ABSTRACT The status and role of Popper’s ‘Rationality Principle’ (RP) is still the subject of disputes. The ‘prevailing view’ among Popper’s commentators seems to be that RP is better interpreted as a methodological principle. Yet, this view is challenged in a recent study where RP is interpreted as an‘idealization’. We critically review these two accounts of RP and propose a novel one according to which RP is, first and foremost, the scientific version of a heuristic that ordinary people unconsciously use (...) when they seek to explain and predict other people’s behavior. However, we recognize that, to the extent RP is part of a methodological strategy whereby, in the wake of adverse empirical results, social scientists place the ‘onus of proof’ on their situational model it is legitimate to claim that RP is adopted, at least partly, for methodological reasons. Further, to the extent that the adoption of RP implies suppressing those mental processes that may affect actors’ reasoning and willpower it is also legitimate to claim that RP is, at least partly, an ‘idealization’. We conclude that the status and role of RP is multi-faceted and that the three accounts of RP complement each other. (shrink)