Taking up space: The case of the ether

Abstract This paper obtains some methodological lessons in theory construction and modification (generally called ‘theory choice’) using the ether as a test case. It focusses on this posit both because it has a long history but also because it is associated with some spectacular theories and theorists. In view of the fact that the ether has been expunged from contemporary science, the paper asks why it survived as long as it did, whether its discussion was a waste of space and where to go from here. The last of these questions concerns not just the ether but also similar posits currently in circulation or those that will enter circulation in years to come.