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GMAT Sentence Correction, SAT, ACT Advanced Grammar Rules

The SAT, the ACT, and the GMAT all have significant grammar sections. These can trip up students who aren’t prepared, and even those who are. Most students never really study English grammar, so they’re not quite sure what to make of these sections.

The good is that I am almost positive you can read English, considering you’re reading this blog post. If so, you already have what you need to do well on these sections. You just need to formalize your knowledge.

I’m not going to bother explaining the basic rules (apostrophes for possession, semicolons for independent clauses), because I figure you already know those. I want to explore some of the more difficult stuff.

Here goes.

Subject vs. object (e.g. who vs. whom)

When we use nouns and pronouns in English, they can either be subjects or objects. When they’re subjects, they do something. When they’re objects, they generally have something done to them.

Because English is a lazy language, we don’t change our nouns for subjects and objects, but we do change our pronouns.


“I throw the ball to him.” I is the subject, him is the object. I does something, him gets something to done to him (awkward to write that).

“He throws the ball to me.” He is the subject, me is the object. He does something, me gets something done to me.

“He throws the ball to whom?” He is the subject, whom is the object.


We also use objects for objects of a preposition, which is a location/time word: to him, above him, before him, after him, for him. Same applies to whom: “Do not ask for whom the bell tolls, it tolls for thee.” (Thee is an archaic pronoun in object form).

Passive vs. active (e.g. “I hit the ball” vs. “The ball was hit by me”)

In English, we always have the choice of arranging a sentence into the active voice or the passive voice. The active voice is when the subject does something. The passive voice is when something is done by the subject.


“I hit the ball,” is active.

“The ball was hit by me,” is passive.

My old Latin teacher used to call passive voice the politicians’ voice, because politicians use it to deflect responsibility. Instead of saying, “I made a mistake,” in the active voice, politicians say, “Mistakes were made,” in the passive voice. That way they don’t have to put themselves in the sentence.

In English, we always prefer the active voice unless there’s a good reason for using the passive voice. For example, if you’re writing a biography of Abraham Lincoln, you might write, “Abraham Lincoln was shot by John Wilkes Booth,” in the passive voice, to keep the focus on ole Abe.

Subject-verb agreement with group nouns and percentages (e.g. “My band plays every Sunday”).

English is, as mentioned, a lazy language. It mostly avoids conjugating verbs to agree with the subject. The only time it really does so is in the third person singular vs. plural.


“He goes to the movies.” That’s correct.

“They go to the movies.” That’s also correct.

When you have a group of people, it’s treated as singular, no matter how many there are. So:

“My group of friends goes to the movies.” This is correct. Notice here how the subject is group, not friends. That’s because friends is after the preposition “of”, and just describes the group.

“My friends go to the movies as a group.” Still correct. Now friends is the subject.


Slightly more advanced are percentages. Percentages aren’t groups; they represent multiple people. So:
“Half of my friends go to the movies,” is correct. It’s not half as a group, but instead describing a bunch of your friends going to the movies.

“Most of my friends go to the movies,” is also correct.


Necessary and unnecessary modifiers (that vs. which, and when to use commas)

In English, we often modify our words. See what I did there?

When we want to emphasize that our modifiers are necessary for understanding the meaning of the sentence, we often use “that” and we never place the modifier in commas.

When we want to emphasize that our modifiers are not necessary for understanding the meaning of the sentence, we often use “which” or a participle (-ing verb), and we always place the modifier in commas.

So, if you asked me which house is mine:
“I live in the house that has a red door.” This way, you can pick out my house.

“I live in the house with a red door, which I bought in 2015.” This way, you can pick out my house, and I also have given you a little extra information that doesn’t answer your question (you’re welcome).

Run-ons, fragments, independent clauses, and dependent clauses (when “and” isn’t enough)

Every sentence in English needs an independent clause. It can also have dependent clauses.

Independent clauses have a subject and a verb. Dependent clauses are lacking one of those. Independent clauses also just “sound right” on their own, while dependent clauses sound like a fragment.


“I went to the movies,” is a full sentence with an independent clause.

“I went to the movies, which were packed,” is a full sentence that includes a dependent clause (an unnecessary modifier.”

“I went to the movies and then to the car wash,” also works.

“I went to the movies; I never was so bored in my life,” works, but only because I separated the two independent clauses with a semicolon  . Even if I put “and”, it wouldn’t have been enough.

Parallelism (what to do after “and” or in a list)

The last difficult grammar concept is parallelism.

Parallelism is matching up the various parts of a sentence as closely as possible. We do that around a conjunction (short linking word, like “and”, “but”, “or”), in a list, or when making a comparison.


“I am a doctor and a lawyer,” is correct (and impressive), because those are two nouns connected by a conjunction.

“I am a practicing doctor and a retired lawyer,” is correct, because it parallels the adjective + noun structure.

“I practice law, medicine, and freelance therapy,” is correct (and likely unethical), because those are all nouns connected by a list.

“A lawyer in a courtroom is nothing like a therapist in a therapy session,” is correct, because those are two noun + prepositional phrase (in a courtroom & in a therapy session), which are being compared to each other.


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