 Imre Lakatos (1970), who was for most of his philosophical career a follower of Popper, offers a broadly Popperian solution to this problem. Lakatos insists that testing is always comparative. When theories face empirical difficulties, as they always do, one attempts to modify them. Scientifically acceptable (in Lakatos’ terminology “theoretically progressive”) modifications must always have some additional testable implications; otherwise they are purely ad hoc. If some of the new predictions are confirmed, then the modification is “empirically progressive,” and one has reason to reject the unmodified theory and to employ the new theory, regardless of how unsuccessful in general either theory may be. Though progress may be hard to come by, Lakatos’ views do not have the same destructive implications as Popper’s. Lakatos appears to solve the problem of how to appraise mainstream economic theory by arguing that what matters is empirical progress or retrogression rather than empirical success or failure. Lakatos’ views have thus been more attractive to economic methodologists than Popper’s.