WRITING TO DISCOVER
To write an essay or—even more—a sonnet is an act of discovery or evocation. It is an attempt (the literal meaning of essay) to reveal what you don’t yet know you have to say, which emerges as you write—to your surprise and delight, if all goes well.
In expository, as distinguished from creative writing, you do know in advance at least the gist of what your composition will elaborate and clarify; but creative writing finds out as it proceeds what it will become.
There is no Muse for expository prose because there is no mystery to be fathomed, no Ah-Ha! to happen as when composing a poem or an essay. The motto for such creative endeavors is not so silly as it sounds: “How do I know what I think till I see what I say?”