Some pronouns have three forms in each number to denote differences in construction. They are therefore said to have three cases. The three forms are called the nominative case, the possessive case, and the objective case. Nouns have but two forms to show difference in construction; but for the sake of uniformity nouns also are said to have three cases. Thus the nominative and objective forms of nouns are alike. When a noun is used in a construction that requires the nominative form of a pronoun, it is said to be in the nominative case. When it is used in a construction that requires the objective form of a pronoun, it is said to be in the objective case.