English has largely lost its case system although personal pronouns still have three cases, which are simplified forms of the nominative, accusative and genitive cases. They are used with personal pronouns: subjective case (I, you, he, she, it, we, they, who, whoever), objective case (me, you, him, her, it, us, them, whom, whomever) and possessive case (my, mine; your, yours; his; her, hers; its; our, ours; their, theirs; whose; whosever). Forms such as I, he and we are used for the subject ("I kicked the ball"), and forms such as me, him and us are used for the object ("John kicked me").
Languages such as Sanskrit, Ancient Greek, Latin, Armenian, Hungarian, Hindi, Tibetan, Czech, Slovak, Turkish, Tamil, Romanian, Russian, Polish, Croatian,Serbian, Estonian, Finnish, Icelandic, Belarusian, Ukrainian, Lithuanian, Basque and most Caucasian languages have extensive case systems, with nouns, pronouns, adjectives, and determiners all inflecting (usually by means of different suffixes) to indicate their case. The number of cases differs between languages: Esperanto has two; German and Icelandic have four; Turkish, Latin and Russian each have at least six; Armenian, Czech, Polish, Serbo-Croatian, Ukrainian and Lithuanian all have seven; Sanskrit has eight; Estonian has fourteen and Finnish has fifteen, Hungarian has eighteen and Tsez has sixty-four.
Commonly encountered cases include nominative, accusative, dative and genitive. A role that one of those languages marks by case is often marked in English with a preposition. For example, the English prepositional phrase with (his) foot (as in "John kicked the ball with his foot") might be rendered in Russian using a single noun in the instrumental case or in Ancient Greek as τῷ ποδί (tôi podí, meaning "the foot") with both words (the definite article, and the noun πούς (poús) "foot") changing to dative form.
More formally, case has been defined as "a system of marking dependent nouns for the type of relationship they bear to their heads".:p.1 Cases should be distinguished from thematic roles such as agent and patient. They are often closely related, and in languages such as Latin, several thematic roles have an associated case, but cases are a morphological notion, but thematic roles are a semantic one. Languages having cases often exhibit free word order, as thematic roles are not required to be marked by position in the sentence.
The English word case used in this sense comes from the Latin casus, which is derived from the verb cadere, "to fall", from the Proto-Indo-European root *ḱad-. The Latin word is a calque of the Greek πτῶσις, ptôsis, lit. "falling, fall". The sense is that all other cases are considered to have "fallen" away from the nominative. This picture is also reflected in the word declension, from Latin declinere, "to lean", from the PIE root *ḱley-.