Popper's "rationality principle" reconsidered

Popper recognizes that there are, at least, two versions of his "Rationality Principle" (RP) yet he does not explain either how they relate to other parts of his works or which version social scientists should adopt. We argue that Popper's formulation of RP can be upgraded by explicitly considering the conjectural nature of all knowledge and the subjective nature of the "facts" of the social sciences. Next, we examine several areas of Popper's work as well as some of Hayek's ideas and conclude that, had Popper reflected on these issues he would probably recommended social scientists to adopt the ‘subjectivist’ version of RP.