The moral realism argument for God's existence claims that the objective reality of moral facts requires a divine foundation. The argument proceeds through three key premises: (1) objective moral facts exist independently of human beliefs or preferences; (2) such mind-independent moral facts require metaphysical grounding in a necessary being; (3) only God can provide the requisite ontological foundation for objective moral reality. Unlike arguments focusing on moral epistemology or motivation, this formulation specifically addresses the metaphysical status of moral properties themselves, arguing that their objective existence points to divine reality as the ultimate truthmaker for moral facts.
The argument's philosophical lineage extends from Plato's Form of the Good through medieval Islamic and Christian thought to contemporary moral philosophy. Al-Māturīdī (d. 944) developed early versions in his Kitāb al-Tawḥīd, arguing that objective moral properties require grounding in divine attributes. Thomas Aquinas articulated similar ideas in Summa Theologiae (I-II, q. 91), connecting eternal law to divine reason. Modern defenders include Robert Adams in Finite and Infinite Goods (1999), developing a theistic framework for moral realism, William Lane Craig in Reasonable Faith (2008), and David Baggett and Jerry Walls in Good God (2011). Contemporary philosophers like Mark Linville in "The Moral Argument" (2009) and C. Stephen Evans in God and Moral Obligation (2013) have refined the argument using recent work in metaethics.
Critics raise several objections to the moral realism argument. Erik Wielenberg in Robust Ethics (2014) defends non-theistic moral realism, arguing that moral facts can be brute features of reality requiring no further grounding. Michael Huemer in Ethical Intuitionism (2005) contends that moral properties might be sui generis, neither requiring divine nor naturalistic foundations. The Euthyphro dilemma challenges whether God grounds morality or merely recognizes it. Defenders respond that God's nature itself constitutes the Good, dissolving the dilemma. They argue that brute moral facts violate principles of sufficient reason, and that theism better explains the curious alignment between moral truth and human flourishing. William Alston in "What Euthyphro Should Have Said" (2002) and others maintain that divine nature theory successfully navigates between arbitrariness and independence.
The moral realism argument differs from related formulations in the moral argument family through its specific metaphysical focus. While the Kantian moral argument emphasizes practical reason and moral obligation, the moral realism argument addresses the ontological status of moral facts. Unlike divine command theory, which grounds morality in God's will or commands, this argument locates it in God's nature or being. The moral knowledge argument focuses on how we can know moral truths, whereas the moral realism argument asks what makes them true. The axiological argument encompasses all values including aesthetic ones, while this formulation specifically targets moral facts and their metaphysical requirements.