Kant and Butler have a sharp methodological conflict in justifying moral obligations. While Kant argues that moral obligations can only be grounded in a prior justifications rather than in anything empirical, Joseph Butler grounds moral obligations in the empirical knowledge of human beings. Despite the apparent radical difference, I argue that Kant agrees with Butler that moral obligations must be grounded in the understanding of human beings. They, however, fundamentally disagree about human nature, which generates their methodological conflict in studying morality. For Kant, the essential attribute for human beings is autonomy, which presupposes independence from any particular experience. In contrast, Butler understands human nature as a system that includes different particular experience. Although there is no conclusive answer of the correct understanding of human nature, I suggest that Butler’s account of moral obligations is a plausible one that can be considered as a counterexample to Kant’s account.