The concept of grammatical case is difficult to explain. To say that case refers to a system of endings for nouns that reveal a noun's function in a sentence is not especially satisfying. When English was a highly inflected language (i.e., one that relied on endings rather than word order), cases were abundant. In modern English, we are left with only one case for nouns and three for pronouns. That one surviving noun case in English is the genitive case. It refers to the ending “'s” (or “s'” in the plural) to show one noun's possession of another, as in “Donna's garden.”