Originally the Indo-European family of languages, to which Latin belongs, had at least seven case-forms, besides the Vocative. But in Latin the Locative and the Instrumental were lost[Some of the endings however, which in Latin are assigned to the dative and ablative are doubtless of locative or instrumental origin (see p. 34, footnote).] except in a few words (where they remained without being recognized as cases), and their functions were divided anuong the other cases.
The Nominative, Accusative, and Vocative express tbe simplest and perhaps the earliest case-relations. The Nominative is the case of the Subject, and generally ends in -s. The Vocative, usually without a termination, or like the Nominative (§38 a) perhaps never had a suffix of its own.[The -e vocative of the second declension is a form of the stem (§45. c).] The Accusative, most frequently formed by the suffix -m, originally connected the noun loosely with the verb-idea, not necessarily expressed by a verb proper, but as well by a noun or an adjective (see §386).
The Genitive appears to have expressed a great variety of relations and to have had no single primitive meaning; and the same may be true of the Dative.
The other cases perhaps at first expressed relations of place or direction (To, From, At, With), though this is not clear in all instances. The earlier meanings, however have become confused with each other, and in many instances the cases are no longer distinguishable in meaning or in form. Thus the Locative was for the most part lost from its confusion with the Dative and Ablative, and its function was often performed by the Ablative, which is freely used to express the place where (§421). To indicate the case-relations - especially those of place - more precisely, Prepositions (originally adverbs) gradually came into use. The case-endings, thus losing something of their significance, were less distinctly pronounced as time went on (see §36, phonetic decay), and prepositions have finally superseded them in the modern languagcs derived from Latin. But in Latin a large and various body of relations was still expressed by case-forms. It is to be noticed that in their literal use cases tended to adopt the preposition and in their figurative uses to retain the old construction. (See Ablative of Separation 402 - 404; Ablative of Place and Time, §421 ff.)
The word casus, case, is a translation of tbe Greek ptwsis, a falling away (from the erect position). The term ptwsis was originally applied to the Oblique Cases (§35. g), to mark them as variations from the Nominative, which was called orjh, erect (cásus réctus) The later name Nominative (cásus nóminatívus) is from nomino, and means the naming case. The other case-names (except Ablative) are of Greek origin. The name Genitive (cásus genetívus) is a translation of genikh [ptwsis], from genos (class), and refers to the class to which a thing belongs. Dative (casus dativus, from dó) is translated from dotikh, and means the case of giving. Accusative (accusativus, from accuso) is a mistranslation of aitiatikh, (the case of causing), from aitia, cause, and meant to the Romans the case of accusing. The name Vocative (vocátívus, from voco) is translated from klhtikh (the case of calling). The name Ablative (ablátívus, from ablatus, aufero) means taking from. This case the Greek had lost.