Interpretive strategies for deductively insecure theories: The case of early quantum electrodynamics

• Early QED presents a case where reasoning strategies going beyond the deductivist “received view” of theories were successful.
• These strategies were not purely instrumental but provided more than merely empirical information about the world.
• In some circumstances these strategies may be more reliable than the received view and thus could be used even for contemporary theories.

I describe some interpretive strategies used by physicists in the development of quantum electrodynamics in the 1930s and 1940s, using Wimsatt's account of how to reason with false models as a guide. I call these “interpretive” strategies because they were used not just to derive empirical predictions, but also to derive information about the world besides the aforementioned predictions. These strategies were regarded as mathematically unrigorous, yet they were crucial to the development of a better theory of quantum electrodynamics. I argue that these strategies are not easily assimilated into conventional axiomatic, deductivist views of what theories tell us about the world. Furthermore, it is unclear if these strategies are necessarily less reliable than strategies based solely on mathematically rigorous inferences. I suggest that these less than fully rigorous strategies are worth considering as general strategies for working with theories in physics.