If you are asking about the vocative, or "calling" case, it is used by inflected languages for direct address. In Latin, for example, the word lord is dominus for the nominative subject of the verb, as in Dominus vobiscum ( the lord is with you ), and domine for the vocative of address, as in Non nobis, Domine ( not to us, O Lord). The different endings on the words do for Latin what word-order does for English, which is to show who does what to whom.