This episode takes a bit of a sidestep: instead of actual chemistry, we discuss the philosophy of chemistry, which underwent a revival in the 1980s and 1990s. We talk about the "ultimate units" of chemistry, what exactly does chemistry study, how chemistry is different from other sciences, what is a chemical bond, and what is a reaction mechanism. All of these topics are argued about by chemical philosophers--even as chemists go blithely on, doing whatever it is chemists do.