The standards of achievement within any craft are justified historically. They have emerged from the criticism of their predecessors and they are justified because and insofar as they have remedied the defects and transcended the limitations of those predecessors as guides to excellent achievement within that particular craft. Every craft is informed by some conception of a finally perfected work which serves as the shared telos of that craft. And what are actually produced as the best judgments or actions or objects so far are judged so because they stand in some determinate relationship to that telos, which furnishes them with their final cause. So it is within forms of intellectual enquiry, whether theoretical or practical, which issue at any particular stage in their history in types of judgment and activity which are rationally justified as the best so far, in the light of those formulations of the relevant standards of achievement which are rationally justified as the best so far. And this is no less true when the telos of such an enquiry is a conception of a perfected science or hierarchy of such sciences, in which theoretical or practical truths are deductively ordered by derivation from first principles. Those successive partial and imperfect versions of the science or sciences, which are elaborated at different stages in the history of the craft, provide frameworks within which claimants to truth succeed to fail by finding or failing to find a place in those deductive schemes. But the overall schemes themselves are justified by their ability to do better than any rival competitor so far, both in organizing the experience of those who have up to this point made the craft what it is and in supplying correction and improvement where some need for these has been identified.
– Alasdair MacIntyre, 1990