Relative newbie here. I'm sure this discussion has taken place here before, and I've read many of the discussions that cover this more broadly (i.e. "How do you come up with your ideas?" etc.) but I'm interested specifically in various themes within a musical form.
My specific example. I decided recently that I'd like to write a cello sonata. I began mapping the piece out: the form (sonata for the first movement), rough length, what I'd like to convey, and some of the organizing and unifying structural principles. However, now it's time to construct the themes which will fit into that structure and I am absolutely stuck. There's something I'm looking for and I can sort of see it, but can't quite reach it.
So I'm curious how other composers create their thematic material. Do you mostly improvise? Do you draw out the shape of the theme first and then decide on the notes? Do you just write *something* and then revise and change it until you have a theme you want to use?
I look forward to your responses.