins before the underlined section and ends within the underline section. Here’s an example from the OG (one of the 20 new questions in the OG 13):
79) Ryunosuke Akutagawa‘s knowledge of the literatures of Europe, China and that of Japan were instrumental in his development as a writer, informing his literary style as much as the content of his fiction.
(A) that of Japan were instrumental in his development as a writer, informing his literary style as much as
(B) that of Japan was instrumental in his development as a writer, and it informed his literary style as well as
(C) Japan was instrumental in his development as a writer, informing both his literary style and
(D) Japan was instrumental in his development as a writer, as it informed his literary style as much as
(E) Japan were instrumental in his development as a writer, informing both his literary style in addition to
The parallel structure in this sentence is among the three cultural regions cited: Europe, China, and Japan. The common words are “knowledge of the literatures of”, and these words apply equal to all three terms. Notice that, in answer choices (A) and (B), the GMAT supplies us with the classic mistake structure described above. We have [common word] Europe, China, and [common word] Japan. What’s particularly confusing is that the words “that of” is a very typical GMAT SC turn of a phrase, often appearing in correct answer choices. Here, though, (A) & (B) have the classic mistake structure. I’ll discuss the rest of this question at the end of this post.
But Keep Some Common Words
This is the rule that adds nuance to the previous principle. When each of the three parallel elements is a single word, as is the case in the above sentence about Ryunosuke Akutagawa, then it’s appropriate to drop all repeated common words. Often, though, especially on the GMAT SC, the parallel elements are not single words but rather long complicated phrases or clauses. In that case, repeating a single common word, such as a preposition, can be crucial as a “signpost” for the parallel structure. One of the more inspiring examples of this comes from a talented young writer of another hemisphere:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.
In these famous words, the brilliant writer Thomas Jefferson alerts us to the parallel structure simple by introducing each new element with the word “that.” That single word univocally illuminates the parallel structure of the sentence. Another even loftier example:
In the midst of the candlesticks one like unto a son of man, clothed with a garment down to the foot, and girt about at the breasts with a golden girdle; and his head and his hair were white as white wool, white as snow; and his eyes were as a flame of fire; and his feet like unto burnished brass, as if it had been refined in a furnace; and his voice as the voice of many waters, and he had in his right hand seven stars: and out of his mouth proceeded a sharp two-edged sword: and his countenance was as the sun shineth in his strength.
In this richly poetic passage from the Book of Revelation (RSV, 1:13-16), the repeated word “and” acts as the signpost which guides us through the complex parallel structure. Admittedly, the word “and” is an unlikely choice as the single repeated word on GMAT SC, and divine eschatological revelation is an exceedingly unlikely topic, but I hope this gives you a sense of the diversity of possibilities for this grammatical structure.
Because of the balance of the previous two principles, every writer has a certain amount of discretion about how many of the common words are repeated, especially when there are only two term. Some parallel structures “bundle” the parallel items with a set of preceding signal words: for example, “both X and Y”, “neither J nor K”, “not only P but also Q” (right there are three of the GMAT’s favorite parallelism templates!)
The rule for this situation is a little more complex. Any common word that is not repeated must precede the first word of the signal words. Any word that appears after the first signal word must also appear after the second signal word. One outside is correct, and both inside is also correct, but an inside/outside combination is incorrect. For example, consider this faux sentence completion question. (I felt a somewhat less exemplary theme was in order after the foregoing examples!)
3) The senator bought a Valentine’s Day card for both his wife as well as for his mistress.
(A) for both his wife as well as for his mistress.
(B) for both his wife and also his mistress.
(C) both for his wife as well as for his mistress.
(D) for both his wife and for his mistress.
(E) both for his wife and for his mistress
The first thing we have to know: the correct structure recognized by the GMAT is “both A and B.” The GMAT views the structures “both A and also B” and “both A as well as B” as redundant and incorrect. Knowing this, we can immediately eliminate (A) & (B) & (C). Choice (B) would have been perfect without the word “also”, but as is, it’s wrong. Choice (D) falls foul of the bundling rule: the first “for” is before the word “both”, which should make it apply equally to both, but then a second “for” crops up in front of “his mistress.” One outside, one inside: the classic mistake format for this particular structure. Only (E) gets everything correct: it has the proper “both … and” structure, and the word “for” appears twice, once in front of each term. Another correct choice would have been “for both his wife and his mistress”, but that was not offered among these five answer choices.
An Addendum on the Ryunosuke Akutagawa question
I promised I would resolve that question from the OG. From parallelism, we have already eliminated (A) & (B), as discussed above. The subject of the sentence, “knowledge”, is singular, so the verb must be singular: “was”, not “were.” That eliminates (E). This leaves (C) and (D), which have many similarities. One difference is the ending. (C) ends simply with “and”, correctly completing the “both … and” structure. (D) avoids the word “both”, and instead ends with “as much as.” The phrase “as much as” is a comparative phrase —– “the teacher like me as much as she like you!” — but in this context, we are not performing a comparison. The two items in question are Akutagawa’s literary style and the content of his fiction. These both were informed by his vast knowledge of literature, but there’s nothing in the sentence that suggests a comparison is in order. (D) also has that awkward phrase “as it informed”, instead of the shorter and more direct “informing” in (C). For these reasons, (D) is incorrect, and (C) is by far the best answer choice.