Picturing Feynman Diagrams and the Epistemology of Understanding

In this paper, I take up the following puzzle: If Feynman diagrams represent states of affairs, but do not do so truthfully what can their epistemic value be? I argue that Feynman diagrams have been epistemically powerful (at least in part) because, as pictorial representations, they facilitate an understanding of quantum electrodynamics, and quantum field theories more generally. Drawing on Richard Feynman's own remarks and Catherine Z. Elgin's account of the role of understanding in science, I tease out what it might mean to have an understanding of something that is not factive. Although my approach allows for a thin sense of substantively non-factive epistemic success, it is continuous with a factive sense of understanding that is more familiar in the sciences.