Hi Anon,
I'm fascinated by the subject, though uneducated in it's linguistic applications.
Pitch recognition, like color recognition, is a mysterious phenomenon. Most "western" musicians consider it rare, possibly genetic, or inborn. Some are envious of those who have that strange ability, but some who have it consider it a curse. I've only known a handful of them personally.
A couple of years ago I read of a study involving some Asian population, in which adult native speakers were recorded, speaking a number of typical phrases in their native tongue. A month later the same subjects repeated the process, and it was discovered that without exception the pitches of the intonations were identical to the originals. It was concluded that this "sense" of pitch recognition, or repeatability, is learned. However, further investigation showed that it must be learned as a child. That is, a westerner could not move to an Asian country as a teenager, become immersed in the language, and acquire this ability. This is something of a revelation.
My point is that I realize the significance of intonation to a westerner is extremely different from what it is to those who have grown up in Asian countries - at least in some of them.
I believe that CJ and Kooyeen are well versed in all aspects of the sound of English, including intonation, and would be qualified to comment on the usefulness of a four- or five-level system of pitch analysis. You correctly understood my remarks about a given sentence being spoken with varying intonations as the circumstances change. I gather this is different in your native language.
As an aside, I wonder if you can tell me how teenage males deal with the problem of the changing voice. Are the four tones strictly relative and unique to the individual, or do all people of a common voice range share the same four tones?
Best wishes, - A.