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:
- Agent = “Subject” of a transitive verb (“WE saw Sam”)
- Experiencer = Argument of an intransitive verb (“WE waited”)
- Patient = “Object” of a transitive verb (“Sam saw US”)
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.
| Agent ⁄ Experiencer ⁄ Patient | all treated alike | (i.e. no cases) |
C) the monster raving loony candidate (some Iranian sightings); combines all the drawbacks of (A) and (B).
| Agent ⁄ Patient | treated alike as | Transitive case |
| Experiencer | distinguished as | Intransitive case |
D) the orthodox Indo‐European approach; two cases, Nominative (= Nonpatient) versus Accusative (= Patient).
| Agent ⁄ Experiencer | 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 |
| Experiencer ⁄ Patient | 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… well, I used to cite an old favourite language typology textbook here, but I should probably be pointing people at the World Atlas of Language Structures.