LEARN NOT TO SPEAK ESPERANTO
Justin B Rye [MAIL] 1997–2002

Ranto Appendix – R

CASE

A good polyglot learns to take the rules of any given target language for granted as natural laws; a good linguist on the other hand learns that there are many different ways of doing things.  Esperantists (who tend to be hobbyist Euro-polyglots) often trumpet the language's case-marking system as an indispensable guide to the fundamental argument structure of a sentence.  But even disregarding the way Esperanto mixes indirect objects in with its direct objects, there's nothing logically necessary about subjects and objects.  Indeed, the terms are only meaningful once you've defined them for a specific language in terms of the more universal concepts of:

Different languages group these according to various schemes.

A) the pedant's solution (known from one Australian language).  Clearly more complicated than there's any call for.

Agent distinguished as Ergative case
Experiencer distinguished as Intransitive case
Patient distinguished as Accusative case

B) the clairvoyant's option (less rare; much use of context): cases not distinguished even by wordorder rules.

AgentExperiencerPatient all treated alike (i.e. no cases)

C) the monster raving loony candidate (some Iranian sightings); combines all the drawbacks of (A) and (B).

AgentPatient treated alike as Transitive case
Experiencer distinguished as Intransitive case

D) the orthodox Indo-European approach; two cases, Nominative (= Nonpatient) versus Accusative (= Patient).

AgentExperiencer treated alike as Nominative case
Patient distinguished as Accusative case

(In English, for instance, Nominatives go before the verb and Accusatives after.)

E) looking glass logic – the rather widespread opposite of (D); Agent versus Nonagent.

Agent distinguished as Ergative case
ExperiencerPatient treated alike as Absolutive case

(This often strikes Europeans as passive: sentences hinge on the Absolutive – often meaning the Patient – not the Ergative; cf. Sam was seen by us.)

F) a compromise solution – part (D), part (E).  Also common.

Agent ⁄ (voluntary) Experiencer handled as Nominative case
Patient ⁄ (involuntary) Experiencer handled as Absolutive case

(So in I slid on the ice, I may be Nominative if it was deliberate skating or Absolutive if it was an accident.)

What's more, many languages mix the above systems!  For more detail, and further examples of exotic possibilities Zamenhof never considered, see Language Universals and Linguistic Typology by Bernard Comrie.