What is writing if not an a priori exercise? An exercise of the brain, that is. Not directed at truth, itself. Instead a working out of internally imagined consistency. A novel might reflect a sort of truth, maybe, but I don’t think that that is its aim.
Whereas the traditional a priori task of philosophy was to sort out Truth. Or truths. Accomplishing this via armchair reasoning. Thinking your way into Truth.
I doubt this can be done. Science with its empirical, social process is a better avenue into a form of provisional truth. Truth as close as we are going to get to it. Theories generally agreed upon, always subject to revisions.
That’s fine. Suits me. Better than an illusion of revealed or eternal Truth.
But fiction writing nonetheless is a mode of the older a priori method. A person alone in a room thinking. Thinking thoughts that don’t necessarily purport to be truth, but are themselves internally consistent – if the writing is any good. In this, it is more a philosophical than a scientific exercise, although certainly there is a degree of experiment involved. But not one socially agreed upon, unless you are a far too enthusiastic participant in a writing group.
How, then, to get to the “truth” of writing …? I leave that as an exercise for the reader, and myself.