In this talk, Bursten uses examples from classical physics and nanoscience to argue that in many physical systems, factors besides the natural laws occupy essential roles in explanation. While extra-nomological factors have long been recognized as elements of scientific explanations (e.g. as Hempel’s so-called “determining conditions”), most philosophical work on physical explanations has focused on the roles of law-like regularities and/or the cause–effect relationship in generating satisfying explanations of physical phenomena. Bursten focuses instead on the epistemological role of a particular sort of configurational constraint, namely the boundary
conditions on boundary  value models in physics, to show that these extra-nomological factors play at least three sorts of irreducible roles in physical explanation: (1) they suppress information about differences of configuration that don’t make a difference to the physical explanation of the system, (2) they describe what Cartwright has called “causal powers,” and (3) they constrain what Winsberg has called the “handshakes” between different physical theories that underwrite multi-scale modeling and explanations of multi-scale phenomena.