There are special verb endings for the dual as well, but only in the 2nd and 3rd person. Nouns, pronouns, adjectives and the article in Ancient Greek also change according to their function in the sentence. For example: These different forms are called different cases of the noun. The four principal cases are called the nominative (Subject), genitive (of), dative (to, for, with), and accusative (direct object). In addition, some nouns also have a separate vocative case, used for addressing a person:  Frequently a vocative is preceded by the word () "o". Where there is no separate vocative case (which is the case for all plural nouns), the nominative is used instead. The order in which the cases are given differs in American and British textbooks. In American grammars, such as H. W. Smyth's "Greek Grammar" (1920), the order is Nom. - Gen. - Dat. - Acc. - Voc.; in grammars produced in Britain and countries formerly under British influence the order is Nom. - Voc. - Acc. - Gen. - Dat. The accusative, genitive, and dative cases are also used after prepositions, for example:  Usually prepositions which mean "towards" such as () are followed by a noun or pronoun in the accusative case, while those that mean "away from" are followed by one in the genitive. Some prepositions can be followed by more than one case depending on the meaning. For example, () means "with" when followed by a noun in the genitive, but "after" if followed by an accusative. Nouns differ as to their endings. For example, the nominative plurals of regular masculine and feminine nouns can end in (), () or (). They are divided into three different groups, called declensions, according to these endings and the endings of the other cases:  1st declension nouns tend to be feminine (but there are some exceptions such as () "a soldier"), 2nd declension nouns tend to be masculine (again with exceptions). Neuter words in the nominative and accusative plural have the endings () or (). They are divided into the 2nd and 3rd declensions according to the endings of their genitive and dative cases, which are the same as those of masculine nouns. Neuter nouns also differ from masculine and feminine nouns in that they do not have a separate ending for the accusative case, but the nominative, vocative, and accusative are always identical.