Subjects and verbs must agree. The 'subject' of a sentence is the noun to which the verb in the sentence's main clause refers, and the two must always agree in number: singular subjects must be paired with singular verbs; and plural subjects, with plural verbs. Though it may sound simple, the GMAT uses tricky constructions and phrasings that make these questions seem far more complicated than they actually are.

Test writers will try to fool you by writing unusual phrases that make it difficult to tell if the subject is singular or plural. Below, you'll find a list of rules and tips for subject-verb agreement that will assist you in making sense of the GMAT's intentionally confusing questions.

1. What "Agreement" Means in English Grammar
The "Agreement" rule dictates that corresponding parts of a sentence must match – "agree with" – one another. What exactly does this mean? If you've ever studied a foreign language, like French or Italian, then you're already familiar with the concept of agreement: when you change the form of a word to make it fit properly into the sentence, like changing the ending of a masculine adjective to feminine because the noun it modifies is feminine –- that's agreement. Agreement allows us to show who's doing what in a sentence in a clear and unconfusing manner. Without such a method of clarification – of indicating which adjectives in a sentence modify which nouns, or which nouns are governed by which verbs – clear expression, in writing and speech alike, would be very difficult.

Because English is structured differently than French or Italian (or Spanish or Polish or Latin, etc etc), the changes you have to make in order to adhere to the rules of agreement will be different. But the basic concept – of assuring a "match in form" between corresponding parts of a sentence - is the same.

2. Kinds of Agreement
In the English language, agreement applies to several different kinds of pairings: nouns and their verbs; pronouns and their verbs; adjectives and the nouns they modify; prepositions and the verb(s) they govern. Depending on the nature of the pairing, agreement may be required in terms of tense, number, or case. Tense and number apply to verbs; number applies to verbs, nouns, and pronouns; and case applies to nouns, pronouns, and modifiers:

Tense: indicates when an action happened, is happening, or will happen
Number: indicates "how many" - singular (one) or plural (more than one)
Case: indicates role of noun or pronoun in sentence. In English, nouns only change form for the possessive case, while pronouns have different forms for the possessive, subjective, and objective cases.

Agreement requires that corresponding parts of a sentence match in as many of these ways as possible: for example, a noun and verb can agree in terms of number (singular or plural) only, while a noun and a pronoun can agree in terms of both number (singular and plural) and case (possessive or otherwise). For native English speakers, agreement is for the most part instinctive, presenting little difficulty in simple constructions: singular nouns agree with singular verbs, plural nouns with plural verbs, and so forth.

But more complex sentences - those containing several nouns, verbs, and/or pronouns – can sometimes make even the simplest applications of agreement confusing.

3. Agreement in Action
In order to apply agreement rules, you must be able to recognize when agreement is required: what parts of the sentence are "corresponding parts"?

Because a sentence can contain more than one noun and verb, subject-verb agreement helps to clarify which noun is the subject, and by which verb it is governed. Refer to the main chapter for help on recognizing and correcting subject-verb agreement errors on the GMAT.

Seven Types of Errors

B. Subject/Verb Separation