No guide sufficiently teaches you when to drop certain terms in parallelism.

Question

I've looked everywhere, and no guide really explains it well. The only OK one is in MGMAT SC book, which says that you need to repeat the front terms if there is a closed parallel marker. Example: not in x but also in y. --> IN MUST be repeated. In open markers, it's not clear. Consider the following incorrect sentence: The discovery that Earth’s inner core rotates independently of and more quickly than Earth’s outer layers is responsible for advancing studies of how heat from the inner core flows through the outer planet, and the formation and periodic reversal in direction of Earth’s magnetic field This is wrong because there is no second OF: studies OF how heat... and OF the formation.. would be correct. How the heck am I supposed to know what to drop and what to not put? MGMAT SC says to replace an element in front of the start to see if it makes sense. The discovery that Earth’s inner core rotates independently of and more quickly than Earth’s outer layers is responsible for advancing studies of the formation and periodic reversal in direction of Earth’s magnetic field. This makes sense, so why does OF need to be repeated again? Why can't the OF be distributed to both? The most frustrating part is that no guide really tells you exactly what should be done. Everybody just says "needs OF because of parallelism". But in many cases, the front part can be dropped and still be parallel. So when exactly can you drop and when can you not? I thought this one was OK because the sentence completely makes sense if I put the second element in front of the first OF, so OF can be distributed.

Answer 1

Parallelism means that like things are to be treated in like manner. The author speaks of "studies" dealing with two like things: how heat flows etc., and the formation and reversal etc. Therefore the sentence must refer to studies OF one and studies OF the other. Including the second "of" allows the author to drop that second "studies," which becomes redundant since it's clearly meant to apply to both prepositional phrases ("of how heat..." and "of the formation...") Here's maybe an even clearer way to look at it. Suppose the second "of" were to be omitted. Here's what the sense of the sentence would become:

The discovery [etc.] is responsible for:

advancing studies of how heat etc...

AND

the formation and reversal etc.

Do you see? Without the second "of," the parallel elements become "advancing" and "formation." Which makes no sense of course, because how can some "discovery" be "responsible for" facets of earth's magnetic field? On the other hand, with the second "of" included, everything makes sense: The discovery is now responsible for one thing, namely. advancing two kinds of studies.

To tell you the truth, even the corrected sentence isn't the greatest, because the two studies' topics should be in parallel form as well. The best possible, most elegant version would go something like "...responsible for advancing studies of the flow of heat from the inner core through the outer planet, and of the formation and periodic reversal in direction of Earth’s magnetic field." I have underlined the parallel elements, and you should note that the meaning remains intact. However, the parallelism of "studies of X....and of Y" is the more important issue, in order to avoid the huge error I describe above. Using "how heat flows" with "the formation" isn't wrong, just clunky. But omitting the second "of" would be wrong.

I mention that last hypothetical just to help you better understand the music of a strong, elegant, correct sentence. Keep practicing parallelism examples and analyzing how like things are treated in like manner, over and over. Keep making mistakes, too. Eventually you'll get the hang of it.