In grammar, the accusative case is the form that a noun, pronoun or adjective in an inflected language takes when it is the direct object of a transitive verb. To put that in layman's terms, sometimes words are spelled differently depending on their role in the sentence. These systematic spelling variations are referred to as a word's cases. The subject — usually the person or thing that is acting in the sentence — takes the nominative form, while the direct object — the person or thing that is having something done to it — takes the accusative form. In some languages, the accusative case might have other uses as well, but these vary greatly from language to language.
In many languages, including Esperanto, Greek, Latin, Polish, and Sanskrit, subjects and direct objects have different forms or spellings. These languages are known as inflected languages. For instance, Latin first-declension nouns in accusative case end in -am in the singular and end in -as in the plural. Regardless of where the word is found in the sentence, those endings alert the reader or hearer that that word probably is the direct object. Adjectives or articles that modify the direct object and any pronouns that function as direct objects in these languages usually must also be in the accusative case.
Most inflected languages have more than just the nominative and accusative cases. Often, several different cases, including the accusative, can be used as the object of certain prepositions or to express various other relationships. German, for example, uses the accusative case in certain temporal clauses. In Greek, there might be no easily apparent reason why a object of a particular preposition takes the accusative case rather than the genitive or dative case. When learning a new language, these uses must often simply be memorized or acquired through repeated exposure.
Modern English, on the other hand, does not have a fully formed case system, so it has no true accusative case. The spelling, or morphological form, of an English noun usually does not change depending on whether it is a subject or direct object. For example, both of the nouns in the sentence "Maria likes giraffes" are spelled the same way as the nouns in the sentence "Giraffes like Maria."
A few English pronouns will change their forms when used as objects; for example, "he" becomes "him" and "she" becomes "her," depending on their function in the sentence. These pronouns are sometimes said have an objective case or oblique case, which is similar to the accusative case of other languages. Labeling the case of a pronoun in English is useful when discussing the difference between "who" and "whom" or other potentially confusing grammatical situations.