Latin's (and English's) case system goes back to Proto-Indo-European. There were special endings (case endings) attached to nouns to show how they functioned in a sentence. The system works the same as when we add “'s” to a word to show possession, but there were other endings to show many other functions. In the eyes of our linguistic forebears, there were eight different things a noun could do in a sentence, so there were eight different cases to show each of those eight things. (Remember, a case is just a certain group of letters at the end of a word.) Six of those things related to the verb. For example, one case showed that that noun was the subject of the verb. Other cases indicated that the action was going away from, toward, or alongside the noun. A fifth case identified a noun as the place where something happened, while a sixth case showed on whose behalf something was done. A seventh case linked two nouns together in a special relationship (like possession), and an eighth turned a noun into an exclamation (e.g., Gail!).

Latin condensed these original eight into five cases to show a noun's function in a sentence. Actually, Latin has seven cases, but you don't see one very often and the other is reserved for certain words. We will cross those bridges when we come to them.