The perils of approximate ontology

The mathematical centerpiece of many physical theories is a Lagrangian. So let’s imagine that there’s some Lagrangian we trust. Should that induce us to endorse an ontology? If so, what ontology, and how is it related to our trustworthy Lagrangian? I’ll examine these questions in the context of quantum field theoretic Lagrangians. When these Lagrangians are understood as “merely effective,” a variety of approximations figure in the physics they frame. So do distinctive grounds for trusting those Lagrangians, grounds recent literature has adduced in support of a novel variety of scientific realism known as Effective Realism. This essay attempts to undermine those grounds, and to do so without presupposing extensive prior knowledge of quantum field theories.