How did Immanuel Kant and Jeremy Bentham weaken confidence in natural law?

In the early 19th century, the influence of Immanuel Kant and Jeremy Bentham significantly eroded the prevailing confidence that "nature" could serve as a foundational source for moral or legal norms.1

Immanuel Kant

Kant’s contribution to this skepticism stemmed from his critical philosophy, which emphasized that morality must be grounded in the formal principles of reason rather than speculative metaphysics or empirical observations of nature. By establishing the categorical imperative—the requirement that one act only on maxims that can be willed as universal laws—Kant shifted the focus of ethics away from natural inclinations or "natural" states toward the autonomous, rational will of the individual.123

Jeremy Bentham

Bentham, a founder of utilitarianism, launched a more direct and aggressive assault on the doctrine of natural law. He famously dismissed the concept of natural rights as "rhetorical nonsense" and "nonsense upon stilts," arguing that rights are exclusively the creation of positive law. For Bentham, the legitimacy of laws and institutions should be tested solely by the principle of utility—their ability to maximize happiness and minimize pain—rather than by appeals to abstract or "imaginary" natural laws.145

Together, these thinkers fostered a climate of skepticism that replaced traditional natural law theories with frameworks centered on human reason, utility, and legislative sovereignty.14