Has the theory of rationality as ‘openness to criticism’ solved the problem of ‘rational belief in reason’? This is the main question the present article intends to address. I respond to this question by arguing that the justified true belief account of knowledge has prevented Karl Popper’s critical and William Bartley’s pan-critical rationalism from solving the problem of rational belief in reason. To elaborate this response, the article presents its arguments in three stages: First, it argues that the idea of (...) objective knowledge as justified true belief leads to the equation of objective knowledge with justification. Hence, if we base the theory of critical rationalism, as openness to criticism, upon such a conception of knowledge, our theory of rationality involves in infinite regress of proofs. Second, it argues that Popper describes critical rationalism as an ‘irrational attitude’ of openness to criticism because the rationalist cannot justify his belief in reason by argument or experience. Thus, since Popper assumes that ‘a belief in reason’ must be justified in order to be ‘rational’ he cannot lead to a solution for the problem of rational belief in reason. Third, it argues that, like Popper’s critical rationalism, Bartley’s pan-critical rationalism originates in the justified true belief account of knowledge, however, not because Bartley defines critical rationalism as irrational faith in reason, but because his theory does not tell us how an ‘open’ belief in reason is to be refuted logically. The reason for this failure is that Bartley uses Popper’s epistemology of science to define the conception of criticism. While Popper and Bartley are recognized as the non-justificationist philosophers of science and rationality, this article tries to reveal that the idea of objective knowledge as justified true belief has prevented them from showing how ‘a rational belief in reason’ can be defended by argument. The article also briefly shows the consequence of this study for a notable change in the logical foundations of science. (shrink)