What I want to do here is restart the discussion by looking at form from an entirely different angle. In the previous post I talked about the basic structure of songs as that is something many people are familiar with. Today I want to take a different tack. There are three fundamental aspects of music: melody, harmony and rhythm. Every piece of music is a structure in which any one, two or all three are present--even John Cage's 4'33 which has a structure consisting only of rhythm, i.e. time. The form of a piece of music, that is, the articulation of it in time, is created by using any one, two, or all three of these aspects. That is so abstract that you are probably either scratching your head or rolling your eyes! Let me make it more concrete.
Let us imagine a simple musical context: a drumming circle. In Montréal when I lived there a group of drummers used to meet on Sunday afternoons in the park and drum together. Someone would start a simple beat then others would add various subdivisions and syncopations of the beat until a satisfactorily dense texture was created. This might go on until everyone was tired of it and then stop. Or, if it started to flag, someone might try and start an entirely new pulse, thereby launching a new section. If this just goes on until it peters out, then you have the form A (the first beat) followed by B (the second beat). If everyone then went back to the first beat then the form would be ABA. This is the very simplest musical form. Do something, then do something else, and if you are clever, then you return to the first thing again.
But the very first kinds of written down music in the West are both more complex than this but also even simpler. One of the earliest kinds of music in the West consisted of singing the psalms. Singing made the text a more sacred utterance. One person would first sing a few notes to establish the pitch, this is an "intonation", then the rest join in on a "reciting tone", just a repeated note. This reciting tone can go on as long as needed for the text. It can be punctuated if needed to indicate a division in the text. This punctuation was called a "fluxus". Then you return to the reciting tone. To end, there is another few notes that fall in pitch, called a "cadence" which means falling or "cadere" in Latin. Don't mix this up with the cadence in common practice harmony, which refers to a structure of two or more harmonies.
I suppose that what I have just described is very roughly ABA, but it is really a kind of musical prose, where the form is very loose and while originally there is just enough melody to encourage people to sing a text, the tendency over time is to add more and more decoration. Here is an example of this kind of psalm setting, one of the early favorite texts "Justus ut palma" from Psalm 91:
This kind of form is so loose that it is almost impossible to describe. A lot of music composition consists in giving form to what was originally formless. So a meandering melody like this, only organized in terms of a reciting tone and a final tone, composers are going to replace with a melody with a clearer structure. I'm not going to work my way through music history here, instead, I'm just going to jump to a different kind of melody that is very organized. Here is the original subject from the Art of Fugue that Bach will transform in various ways:
You will notice that as each voice enters, it does so with the same theme. This is one way of structuring a piece of music with melody. Though, of course, as soon as you have more than one voice, then the harmonic structure becomes hugely important as well. But let's leave that aside for the moment and just note how this simple melody ties the whole piece together. You can look at the structure of fugues in various ways, but the most salient aspect is that theme: it is what generates the structure, that is, the form.
In a more mechanical way, the contemporary composer Steve Reich has done something very similar: use a single theme to generate the structure of a piece. He does it by creating a short theme for piano and then, with two pianos playing that theme together, one "slides" ahead rhythmically bit by bit, a process he calls "phasing". Here is what that sounds like:
UPDATE: Here is a complete version of the piece:
In between the basic subdivisions, i.e. when the notes don't "line up", there is considerable rhythmic tension that is released when the two pianos slip back into alignment, though, a different alignment! The piece ends when the whole set of alignments has been traversed and the two pianos are back in the original relationship.
What is interesting about this is that he uses only a simple rhythmic device to generate the whole piece from that original theme.
There is a lot more to say about how musical form can be created, but I'll save it for next time!