While there has been much discussion about the role of oaths in medical ethics, this discussion has previously centered on the content of various oaths. Little conceptual work has been done to clarify what an oath is, or to show how an oath differs from a promise or a code of ethics, or to explore what general role oath-taking by physicians might play in medical ethics. Oaths, like promises, are performative utterances. But oaths are generally characterized by their greater moral (...) weight compared with promises, their public character, their validation by transcendent appeal, the involvement of the personhood of the swearer, the prescription of consequences for failure to uphold their contents, the generality of the scope of their contents, the prolonged time frame of the commitment, the fact that their moral force remains binding in spite of failures on the part of those to whom the swearer makes the commitment, and the fact that interpersonal fidelity is the moral hallmark of the commitment of the swearer. Oaths are also distinct from codes. Codes are collections of specific moral rules. Codes are not performative utterances. They do not commit future intentions and do not involve the personhood of the one enjoined by the code. Recent attacks on oath-taking by physicians are discussed. Two arguments in favor of oath-taking are presented: one on the basis of the nature of medicine as a profession and the other on the basis of rule-utilitarian considerations. No attempt is made to define which oath a physician should swear. (shrink)