 To this, Stathis Psillos (1999, Ch. 4) has responded by invoking a distinction credited to Richard Braithwaite, to wit, the distinction between premise-circularity and rule-circularity. An argument is premise-circular if its conclusion is amongst its premises. A rule-circular argument, by contrast, is an argument of which the conclusion asserts something about an inferential rule that is used in the very same argument. As Psillos urges, Boyd’s argument is rule-circular, but not premise-circular, and rule-circular arguments, Psillos contends, need not be viciously circular (even though a premise-circular argument is always viciously circular). To be more precise, in his view, an argument for the reliability of a given rule R that essentially relies on R as an inferential principle is not vicious, provided that the use of R does not guarantee a positive conclusion about R’s reliability. Psillos claims that in Boyd’s argument, this proviso is met. For while Boyd concludes that the background theories on which scientific methodology relies are approximately true on the basis of an abductive step, the use of abduction itself does not guarantee the truth of his conclusion. After all, granting the use of abduction does nothing to ensure that the best explanation of the success of scientific methodology is the approximate truth of the relevant background theories. Thus, Psillos concludes, Boyd’s argument still stands.