  The natural response—and the response most frequentists  offered, with the possible exception of von  Mises[14]—was  to narrow  the available reference classes. (As noted in Supplement  A.3,  many frequentists were explicit that chances were frequencies in repetitions of natural kinds of processes.) Salmon (1977) appeals to objectively homogenous reference classes (those which cannot be partitioned by any relevant property into subclasses which differ in attribute frequency to the original reference class). Salmon’s proposal, in effect, is that homogeneous reference classes are random sequences, the evident circularity of which will hardly constitute a reply to the present objection. Reichenbach (1949: 374) proposed to ‘proceed by considering the narrowest class for which reliable statistics can be compiled’, which isn’t circular, but which fails to respond to the objection since it provides no guarantee that there will be only one such class. There may well be multiple classes which are equally ‘narrow’ and for which reliable statistics can be collected (Gillies, 2000: 816). In the present context, this will amount to a number of sequences long enough to make for reliable judgements of their randomness or lack thereof.