 For Popper, a conjecture is ad hoc “if it is introduced…to explain a particular difficulty, but…cannot be tested independently” (Popper 1974: 986). Thus Popper’s conception of ad hocness added to the ordinary English meaning a further requirement—in the case of an ad hoc hypothesis that was simply introduced to explain a single phenomenon, the ad hoc hypothesis has no testable consequences other than that phenomenon. In the case of an ad hoc theory modification introduced to resolve an anomaly for a theory, the modified theory had no testable consequences other than those of the original theory. 