Biomedical ethicists often assume that common morality constitutes a largely consistent normative system. This premise is not taken for granted in general normative ethics. This paper entertains the possibility of inconsistency within common morality and explores methodological implications. Assuming common morality to be inconsistent casts new light on the debate between principlists and descriptivists. One can view the two approaches as complementary attempts to evade or transcend that inconsistency. If common morality proves to be inconsistent, then principlists might have reason to prefer a less pluralist theory, thereby moving closer to descriptivism. Descriptivists, by contrast, might want to qualify their claim to accommodate all of people's basic moral convictions. Finally, both camps might wish to adopt a more revisionist posture, accepting that an adequate ethical theory occasionally will contradict some of people's deepest moral convictions. Proper application of the method of reflective equilibrium, to which both descriptivists and principlists claim allegiance, may entail greater openness to revisionism than either camp admits.