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souvik101990
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20 Jan 2015, 05:09
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GMAT Sentence Correction: How To Find the Core Sentence
From the Manhattan GMAT Blog
Recently, I was discussing sentence structure with one of my classes and we practiced a crucial but difficult GMAT skill: how to strip an SC sentence to its core components. Multiple OG problems can be solved just by eliminating faulty sentence cores—and the real GMAT is testing this skill today more than we see in the published materials.
So I’m going to write a series of articles on just this topic; welcome to part 1 (and props to my Wednesday evening GMAT Fall AA class for inspiring this series!).
Try out this GMATPrep® problem from the free exams. (Note: in the solution, I’m going to discuss aspects of our SC Process; if you haven’t learned it already, go read about it right now, then come back and try this problem.)
* “With surface temperatures estimated at minus 230 degrees Fahrenheit, Jupiter’s moon Europa has long been considered far too cold to support life, and with 60 square miles of water thought to be frozen from top to bottom.
“(A) Europa has long been considered far too cold to support life, and with
“(B) Europa has long been considered far too cold to support life, its
“(C) Europa has long been considered as far too cold to support life and has
“(D) Europa, long considered as far too cold to support life, and its
“(E) Europa, long considered to be far too cold to support life, and to have”
The First Glance does help on this one, but only if you have studied sentence structure explicitly. Before I did so, I used to think: “Oh, they started with Europa because they added a comma in some answers, but that doesn’t really tell me anything.”
But I’ve learned better! What is that comma replacing? Check it out: the first three answers all have a verb following Europa. The final two don’t; that is, the verb disappears. That immediately makes me suspect sentence structure, because a sentence does have to have a verb. If you remove the main verb from one location, you have to put one in someplace else. I’ll be watching out for that when I read the sentence.
And now it’s time to do just that. As I read the sentence, I strip it down to what we call the “sentence core” in my mind. It took me a long time to develop this skill. I’ll show you the result, first, and then I’ll tell you how I learned to do it.
The “sentence core” refers to the stuff that has to be there in order to have a complete sentence. Everything else is “extra”: it may be important later, but right now, I’m ignoring it.
I greyed out the portions that are not part of the core. How does the sentence look to you?
Notice something weird: I didn’t just strip it down to a completely correct sentence. There’s something wrong with the core. In other words, the goal is not to create a correct sentence; rather, you’re using certain rules to strip to the core even when that core is incorrect.
Using this skill requires you to develop two abilities: the ability to tell what is core vs. extra and the ability to keep things that are wrong, despite the fact that they’ll make your core sound funny. The core of the sentence above is:
Europa has long been considered too cold to support life, and.
Clearly, that’s not a good sentence! So why did I strip out what I stripped out, and yet leave that “comma and” in there? Here was my thought process:
* Why isn’t estimated a verb?
Estimated is a past participle and can be part of a verb form, but you can’t say “Temperatures estimated at minus 230 degrees Fahrenheit.” You’d have to say “Temperatures are estimated at…” (Note: you could say “She estimated her commute to be 45 minutes from door to door.” In other words, estimated by itself can be the main verb of a sentence. In my example, though, the subject is actually doing the estimating. In the GMATPrep problem above, the temperatures can’t estimate anything!)
** Why is it that I expected another complete sentence to follow the “comma and”?
The word and is a parallelism marker; it signals that two parts of the sentence need to be made parallel. When you have one complete sentence, and you follow that with “comma and,” you need to set up another complete sentence to be parallel to that first complete sentence.
For example:
She studied all day, and she went to dinner with friends that night.
The portion before the and is a complete sentence, as is the portion after the and.
(Note: the word and can connect other things besides two complete sentences. It can connect other segments of a sentence as well, such as: She likes to eat pizza, pasta, and steak. In this case, although there is a “comma and” in the sentence, the part before the comma is not a complete sentence by itself. Rather, it is the start of a list.)
Okay, so my core is:
Europa has long been considered too cold to support life, and.
And that’s incorrect. Eliminate answer (A). Either that and needs to go away or, if it stays, I need to have a second complete sentence. Since you know the sentence core is at issue here, check the cores using the other answer choices:
Here are the cores written out:
“(B) Europa has long been considered too cold to support life.
“(C) Europa has long been considered as too cold to support life and has 60 square miles of water.
“(D) Europa and its 60 square miles of water.
“(E) Europa.”
(On the real test, you wouldn’t have time to write that out, but you may want to in practice in order to build expertise with this technique.)
Answers (D) and (E) don’t even have main verbs! Eliminate both. Answers (B) and (C) both contain complete sentences, but there’s something else wrong with one of them. Did you spot it?
The correct idiom is consider X Y: I consider her intelligent. There are some rare circumstances in which you can use consider as, but on the GMAT, go with consider X Y. Answers (C), (D), and (E) all use incorrect forms of the idiom.
Answer (C) also loses some meaning. The second piece of information, about the water, is meant to emphasize the fact that the moon is very cold. When you separate the two pieces of information with an and, however, they appear to be unrelated (except that they’re both facts about Europa): the moon is too cold to support life and, by the way, it also has a lot of frozen water. Still, that’s something of a judgment call; the idiom is definitive.
The correct answer is (B).
Key Takeaways: Strip the sentence to the Core
(1) Generally, this is a process of elimination: you’re removing the things that cannot be part of the core sentence. With rare exceptions, prepositional phrases typically aren’t part of the core. I left the prepositional phrase of water in answers (C) and (D) because 60 square miles by itself doesn’t make any sense. In any case, prepositional phrases never contain the subject of the sentence.
(2) Other non-core-sentence clues: phrases or clauses set off by two commas, relative pronouns such as which and who, comma + -ed or comma + ing modifiers, -ed or –ing words that cannot function as the main verb (try them in a simple sentence with the same subject from the SC problem, as I did with temperatures estimated…)
(3) A complete sentence on the GMAT must have a subject and a working verb, at a minimum. You may have multiple subjects or working verbs. You could also have two complete sentences connected by a comma and conjunction (such as comma and) or a semi-colon. We’ll talk about some additional complete sentence structures next time.
* GMATPrep® questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.
souvik101990
Expert
Alum
Joined: 19 Mar 2012
Last visit: 11 Nov 2025
Posts: 4,313
Given Kudos: 2,326
Location: United States (WA)
Concentration: Leadership, General Management
Schools: Ross '20 (M)
GMAT 1: 760 Q50 V42
GMAT 2: 740 Q49 V42 (Online)
GMAT 3: 760 Q50 V42 (Online)
GPA: 3.8
WE:Marketing (Non-Profit and Government)
Products:
Expert reply
20 Jan 2015, 05:13
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Welcome to the second installment of our Core Sentence series; if you haven’t yet read Part 1, do so now before continuing with this segment. How has your practice been going? It’s hard to develop the ability to “grey out” parts of the sentence in your mind. Did you find that you were able to do so without writing anything down? Or did you find that the technique solidified better when you did write out the core sentence?
Most people do have to start, in practice, by writing out the core. The goal is to be able to do everything (or almost everything) in your head by the time the real test rolls around.
Try out this GMATPrep® problem from the free exams; give yourself about 1 minute 20 seconds. (You can always choose to spend a little longer, since that time is an average, not a limit; more than about 20-30 seconds longer, though, typically just indicates that you’ve gotten stuck. At that point, guess from among the remaining answers and move on.)
* “Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organ pipe and spectacle lenses.
“(A) Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he
“(B) Galileo had not invented the telescope, but when he heard, in 1609, of such an optical instrument having been made,
“(C) Galileo, even though he had not invented the telescope, on hearing, in 1609, that such an optical instrument had been made, he
“(D) Even though Galileo did not invent the telescope, on hearing, in 1609, that such an optical instrument had been made,
“(E) Even though Galileo did not invent the telescope, but when he heard, in 1609, of such an optical instrument being made, he”
The First Glance shows a possible sentence structure issue: The first two start with a noun and verb, while the third tosses in a comma after that subject. I’m definitely going to need to check for that verb later!
The final two start with even though, which signals a clause, but a dependent one. That means I’ll have to make sure there’s an independent clause (complete sentence) somewhere later on.
Time to read the original sentence. It’s decently complex. What’s the core sentence?
Here’s the core:
Galileo did not invent the telescope, but he built his own device.
This actually consists of two complete sentences connected by a “comma and” conjunction. There’s nothing wrong with the core on this one. Now, you have a choice. You can check the modifiers in the original sentence (and, indeed, if you did spot any problems, you’d want to go deal with those right away). If not, though, then start with those potential structure issues spotted during the first glance.
Strip out the core for the other four answers:
“(B) Galileo had not invented the telescope, but quickly built his own device.
“(C) Galileo he quickly built his own device.
“(D) Even though Galileo did not invent the telescope, quickly built his own device.
“(E) Even though Galileo did not invent the telescope, but he quickly built his own device.”
Excellent! Now we have something to work with! Answer (C) doubles the subject; we don’t need to say both Galileo and he.
Answers (D) and (E) both start with even though, creating a dependent clause. Answer (D) doesn’t have an independent clause later because the part after the comma is missing the subject he.
Note: answer (B) might appear to have the same problem as (D), but the structures are not the same. Answer (B) begins with an independent clause. In this case, it’s okay to say the subject only once at the beginning and then attach two different verbs (had not invented and built) to that subject. (You may still think this one sounds funny. More on this below.)
Answer (E) does have an independent clause later, but there’s a meaning problem. The word but already indicates a contrast. Using both even though and but to connect the two parts of the sentence is redundant.
Okay, (C), (D) and (E) have all been eliminated. Now, compare (A) and (B) directly.
“(A) Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he
“(B) Galileo had not invented the telescope, but when he heard, in 1609, of such an optical instrument having been made,”
There are a couple of different ways to tackle this, but I’m going to stick to the sentence structure route, since that’s our theme today. Answer (B) does have one more clause in it, though it’s a dependent clause:
“Galileo had not invented the telescope, but when he heard of such an optical instrument having been made, quickly built his own device.”
Now, we do have a problem with the structure! If that intervening dependent clause weren’t there at all, then the core could have been okay: Subject verb, but verb. Technically, you wouldn’t want a comma there, but that’s really the only small issue.
When, however, you introduce a dependent clause in the middle, you can’t carry that original subject, Galileo, all the way over to the second verb at the end. Instead, as with answer (D), you need a complete sentence after the dependent clause, something like:
Galileo did not invent the telescope, but when he heard that one had been made, HE quickly built his own device.
Answer (B) is also incorrect.
The correct answer is (A).
You’re halfway through! Join me next time, when we’ll take a look at another type of complex sentence structure used commonly on the GMAT.
(1) Generally, this is a process of elimination: you’re removing the things that cannot be part of the core sentence. With rare exceptions, prepositional phrases typically aren’t part of the core. I left the prepositional phrase of water in answers (C) and (D) because 60 square miles by itself doesn’t make any sense. In any case, prepositional phrases never contain the subject of the sentence.
(2) Other non-core-sentence clues: phrases or clauses set off by two commas, relative pronouns such as which and who, comma + -ed or comma + ing modifiers, -ed or –ing words that cannot function as the main verb (try them in a simple sentence with the same subject from the SC problem, as I did with temperatures estimated…)
(3) A complete sentence on the GMAT must have a subject and a working verb, at a minimum. You may have multiple subjects or working verbs. You could also have two complete sentences connected by a comma and conjunction (such as comma and) or a semi-colon. We’ll talk about some additional complete sentence structures next time.
* GMATPrep® questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.
Most people do have to start, in practice, by writing out the core. The goal is to be able to do everything (or almost everything) in your head by the time the real test rolls around.
Try out this GMATPrep® problem from the free exams; give yourself about 1 minute 20 seconds. (You can always choose to spend a little longer, since that time is an average, not a limit; more than about 20-30 seconds longer, though, typically just indicates that you’ve gotten stuck. At that point, guess from among the remaining answers and move on.)
* “Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organ pipe and spectacle lenses.
“(A) Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he
“(B) Galileo had not invented the telescope, but when he heard, in 1609, of such an optical instrument having been made,
“(C) Galileo, even though he had not invented the telescope, on hearing, in 1609, that such an optical instrument had been made, he
“(D) Even though Galileo did not invent the telescope, on hearing, in 1609, that such an optical instrument had been made,
“(E) Even though Galileo did not invent the telescope, but when he heard, in 1609, of such an optical instrument being made, he”
The First Glance shows a possible sentence structure issue: The first two start with a noun and verb, while the third tosses in a comma after that subject. I’m definitely going to need to check for that verb later!
The final two start with even though, which signals a clause, but a dependent one. That means I’ll have to make sure there’s an independent clause (complete sentence) somewhere later on.
Time to read the original sentence. It’s decently complex. What’s the core sentence?
Here’s the core:
Galileo did not invent the telescope, but he built his own device.
This actually consists of two complete sentences connected by a “comma and” conjunction. There’s nothing wrong with the core on this one. Now, you have a choice. You can check the modifiers in the original sentence (and, indeed, if you did spot any problems, you’d want to go deal with those right away). If not, though, then start with those potential structure issues spotted during the first glance.
Strip out the core for the other four answers:
“(B) Galileo had not invented the telescope, but quickly built his own device.
“(C) Galileo he quickly built his own device.
“(D) Even though Galileo did not invent the telescope, quickly built his own device.
“(E) Even though Galileo did not invent the telescope, but he quickly built his own device.”
Excellent! Now we have something to work with! Answer (C) doubles the subject; we don’t need to say both Galileo and he.
Answers (D) and (E) both start with even though, creating a dependent clause. Answer (D) doesn’t have an independent clause later because the part after the comma is missing the subject he.
Note: answer (B) might appear to have the same problem as (D), but the structures are not the same. Answer (B) begins with an independent clause. In this case, it’s okay to say the subject only once at the beginning and then attach two different verbs (had not invented and built) to that subject. (You may still think this one sounds funny. More on this below.)
Answer (E) does have an independent clause later, but there’s a meaning problem. The word but already indicates a contrast. Using both even though and but to connect the two parts of the sentence is redundant.
Okay, (C), (D) and (E) have all been eliminated. Now, compare (A) and (B) directly.
“(A) Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he
“(B) Galileo had not invented the telescope, but when he heard, in 1609, of such an optical instrument having been made,”
There are a couple of different ways to tackle this, but I’m going to stick to the sentence structure route, since that’s our theme today. Answer (B) does have one more clause in it, though it’s a dependent clause:
“Galileo had not invented the telescope, but when he heard of such an optical instrument having been made, quickly built his own device.”
Now, we do have a problem with the structure! If that intervening dependent clause weren’t there at all, then the core could have been okay: Subject verb, but verb. Technically, you wouldn’t want a comma there, but that’s really the only small issue.
When, however, you introduce a dependent clause in the middle, you can’t carry that original subject, Galileo, all the way over to the second verb at the end. Instead, as with answer (D), you need a complete sentence after the dependent clause, something like:
Galileo did not invent the telescope, but when he heard that one had been made, HE quickly built his own device.
Answer (B) is also incorrect.
The correct answer is (A).
You’re halfway through! Join me next time, when we’ll take a look at another type of complex sentence structure used commonly on the GMAT.
Key Takeaways: Strip the sentence to the Core
(1) Generally, this is a process of elimination: you’re removing the things that cannot be part of the core sentence. With rare exceptions, prepositional phrases typically aren’t part of the core. I left the prepositional phrase of water in answers (C) and (D) because 60 square miles by itself doesn’t make any sense. In any case, prepositional phrases never contain the subject of the sentence.
(2) Other non-core-sentence clues: phrases or clauses set off by two commas, relative pronouns such as which and who, comma + -ed or comma + ing modifiers, -ed or –ing words that cannot function as the main verb (try them in a simple sentence with the same subject from the SC problem, as I did with temperatures estimated…)
(3) A complete sentence on the GMAT must have a subject and a working verb, at a minimum. You may have multiple subjects or working verbs. You could also have two complete sentences connected by a comma and conjunction (such as comma and) or a semi-colon. We’ll talk about some additional complete sentence structures next time.
* GMATPrep® questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.
General Discussion
07 Feb 2017, 15:58
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Hello there,
Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organ pipe and spectacle lenses
I've a question regarding your explanation, what does "on hearing" work as in the sentence because they sound like random set of words ( as far as I know its neither a phrase nor a clause). would appreciate answer
Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organ pipe and spectacle lenses
I've a question regarding your explanation, what does "on hearing" work as in the sentence because they sound like random set of words ( as far as I know its neither a phrase nor a clause). would appreciate answer
