English sentence structure allows for both compound subjects -- more than one subject described by a single predicate -- and also for compound predicates, in which multiple predicates refer to one or more subjects. Since compound subjects may contain both single and plural forms, some variations in subject-verb agreement may occur in these sentences.
Subjects and Predicates
The subject of a sentence can be a noun (common or proper) or pronoun: "Mary went shopping;" "She bought milk." The subject designates the main focus of the sentence and the performer of actions described by its predicate. The predicate consists of a verb and all elements associated with it, such as prepositional phrases, adjective phrases and adverbs: "Juan took an advanced math class;" "Sharon was glad to see her mother." The predicate comments on and completes the subject.
A subject may be expressed by multiple nouns connected by the conjunctions "and" and "or:" "Steve and Mary went to dinner at a fine restaurant;" "Either Miko or Sachiko wrote the letter;" "John, Peter and Aaron play varsity football." In these sentences, the verb expressed by the predicate applies to all members of the subject.
Compound predicates can apply to simple and compound subjects: "Rachel washed the dishes and went to bed," "Rachel and her sisters cleaned the kitchen and put everything away." Elements of a compound predicate can be joined by the conjunctions "and," "or" and "but:" "Jackie registered for the class but dropped it;" "Claire got up early and went for a run."
Compound Subject-Verb Agreement
When compound subjects contain both a singular and a plural element joined by "and," present tense verbs are plural: "Anna and Mary study Spanish together." But when compound subjects are joined by "or/nor," rules of agreement state that a present-tense verb in the predicate must agree with the element closest to the verb: "Either the counselor or the campers take a hike every morning." "Neither the students nor the teacher has a calculator handy."
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