Often times when I start writing a piece, I’ll put it in a comfortable key, with the idea that when I’m comfortable with the piece, I can adjust up or down into the right key.
The problem is this: the key has an opinion. If I’m writing in E-flat, my melodic contours will be shaped by the key and the comfortable tessitura of singers/range of instruments. I won’t be able to change it, much, afterwards.
There are many mysteries to live with in composition – sometimes you’ll play back discoveries and have no sense of being the creator of them – it doesn’t feel as if you’ve imposed the order, but that the order has come to you. In the list of mysteries is the key – and how it can have an opinion that shapes the evolution of your piece.