There are a number of reasons why structure is up there with melody and harmony as an important element in the successful composition of music. The most obvious reason is the need for a plan to enable the music to ‘hold together’ – to be cohesive and have unity. Students of subjects like History or English are taught how to structure essays so that there is a natural flow from the introduction through the main points and illustrations to a conclusion. Any building project from a model plane to a skyscraper has a set of blueprints so that the right pieces are put together in the right order or the relative dimensions are correct over a strong set of foundations. Painters will draw outlines and plan the positions of key parts of their painting on the canvas, writers will do storyboards and travelers about to embark on a journey will plan their route and work out timings and stopovers.
All music needs structure in order for it to make sense to the listener. It helps on a journey to see landmarks or towns so that we know where we are, or to be able to view the map with the little plane on it on long haul flights. Listeners subconsciously tap into familiar melodies or motifs, feel reassured when they hear something they have heard before, and get excited when the music builds up to a key moment. Structure gives music not only its shape but also its identity.
How is music structured?
There are many ways to structure a piece of music, some very common and some less obvious. Structures exist on a small and large scale; a melody will often have a phrase structure, a verse will have a melodic structure, a song will have a structure of verses and choruses, a symphonic movement will have a self contained structure but will also be part of the overall structure of the whole symphony.
Underlying most structures in music is the management of repetition and contrast. A lot of successful compositions will have a certain amount of material, made up of melodies, motifs, rhythmic patterns, chord progressions and so on, and these will be repeated, developed and varied with careful thought given to balance and interest.
Another concept that underlies a lot of structures is that of tonality. Often composers will use keys to shape their piece, perhaps beginning in the tonic key, moving to one or more related keys and returning to the tonic again. This is less common in popular genres where keys tend not to change apart from for effect, but in classical music as composers became more interested with eroding ‘traditional’ tonality from their music it was cohesion and unity that they found hard to maintain.