Many methodologists are firmly convinced that Popper's arguments concerning the status of the rationality principle (RP) are incoherent or incompatible with the essentials of falsificationism. The present essay first shows that the accusation of incompatibility of situational logic with falsificationism does not hold up to scrutiny but then shows that Popper's arguments are nonetheless flimsy if not indefensible. For it seems that one can distinguish between two different versions of the RP in Popper's writings. If the first version is plainly (...) "objectivist" and can be characterized with Popper as empirically false, the second one is rather "subjectivist" and is not falsifiable as such. The essay shows that this second reading of the RP is the one that Popper finally adopts but that, unfortunately enough, this formulation of the RP looks more like a metaphysical statement than like an empirical law. It could then be held to be a priori valid as such, by analogy with Popper's line of argument concerning the principle of causality. If this is correct, then Popper's thesis on the empirical status of the RP is confuted. (shrink)