[question] about the active, passive and middle voice

[julitoprincipito]

I am writing a thesis on the three common voices and I find some interesting yet difficult circumstances.

eg. The cloud floats on the sky.

Is this sentence active or middle? The cloud is apparently not the agent, nor is it the patient I suppose. Yet neither does it belong to the 'common' middle voice like 'the water boils' or 'the rice cooked well'...since in the latter two sentences we can easily tell the 'water' and the 'rice' are the semantic patients, but in the former sentence the 'cloud' isn't. So i'm puzzled.

 

Similar things happen in Korean, which even seems a bit funny, cuz in Korean, the verb 'float'(tteu-da) is an intransitive verb, but it has a passive form(tteu-i-da)! And there are still more such examples in Korean, a freaky language where intransitive verbs also have passive forms...

 

How in the world should we define the terms 'active' 'passive' and 'middle'? The core difference lies in whether the subject is an agent or not, or it depends on some other conditions??

 

All forms of discussion are welcome!

[lzs]

It seems to me that "The cloud floats on the sky" is active (though I'd probably say "in the sky" rather than "on the sky," so maybe we have different dialects). Since active voice does not require the presence of an agent or a patient, I don't see why the cloud being neither of those would be a problem.

[this_is_a_wug]

In case you haven't already seen, WALS has a great chapter on this: 

 

http://wals.info/chapter/107