Scientific Rationality: Phlogiston as a Case Study

I argue that it was rational for chemists to eliminate phlogiston, but that it also would have been rational for them to retain it. I do so on the grounds that a number of prominent phlogiston theorists identified phlogiston with hydrogen in the late 18th century, and this identification became fairly well entrenched by the early 19th century. In light of this identification, I critically evaluate Hasok Chang's argument that chemists should have retained phlogiston, and that doing so would have benefited science. I argue that these benefits would have been unlikely, and I go on to consider some more likely benefits and harms of retaining phlogiston. I conclude that there is a sense in which scientific rationality concerns what is permissible, as opposed to what is required, so that retention and elimination may, at least sometimes, both be rationally permissible options.