A structure can be very useful, but also very constraining.
Personally, I form an idea of the whole piece once I’ve started it, but before thinking about structure I need to get the general feeling of it.
It’s like looking at a landscape through the fog: you can’t see the contours clearly, but you get the idea of it.
Often, if you just let youserlf go,
you’ll land in places where you could have never landed
if you were trying to fill in the blanks of a superimposed structure.
Generally speaking, I start thinking about a structure when I hit a wall in the flow and I realize I need to go back to some material in order to make a point come through. That’s when structure and craftmanship comes in handy.
Piece of advice: there’s no need to reinvent the wheel: study great composers of the past, constantly.
What they did, worked. For a reason.