The Mystery of Applied Mathematics?: A Case Study in Mathematical Development Involving the Fractional Derivative

I discuss the applicability of mathematics via a detailed case study involving a family of mathematical concepts known as 'fractional derivatives.' Certain formulations of the mystery of applied mathematics would lead one to believe that there ought to be a mystery about the applicability of fractional derivatives. I argue, however, that there is no clear mystery about their applicability. Thus, via this case study, I think that one can come to see more clearly why certain formulations of the mystery of applied mathematics are not convincing.