 Lakatos’s last publication was an historical a case-study, co-authored with Elie Zahar and published after his death. It argues that the methodology of scientific research programmes can explain the Copernican Revolution as a rational process by which an earlier theory (Ptolemy’s geocentric theory of the Cosmos) was dethroned in favour another objectively better one (Copernicus’s heliocentric theory). It thus demonstrates the rationality of the Copernican Revolution (one of the most dramatic episodes in the history of thought) and confirms the MSRP as a theory of scientific rationality (so long as we accept the inductive principle that the more “great science” that a demarcation criterion can represent as rational, the more likely it is to be correct).