"Fred wrote to Congress to complain about this policy nearly four months before Silvia ____________"
What we want to say is --- Fred wrote to Congress, and Silvia also wrote to Congress, but Fred did what he did before Silvia did what she did. The question is --- how do we end that sentence eloquently in a way that means "did the same thing"? In other words, we want to repeat, in abbreviated form, the predicate. (The predicate is the verb and the entire phrase that follows it.) How do we repeat the predicate in abbreviated form? First, let's talk about the wrong answer.
Using the word "this" in a construction such as this would be wrong 100% of the time on the GMAT Sentence Correction. Why is that wrong? What is the correct thing to say?
Pronouns --- what they can and can't do
The word "this" is a pronoun, a demonstrative pronoun --- others include "that", "these", and "those." There are also personal pronouns ---- "I", "you", "he", "she", "they" (each of these also have possessive & objective forms --- "I", "my", "mine", "me", etc.) There are also indefinite pronouns, a large category including --- "someone", "everyone", "everyone", "no one", "anyone", then those five again with "body" or "thing" substituted for "one", the word "one" by itself, "each", "none", "all", "another", etc.
For the purposes of this blog, those are all just pronouns. The job of a pronoun is to substitute for a noun, to take the place of a noun. That's what pronouns do, and that's all they do.
When can we use a pronoun of some sort for repeating a predicate in abbreviated form? It would be legitimate to use a pronoun in this construction only if the first verb is a form of the verb "to do". Of all the tens of thousands of verbs in the English language that could be in the first predicate, only this one verb, the verb "to do", will allow us to use a pronoun in the second part.
1) Fred did the complicated procedure on page 137 of the manual before Silvia did it.
2) Fred will do his laundry before Silvia does hers.
3) Fred has done triple somersaults long before Silvia ever did one.
In all three of those, as it happens, the verb in the first part of the sentence was a form of the verb "to do". When repeating the predicate, we are using the exact same verb, "to do", and need only a pronoun of some kind to replace the noun, the direct object of the first verb. All well and good, but there are thousands of other verbs in the language for which this trick will not work.
For all other verbs ….
For all other verbs, we use a form of the verb "do" as a substitute for any other verb. When we are substituting the verb "to do" for another verb, we no longer can substitute a pronoun for the object. Instead, we are replacing the entire predicate, [verb] + [object]. For this, we use the magic word "so." The magic combination "do so" can substitute for any other possible predicate in the English language. This is by far the most concise way to accomplish this. Of course, one could use something wordier, such as "do the same thing" --- technically, that also would be grammatical correct, but such an awkward wordy monstrosity would never be acceptable on GMAT Sentence Correction. Examples:
4) Fred will rent a canoe before Silvia does so.
5) Fred insulted the hostess before Silvia also did so.
6) Fred climbed Mt. Kilimanjaro seven times before Silvia ever did so.
7) Fred has traveled to Bangkok every year since 1973, but this is the first time that Silvia has done so.
8) Fred wrote to Congress to complain about this policy nearly four months before Silvia did so.
This is grammatically correct, and exactly what the GMAT will expect on Sentence Correction, but exceedingly few people speak this way in casual conversation. This construction is so rare in colloquial English that it may sound unnatural to your ear. Retrain your ear, so that this construction sounds correct, because it is. It will help to elevate the level of your reading.
This post was written by Mike McGarry, GMAT expert at Magoosh, and originally posted here.