In this thought-provoking revised edition, Professor J. Budziszewski boldly challenges the prevailing notion that moral truths are beyond human comprehension. Through lucid and logical reasoning, he revives the natural law tradition, reinvigorating faith in a moral code rooted in human nature. What We Can't Not Know masterfully exposes the rational underpinnings of our innate sense of right and wrong, and reveals how this foundation has been eroded in Western society. Having personally navigated the depths of atheism and nihilism in his own quest for truth, Budziszewski intimately understands the philosophical and personal undercurrents driving moral relativism. With the wisdom of experience and rigorous intellectual inquiry, he offers a sturdy anchor to those seeking to grasp or defend traditional morality. By bridging the divides between religious and philosophical perspectives, natural law theory enters a new era, where theology assumes a vital role. Rather than hindering the pursuit of common ground, religious belief becomes a gateway to universal norms of behavior. Budziszewski compellingly argues that natural law is not a rival to theology, but its most faithful exponent. The book culminates in a searing critique of modernity, which has lost sight of the fact that human beings are not isolated individuals, but integral parts of a broader human community, and that true fulfillment lies not in self-assertion, but in self-sacrifice.