Despite denying the existence of justification and stressing our pervasive fallibility, critical rationalists are actually epistemological optimists. That is, we believe that progress is not only possible but actually the norm. While error is ubiquitous, most of our attempts to correct error are real improvements. While we may often just replace one mistaken hypothesis with another, successor hypotheses are generally better explanations, closer to the truth, and more useful than their predecessors. We can even learn to get better at identifying and correcting errors, and that is what critical rationalism is all about.
However, there is an argument that if our best efforts to correct error may themselves be erroneous, then it must be futile to even try. Criticism, in this view, is powerless unless it comes from an incorrigible source, a window on reality unsullied by subjective judgement. About this manifest truth, there can be no question or disagreement among sane men. To experience it is to be compelled. We cannot doubt or resist, and those who deny are either liars or lunatics. To say that all criticism is itself open to criticism is tantamount to saying that criticism is impossible.
Genuine progress, in this view, cannot be achieved by fallible methods. How, then, can critical rationalists embrace both fallibilism and epistemological progress at once?
For critical rationalists, progress is not measured by subjective confirmation or assurance. That kind of progress is indeed illusory. Though we may feel more or less confident in light of new evidence or arguments, it is always possible that we are most wrong about that which we believe most strongly. For critical rationalists, rather, progress takes a decidedly objective turn. The growth of knowledge is understood as a gradual process of trial and error, conjecture and refutation, or mutation and selection. Progress occurs when old problems are, in actual fact, solved and new problems discovered, when better explanations are found, or the truth better approximated. Whether people feel doubtful or confident, dogmatic or sceptical, is neither here nor there.
In this view, epistemological progress began even before there were subjective experiences and beliefs. There is a continuum between the parochial knowledge embodied in organic structures and the universal abstract products of human minds (science, philosophy, mathematics, etc.). In a sense, our genomes must first “know” how to create beings capable of having experiences and beliefs. This gradual evolution–this growth of knowledge–that made us possible required nothing like subjective assurance or confirmation to be successful.
Objectively, the enterprise of science and human rationality, critical discussion, conjecture and refutation can and, we conjecture, do work. If that is the standard of progress, then progress is indeed possible without the subjective assurance of a “manifest truth”. This is, in a nutshell, how critical rationalists can be both fallibilists and epistemological optimists.