The QOTD, on the limits of reason:

“The third problem, that of conflict between knowledge and rationality… is often called the dilemma of ultimate commitment and the problem of presuppositions.

The problem is crucial, not only because no one has seemed able to solve it but because the Christian commitment of many Protestants depends upon the assumption that it cannot be solved. For the argument provides a rational excuse for irrational commitment… It argues that (1) for certain logical reasons, rationality is so limited that everyone must make a dogmatic irrational commitment; (2) therefore, the Christian has a right to make whatever commitment he pleases; and (3) therefore, no one has a right to criticize him (or anyone else) for making such a commitment…

No matter what belief is advanced, someone can always challenge it with: ‘How do you now?’, ‘Give me a reason’, or ‘Prove it!’ When such challenges are accepted by citing further reasons which entail those under challenge, these may be questioned in turn. And so on forever. If the burden of proof or rational justification is perpetually shifted to a higher-order premise or reason, the contention originally questioned is never effectively defended… An infinite regress is created.

To justify the original contention, one would eventually have to stop at something not open to question for which one does not and need not provide justificatory reasons. These would be the halting points for rational discussion… However, if all men do not cease their questioning at the same point - if ultimate standards are perceived not to be certain or if different people deem conflicting ‘ultimate’ standards to be certain - then ‘ultimate relativism’ results. Some way of arbitrating rationally among competing ultimate stopping points by appeal to a common standard is now excluded in principle. If these ultimate statements are matters of contention, then there will be no Archimedes’ lever with which to decide among competing sets of ultimate standards. Indeed, even if everyone did subjectively happen to stop at the same place or accept the same standard, there still would be no way to prove rationally that this universal subjective standard led to objectively true statements about the world…

Obviously, one cannot, without arguing in a circle, justify the rationality of a standard of rationality by appealing to that standard… The limits of rational argument within any particular way of life seem, then, to be defined by reference to that object or belief in respect to which commitment is made or imposed, in respect to which argument is brought to a close. Thus reason is relativized to one’s halting place or standards, and cannot arbitrate among different standards. Different halting places - i.e., standards, criteria, presuppositions, conventions, dogmas, articles of faith - are taken by different individuals and define irreconcilable communities. Whatever may explain how such differences arise, reason can never dissipate them.

– W.W. Bartley, III, The Retreat to Comitment, pg. 72-74.