I know the basic distinctions of polyphonic/homophonic/heterophonic/monophonic, but I would be interested in either a formal attempt to describe how to distinguish one from the other, a more fine-grained description of differences in musical texture, or an exploration of the range of textural possibilities that falls within each of these "basic" types of texture. Do you know of any online/print resources that explore this topic, or do you have any ideas?
It's all to do with how much independence each of the voices has. Your lineup pretty much goes from most independence to least, although homophony and heterophony might be swapped around. JS Bach is a prime example of polyphony. If I really wanted to generalize, Bach is more polyphonic and Handle more homophonic. Handel loves a beautiful melody, especially in his vocal works, and often gives chordal accompaniment, which is regarded as more homophonic.
Heterophony is perhaps closer to monophony in that it is basically one melody or voice, accompanied by some sort of variation on that voice. Good examples can be found in Britten's Church Parables. Monophony is self explanatory and the easiest to recognize.
Gosh, it's hard to be that specific, sorry. In a truly contrapuntal piece like a Bach fugue, each voice is fully independent (at any given time) and interesting, so maybe an 8. In a homophonic piece the top voice is the most interesting usually, with the other voices rhythmically linked or subservient, but not using the same notes as they give harmony, so maybe a 4 or 5?. With heterophony there is little independence of the voices, as they are directly linked in shape and pitch, so maybe a 3?
In homophonic music, the voices tend to move mostly together rhythmically. Sometimes, one voice will have more movement, but as all the voices change the harmony together, this shows their interdependence. Thus the harmony moves in a "vertical" column and is fairly easy to analyze. This is easy to see in a lot of classical piano sonatas. The LH harmony and RH melody might each have some melodic interest, but both are forming the melody w/ harmonic accompaniment and move together.
In polyphonic music, the voices move independently, both melodically and rhythmically. Polyphonic music can be as simple as a kids' round (think Frere Jacques or Row, Row, Row Your Boat) or as complex as a 6-voice Bach fugue. The focus is more on the melodic nature of the lines rather than the vertical harmonic structure. Harmony exists, but it happens in passing based on how the different voices create consonance and dissonance with each other as they interact. Polyphonic music is analyzed more in regards to where the melodic material is repeated in the different voices, and the harmonic structure has more to do with large sections of the piece than with individual chords.