“Men see apostles,” and “Apostles see men”: two simple sentences with the same words. In English, word order tells who is seeing whom, but in Greek, word order does not distinguish subjects and objects. That is the function of inflection (word change) of Greek nouns. The pattern of inflection of a noun is called a declension.
In Greek, grammatical relationships are indicated by particular suffixes applied to the nouns. If a noun is the subject of a verb, it must, in Greek, be put into the nominative case with the appropriate suffix. If it is the object of a verb, Greek puts it into the accusative case. Thus “Men see apostles” would be
Greek has four basic cases: (1) the nominative, representing the subject (“Men see apostles”); (2) the genitive, representing the possessor (“The wisdom of men”); (3) the dative, representing the indirect object (“He gave gifts to men”); and (4) the accusative, representing the object (“Apostles see men”).