The Syntax of Agreement and Concord

'Agreement' is the grammatical phenomenon in which the form of one item, such as the noun 'horses', forces a second item in the sentence, such as the verb 'gallop', to appear in a particular form, i.e. 'gallop' must agree with 'horses' in number. Even though agreement phenomena are some of the most familiar and well-studied aspects of grammar, there are certain basic questions that have rarely been asked, let alone answered.