Marilynne Robinson's favourite genre

Oddly enough, my favorite genre is not fiction. I’m attracted by primary sources that are relevant to historical questions of interest to me, by famous old books on philosophy or theology that I want to see with my own eyes, by essays on contemporary science, by the literatures of antiquity. Every period is trapped in its own assumptions, ours, too, so I am always trying, without much optimism, to put together a sort of composite of the record we have made that gives a larger sense of the constant at work in it all, that is, ourselves. The project is doomed from the outset, I know. Still.