For reference, here are the declensions of the definite article and three typical nouns, one masculine, one feminine, and one neuter. Note that the masculine and neuter nouns and definite articles have several similarities.
|nominative||ὁ ἄνθρωπος||οἱ ἄνθρωποι|
|genitive||τοῦ ἀνθρώπου||τῶν ἀνθρώπων|
|dative||τῷ ἀνθρώπῳ||τοῖς ἀνθρώποις|
|accusative||τὸν ἄνθρωπον||τοῦς ἀνθρώπους|
|nominative||ἡ φωνή||αἱ φωναί|
|genitive||τῆς φωνῆς||τῶν φωνῶν|
|dative||τῇ φωνῇ||ταῖς φωναῖς|
|accusative||τὴν φωνήν||τὰς φωνάς|
|nominative||τὸ ἆθλον||τὰ ἆθλα|
|genitive||τοῦ ἄθλου||τῶν ἄθλων|
|dative||τῷ ἄθλῳ||τοῖς ἄθλοις|
|accusative||τὸ ἆθλον||τὰ ἆθλα|
In very old Greek, such as the Iliad and the Odyssey, another number, the dual, was used to refer to pairs of objects. It was little used in most classical Greek.
Vocative case was used less and less as time went on. It and dative have disappeared and are not used in modern Greek.