William Warren Bartley compared critical rationalism to the very general philosophical approach to knowledge which he called "justificationism". Most justificationists do not know that they are justificationists. Justificationism is what Popper called a "subjectivist" view of truth, in which the question of whether some statement is true, is confused with the question of whether it can be justified (established, proven, verified, warranted, made well-founded, made reliable, grounded, supported, legitimated, based on evidence) in some way.
According to Bartley, some justificationists are positive about this mistake. They are naïve rationalists, and thinking that their knowledge can indeed be founded, in principle, it may be deemed certain to some degree, and rational.
Other justificationists are negative about these mistakes. They are epistemological relativists, and think (rightly, according to the critical rationalist) that you cannot find knowledge, that there is no source of epistemological absolutism. But they conclude (wrongly, according to the critical rationalist) that there is therefore no rationality, and no objective distinction to be made between the true and the false.
By dissolving justificationism itself, the critical rationalist regards knowledge and rationality, reason and science, as neither foundational nor infallible, but nevertheless does not think we must therefore all be relativists. Knowledge and truth still exist, just not in the way we thought.
Read more about this topic: Critical Rationalism