You may feel confident with the most commonly tested grammar rules on the GMAT Sentence Corrections - subject-verb agreement, verb tense, pronoun reference, pronoun number, misplaced modifiers, parallelism, idioms, false comparisons, and quantities. It’s hard to imagine any other grammar rules that could possibly be tested, but you can bet the GMAT test writers are pretty exhaustive. Here are four grammar rules that don’t receive as much attention; you’ll need to master these if you’re going for a top score.
1. Subjunctive Mood
You won’t see the subjunctive mood tested on college entrance exams like the SAT and ACT; it’s purposely reserved for the GMAT for good reason. Most of the English verbs we use are in the indicative mood - that is, verbs that have happened, are happening, or will happen. The subjunctive mood is used to express wishes or possibilities that have not happened.
The most common subjunctive verb that you might encounter is were, the subjunctive form of was.
Example 1: If he were athletic, he could make the football team. (He is not actually athletic, so the verb communicates an idea that does not really exist).
Notice that “If he was athletic…” would be incorrect, even though you may not reconize such an error in speech or writing.
Example 2: The teacher requires that you be present on the final day of class.
The indicative conjugation would be “you are present,” but since “requires” triggers the subjunctive mood, we use be.
Example 3: She recommended that each student bring his or her homework every day.
The indicative conjugation would be “each student brings,” but since ‘recommended’ triggers the subjunctive, we use bring.
Notice that these verbs are often followed by subjunctive clauses:
Ask, demand, insist, order, prefer, recommend, request, require, suggest, wish
2. Possessives
The GMAT sometimes tests the difference between a possessive and a contraction. While this may sound simple to some of you, the distinction can be expectedly confusing. After all, its is the possessive of it, and it’s is the contraction of it is. That’s right, its is a possessive, and it lacks the requisite apostrophe.
Example 1: When our home computer lacks its virus protection, it’s more vulnerable to infection.
3. Split Infinitives
The rule of the split infinitive may be the ultimate nitpicky grammar rule, but it is still a rule you should know. Simply put, when writing an infinitive verb (e.g. to go), do not place any word in between “to” and the verb (e.g. to boldly go). Perhaps the most eye-opening example of a split infinitive is from the opening of Star Trek: The Next Generation:
Example 1: Its five year mission: to boldly go where no man has gone before. (As long as we’re studying grammar, you should probably also notice that this sentence is a fragment.)
Example 1, corrected: Its five year mission is to go boldly where no man has gone before.
Note that the split infinitive error will probably not be the main error in a sentence, but you can be confident that a sentence with a split infinitive is usually incorrect.
Since these rules don’t constitute the majority of the sentence corrections, I’d study them last. Knowing them will help you pick up some valuable extra points.