Cases when it is necessary to supply a new word in GMAT Sentence Correction:
On GMAT Sentence Correction, your job is to correct grammatical mistakes, resolve ambiguities, and cut unnecessary verbiage — all without changing the meaning. Therefore, it would always be a bad idea to fill in more words that are not there, right? Not necessarily. In general, any answer choice that piles on a whole new phrase is not correct, but there are some instances when a new word, a word not appearing in the prompt is absolutely essential.
What Pronouns Can Do
In a good GMAT Sentence, every pronoun needs a clear antecedent. If we are talking about an individual object, that’s usually straightforward.
For years, the premier American hedge fund has invested in German Deutschmarks because they hold their value so well.
Here, the pronouns “they” and “their” refer unambiguously to “Deutschmarks”, the only plural noun in the sentence. This is an example of a correct sentence for GMAT Sentence Correction.
What Pronouns Can’t Do
What becomes tricky is if the antecedent is not a single word but involves a complex idea that takes a full clause to express. Here’s an example of an incorrect sentence:
While the American dollar has steadily declined over the last 60 years compared to the German Deutschmark, it has not caused the erosion ofthe American standard of living.
The major problem with this sentence is the word “it” — this word has no clear antecedent. The nouns (“American dollar”, “German Deutschmark”) are not the proper antecedents. In a way, thing to which the “it” wants to refer is the verb “declined.” That’s a problem, because a pronoun’s antecedent must be a noun. When you want the subject of the second half of a sentence to encapsulate the action of the verb, a pronoun simply can’t do that.
What You Can Do Instead
Here is an example of a GMAT-worthy corrected sentence on the same subject:
While the American dollar has steadily declined over the last 60 years compared to the German Deutschmark, this loss has not caused the erosion of the American standard of living.
Because we wanted the subject of the second half of the sentence to capture the action of the first half, we needed to come out with a new word, the word “loss” that describes, as a noun, exactly what happened in the first half. Actually, you don’t need to come up with this new word at all, because in Sentence Correction, the GMAT will simply provide the five answer choices for you. Nevertheless, you do need to be able to recognize this situation, and discern that an additional word is needed.