On Various Senses of "Conventional" and Their Interrelation in the Philosophy of Physics: Simultaneity as a Case Study

My aim in this paper is to disambiguate various senses of "conventional" that in the literature have been often conflated. As a case study, I will refer to the well-known issue of the conventionality of simultaneity in the special theory of relativity, since it is particularly in this context that the above mentioned confusion is present. My pian is to start by sketching Reichenbach's originai treatment of the problem (section l). In section 2, I will try to locate Reichenbach's problem within a much more generai philosophical framework, essentially proposed by the American philosopher Wilfrid Sellars almost fifty years ago.I regard this second section as particularly important, and not only as a generai introduction to our topi c: contemporary philosophy ofphysics is affected by a dangerous ternptation ofexcessive specialization, and by an attitude that considers technicalities as ends in themselves. Qua philosophers, we ought to understand, as Sellars put it, "how things (in the widest possible sense ofthe word) hang together (in the widest possible sense ofthe word)" In section 3, I will then distinguish amongfive different senses of"conventional", and will then study their logical relationship vis àvis the problem of establishing in which ofthese senses the relation ofsimultaneity could be regarded as conventional.