Have you experienced that awkward situation in which, having just presented the good news of Jesus Christ, the man or woman on the other side the table says something like, “I see, I understand how much that truth means to you, but it is not for me”? In this situation the absolute truth claims of Jesus Christ–that He is the only way to the Father and the only true God–are met with pluralistic acceptance: Jesus is added to a virtual pantheon of spiritual gurus and self-help teachers. For many Postmoderns, those who hold the worldview of postmodernism, all “truths” are equally valid. When presented with the choice of Jesus or rebellion against God, they resort to pluralism–Jesus is good, but not Jesus alone–or skepticism–boy, that seems intolerant, how can you be so sure that you are right and everyone else is wrong? Both of these answers are really the same: they reason that there is truth in all religions and philosophies, so how can one religion or philosophy claim to be the only one; or that it is impossible apart from perfect knowledge–which none of us have–to know which one is right after all, are they not all probably perspectives on one reality? I have argued elsewhere that all rational thought requires a foundation only the Bible can provide; does irrationalism escape this need? I don’t believe it does: Postmodern irrationality presupposes the rationality of irrational reason, therefore it presupposes what only the Bible can provide and is, therefore, self-defeating.
Stay with me for moment here; this is not as complicated as it may sound. If by rationality I mean that human reason functions and is able to arrive at truth (logic works), then irrationality is the claim that human reason is unable to arrive at truth (logic does not work). Postmodernism is irrational because it claims that individual may have personal truth (it can be true for you) but not public truth (it can be true for you, but other contradictory truths are true for me; your truth has no greater resemblance to reality than mine), yet it argues for this irrationality with reason.
Think of a conversation such as the one above; how often does a skeptic make a claim that all religions are partially or wholly right and compatible, or that Jesus is good but not the only way, without argument? I have never read or experienced this: everyone tries to convince me that my intolerance is wrong. Appealing to the value or beauty of the Quran, they say: how can you deny that there is truth here? Implicitly, they reason: if truth is in the Quran and truth is in the Bible, both must be equally true. Or they say that the claim that Jesus is the only way is intolerant, reasoning in such a way as: because Jesus is the only way to heaven, all other supposed ways are false, therefore to claim that Jesus is the only way is to be intolerant. Further deducing that because intolerance is wrong, the claim that Jesus is the only way to heaven is wrong. There are so many problems with this reasoning, but let it suffice to point out one: all these claims for irrationalism presuppose rationality. That is, they presuppose that basic logical functions work and that they are shared between minds (why else would you use them to convince me?); they also presuppose that we both have access to standard of right or wrong (intolerance = wrong) by which we can measure thoughts and actions. As I have argued elsewhere, all of this–rationality and morality–require the Bible.
In brief, rationality requires knowledge from which to reason, the existence of objective rationality (logic works), and enough knowledge to be sure of the conclusion (on which, see here). Basically, to reason you need knowledge, known from birth or acquired from experience: if it is known from birth, its origins have to be explained by something outside of humanity; if it is known from experience, one needs a reason to trust experience. The only way we can trust our experience is if someone who knows all things and is trustworthy tells us our senses are trustworthy: we need the Bible. Innate knowledge requires a creator and empiricism requires special revelation, so the building blocks of rationality require the Bible and God who gave it. Objective rationality requires a mind that has always existed (where did logic exist if there was never a mind to think it?), and our assurance of its validity requires a higher authority confirming that our reasoning is indeed trustworthy–we need the Bible. Finally, we need knowledge of all reality to understand its parts, or in the absence of such complete knowledge, we need the insight of one who has it: again, we need the Bible. Therefore, the rationality implied in Postmodern irrationality needs God’s revelation in the Bible as much as Empiricism and Rationalism, and therefore contradicts itself: if rationality requires the objective revelation of the God in Scripture and irrationality presupposes rationality, irrationality is inconsistent and requires inconsistently that the Bible is true for all people. Postmodernism will, of course, deny both rationality and the Bible, and so will remain hopelessly inconsistent. (This of course leaves a lot unsaid, but good places to start for going further are John Frame’s Apologetics: a Justification of Christian Belief and The Doctrine of the Knowledge of God.)