Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
AGREEMENT, CONCORD
Grammars often use these terms interchangeably. Agreement or concord is required in Standard English mainly in two situations. (1) Subjects and verbs must agree in number. For most verbs this agreement (or concord) is a problem only with a singular subject and a third person singular present tense verb: he/she/it goes, but I, you, we and they go. In the past tense, both she and they went. Failure of agreement, particularly when subject and verb are close together, is a serious blunder, Substandard in both speech and writing. (2) Pronouns must agree with antecedent nouns in number, gender, and sometimes case, and failures in these agreements are also Substandard. Only the genitive case is distinctive in English nouns these days: Spot is Mary’s dog, her dog, hers; these are the children’s bikes, their bikes, theirs. In addition, the adjectives this and that must agree in number with the nouns they modify: this hat, these hats; that belief, those beliefs. See AGREEMENT OF INDEFINITE PRONOUNS AND OTHER SINGULAR NOMINALS WITH VERBS AND OTHER PRONOUNS.
