Gradualism, Vagueness, and Moral Agency: A Critique of Korsgaard’s Saltatory Change Hypothesis

This paper defends an evolutionary gradualist account of moral agency against Christine M. Korsgaard’s saltatory moral evolution hypothesis. Korsgaard, drawing on Kantian notions of normative self-government, posits that moral agency emerged fully formed at a singular point, a unique capacity that decisively separated humans from our non-moral animal ancestors. I challenge this claim by invoking the Sorites paradox and a novel “Killing Case” paradox (KCP), highlighting the problem of vagueness inherent in drawing any precise boundary within a continuous evolutionary process. Specifically, KCP shows that any attempt to identify a precise boundary within a continuous evolutionary process inevitably leads to logical contradictions or self-defeating conclusions, thus providing a novel logical tool beyond the traditional Sorites paradox. Korsgaard’s model effectively demands identification of an exact threshold for the onset of moral agency, which leads to logical contradictions and epistemic indeterminacy. Furthermore, I marshal empirical evidence from evolutionary biology, primatology, and moral psychology indicates that complex social behaviours such as empathy, fairness, and norm-sensitivity appear in nonhuman animals to varying degrees. These behaviours serve as transitional forms and provide no evidence for any sudden or singular biologically unexplained cognitive mutation. I also consider potential counterarguments, such as proposals of specific cognitive thresholds or binary divisions in moral status and find them unpersuasive. I conclude that a gradualist model of moral evolution is both philosophically more coherent and empirically better supported. Human moral agency likely arose through numerous small evolutionary steps rather than a single leap, preserving continuity while accounting for human normativity.