10.3 Does Natural Law Require a Belief in God? 

Aquinas himself devised his theory of natural law specifically to show how all human beings, regardless of upbringing or culture, can discern right and wrong based upon their innate reason given their nature as human beings. He wrote in a time when medieval Christianity was struggling to deal with non-Christian religious perspectives, especially those of Islam. Appeal to the Bible (Divine Command Theory) could no longer serve as a basis for moral conversations with other worldviews. And of course, there were agnostics and atheists even within the Christian world who would find arguments appealing to scripture meaningless. To be fair, Aquinas believed that these other points of view were often wrong. Yet to defend this, he needed to appeal to the innate natural law, arguing that because we are all human beings we can praise or condemn others for their moral actions accordingly.

There are also secular versions of natural law theory. These approaches argue that objective moral truths can be derived from rational examination of human nature and the world around us, without necessarily invoking a divine source. Immanuel Kant was in no way a Divine Command theorist but, as we have seen, did utilize the fundamental Natural Law contention that all of us are imbued with human reasoning from which we can derive absolute moral rules. Modern natural law thinkers like John Finnis have developed natural law theories that don’t rely on theistic premises, focusing instead on basic goods and practical rationality. Unlike classical natural law theorists, Finnis doesn’t rely on God or divine command as the source of natural law. He emphasizes how we can use reason to identify and pursue basic human goods. Instead, he relies on what he calls “practical reasonableness” to come up with certain core human “goods” (forming a coherent life plan, not arbitrarily preferring one good over another, not arbitrarily preferring one person over another, following one’s conscience, et. al.) which serves as the basis for moral reasoning. (Finnis, J. (1980). Natural Law and Natural Rights. Oxford University Press. This is Finnis’s seminal work where he lays out his theory of natural law.)

Contemporary secular Natural Law thinkers have adapted the classical theory to modern contexts, often without relying on theological premises. John Finnis, as we’ve seen, developed a secular version of Natural Law theory. In his Natural Law and Natural Rights he identifies seven basic goods: life, knowledge, play, aesthetic experience, sociability, practical reasonableness, and religion, arguing that these goods are self-evident and universally valuable. Robert P. George, although religiously affiliated, presents in his In Defense of Natural Law (2001) secular arguments for Natural Law focusing on applying Natural Law to bioethics, marriage, and sexuality. He advocates for a more conservative interpretation of Natural Law principles. Martha Nussbaum, a prolific contemporary writer in ethics, developed the “capabilities approach,” which has similarities to Natural Law theory in her Creating Capabilities: The Human Development Approach (2011). She identifies central human capabilities that should be protected and promoted in the global development and policy world. In the sphere of legal studies there is also a revived interest in Natural Law. In his The Morality of Law (The Storrs Lectures Series, 1969) Lon L. Fuller argues for the “inner morality of law,” suggesting that legal systems must adhere to certain principles to be considered valid. Michael S. Moore works on the application of Natural Law theory to criminal law and calls for a form of moral realism based on Natural Law principles in his Placing Blame: A General Theory of the Criminal Law (1998).

These modern thinkers share some common themes. First, they emphasize practical reason and argue that moral truths can be discovered through rational reflection on human nature and experience. In addition, they generally believe in the existence of objective moral principles, contrary to moral relativism. Most identify fundamental goods or capabilities essential to human flourishing. So too, they often critique pure consequentialism, arguing that some actions are inherently wrong regardless of outcomes. Furthermore, they typically place a strong emphasis on the inherent worth and dignity of human beings. Finally, they seek to spread the applications of natural law to new fields of inquiry. These thinkers often apply Natural Law principles to modern ethical dilemmas in fields like bioethics, environmental ethics, and political philosophy.

It’s worth noting that while these thinkers are considered “secular” in their approach, they often engage with religious Natural Law traditions, and some may have personal religious beliefs. Their arguments, however, are generally framed in terms accessible to secular discourse.