What is Truth?

On the Rational Limits of Atheism

The Challenge of Reason

If you ask a room full of philosophers to name the strongest challenge to an atheistic worldview, you’ll usually hear familiar answers.

Some will point to the fine-tuning of the universe – the uncanny way the laws of physics appear delicately balanced for life. Others will raise the hard problem of consciousness: how subjective experience arises from mindless matter.

These are formidable challenges, but there is another, less heralded problem which might also keep the thoughtful atheist up at night, looking out into the existential void. It concerns not the cosmos out there, but the reliability of the reasoning apparatus within.

The problem is our confidence in human reason itself.

Evolution as a Shared Starting Point

To be clear from the outset: this argument does not deny evolution by natural selection. On the contrary, it takes evolution as a given. The question is not whether evolution happened, but what follows from it philosophically.

On a naturalistic picture, the human brain is a physical system shaped by millions of years of evolutionary history. Our cognitive faculties – our perception, memory, inference – exist because they contributed to survival and reproduction. The more profound question is whether this evolutionary story, by itself, explains why we should trust those faculties when they are used to discover truth about reality at the deepest level.

Minds Built for Survival

It would be a mistake to say that evolution has nothing to do with truth. In a stable, law-governed world, creatures that reliably misperceive their surroundings will not last long. Accurate beliefs about predators, food, terrain, and other agents are important to survival. In everyday, practical domains, survival and local truth-tracking usually align.

But this alignment has limits.

Natural selection does not select beliefs because they are true. It selects behaviours because they are adaptive. And many very different belief systems can produce the same survival-enhancing behaviour.

A creature might flee because it believes:

• “That really is a tiger”
• “That is a dangerous spirit”, or
• “Running now satisfies a powerful taboo”.

As long as it runs, it survives. From evolution’s point of view, these belief systems are interchangeable. This is the point emphasised by Alvin Plantinga in his Evolutionary Argument Against Naturalism. The issue is not that evolution produces useless minds, but that it does not guarantee truth-tracking belief as such.

Beyond the Evolutionary Pay-Off Zone

The problem sharpens when we leave the domains evolution directly shaped.

Our cognitive faculties evolved to handle mid-scale problems: navigating physical space, managing social relationships, anticipating threats. They work well in the environments for which they were selected. But the reasoning that leads to naturalism itself operates far beyond this evolutionary comfort zone. Questions about cosmology, metaphysics, probability, logic, and the ultimate structure of reality, had no obvious survival relevance. Yet it is precisely in these domains that we rely most heavily on abstract reasoning.

Here the evolutionary explanation grows thinner; not false, but incomplete.

Evolution may explain why we reason, but it does not explain why that reasoning should be trusted when it ranges far beyond survival-relevant tasks.

The Self-Undermining Loop

This is where there is a genuine epistemic tension for the naturalist.

1. We use our reasoning faculties to examine the evidence for evolution and naturalism.
2. We conclude that they are true.
3. But those same theories explain our reasoning faculties as tools shaped for survival, not for discovering abstract truth.
4. Which gives us reason to doubt their reliability in precisely the domains where naturalism is defended.

The issue is not that evolution makes reason unreliable across the board. Rather, it’s because it offers on its own no non-circular explanation for trusting reason at the level required to justify itself. That is the sense in which the circle threatens to become self-undermining.

The Theistic Contrast

Why does this tension seem to press more heavily on atheism than on theism? Because the theist has an additional explanatory resource. If a rational God exists and intends creatures to know the world, then the general reliability of human reason is not surprising. Our cognitive faculties may still be fallible and biased, but their truth-tracking capacity is not accidental. This is sometimes described as a virtuous circle rather than a vicious one: reason leads to God, and God explains why reason is broadly reliable.

The atheist, by contrast, must treat the reliability of reason as a fortunate by-product of evolutionary history – effective, but ultimately unguided.

An Unsettling Conclusion

What remains is a quiet explanatory gap.

In a universe without God, human reason appears as an extraordinarily useful biological adaptation, but one whose connection to truth, especially ultimate truth, is less secure than we usually assume.

This raises a haunting possibility: If naturalism is true, on what basis can we trust our very conception of truth and reason?

What is truth? It is the question that echoes down the ages and has never gone away. And it is a question that can keep more than just the thoughtful atheist wide awake at night.