In October 1789, a physician submitted a proposal to the French government for a new method of capital punishment: a decapitating machine. He thought this device would be more humane than other methods of execution, such as hanging. Nothing came of his proposal until December, when Dr. Joseph-Ignace Guillotin was able to present his idea in a speech before the National Assembly. In a moment of enthusiasm, he told his audience: “Now with my machine I take off your head in the twinkling of an eye, and you never feel it.” His words were met with mockery; his critics said it was ludicrous for a doctor of all people to endorse a mechanism for chopping off heads. A popular French journal even published a song ridiculing Guillotin. Within a decade, though, the guillotine had been used to execute the king and queen of France, revolutionary leaders, and common criminals. In lending his medical authority (and his name) to a method of execution—to a way of taking life rather than saving it—Guillotin was in some sense ahead of his time. The nineteenth and twentieth centuries would furnish more examples of doctors as agents of death.

In his new book titled Hippocrates’ Oath and Asclepius’ Snake: The Birth of the Medical Profession, philosophy professor T. A. Cavanaugh argues that the medical profession has its own unique set of ethics founded on the Hippocratic Oath, which prohibits a doctor from deliberately inflicting harm. But today, the author argues, many physicians have strayed from their original professional ethics by participating in assisted suicide, capital punishment, and abortion. In order to maintain the integrity of the profession, medicine should reconnect with the principles that served as its ethical foundation for centuries.

At the beginning of his book, Cavanaugh states that the Hippocratic Oath “establishes boundaries within which ethical medicine takes place.” Relying on his knowledge of ancient Greek mythology and culture, Cavanaugh makes an intricate argument to show that medicine’s most important characteristic is that it is a profession “devoted wholly to therapy, explicitly excluding deliberate wounding.” Physicians, therefore, should never intentionally take a life under any circumstances.

To make his point, Cavanaugh delves deeply into the oath and its relationship between healing and wounding. He begins by discussing snakes and their association with medicine. Snakes appear on ambulances and pharmacy doors, and in the insignia of the American Medical Association and the World Health Organization. Why does medicine, a profession associated with healing, use a creature most people find terrifying as its symbol? The answer might surprise you. While some snakes have the ability to kill with their venom, they also undergo an amazing type of molting called ecdysis, whereby they regularly shed their entire outer skin in one piece. This made the snake a symbol of rejuvenation—and, by extension, of healing.

This is why doctors have used Asclepius’s rod, entwined with a snake, as a symbol of their profession. Asclepius, the Greek demigod of medicine, is portrayed in Homer’s Iliad as the “blameless physician” who uses a staff, or walking stick, as he travels from town to town to treat patients. The snake wrapped around his staff reminds us that doctors are powerful—they have enough knowledge of human anatomy, biology, and drugs to heal us, or to kill us. It is for this very reason, Cavanaugh argues, that the Hippocratic Oath came into existence. (Whether or not the historical Hippocrates actually wrote the oath that bears his name is open for debate. Cavanaugh makes the case that he did.)

Because of a doctor’s ability to kill or to heal, one of the oath’s original purposes was “to eradicate deliberate wounding from the healer’s role” by means of a public promise. In his detailed examination of the Hippocratic Oath in its original Greek, Cavanaugh explains that the physician promises several things, among them that the oath-taker will act to benefit the sick and protect them from “harm and injustice.” At the end of the Oath, certain acts are specifically singled out as examples of what is harmful and unjust. These include the administration or recommendation of a deadly drug or an abortive pessary to a patient.

Cavanaugh’s claim that medicine is solely a therapeutic profession is fundamental to his argument that a doctor should never, under any circumstance, assist in the killing of a patient.  “Medicine’s essential activity,” he writes, “does not concern ending sickness, but, caring for patients who labor under disease. Simply put, one cannot care for another by destroying that other, even at his request…. therapy, caring for a subject, requires that subject to exist so that he may receive one’s care.” Killing can never be therapeutic because it not only destroys the sick but undermines the trust needed between the doctor and the vulnerable patient. Assisting in a patient’s death also promotes the dangerous misconception that “killing solves human trials and tribulations.”

Why write a book about an ancient oath that is rarely used today? Because, Cavanaugh argues, oaths matter, even in our contemporary world. The practice of making public promises is an essential tradition that continues to mark our most serious commitments. Marriages, ordinations, judicial and political inductions—all these ceremonies include a public promise. These public declarations are important, Cavanaugh explains, because certain commitments involve unique ethical issues: in the case of marriage, fidelity; in that of elected office, serving the public good. Public promises expressly set boundaries limiting the promise-maker’s behavior. They also help hold people accountable for their actions.

In the medical profession, the author explains, an oath is critical for several reasons. Without a declaration doctors lose their ability to define their own profession and decide what is allowed and what is forbidden. A public promise also allows physicians to protect their profession from being manipulated for extrinsic purposes at odds with its essential activity, caring for the sick.

Yet today, the Hippocratic Oath is largely ignored in medical schools. In fact, there is no single pledge, no universal promise to protect patients from “harm and injustice.” Rather, medical students take a diverse variety of oaths. Some schools even allow students to write their own. This is problematic, Cavanaugh contends, because it shows that medicine no longer has a consensus about its own boundaries. “Absent such a declaration,” he writes, “physicians jeopardize their ability to determine what is and what is not medicine, and thereby, what they will and will not do.”

This is not a book for everyone. Cavanaugh’s detailed references to Greek mythology and classical Greek philosophy will be appreciated most by readers who have a keen interest in the history of medicine as well as an enthusiasm for ancient Greek history and culture. Still, there are some treasures here. Cavanaugh has recovered the root of medical ethics—the ancient recognition that medical skills can be used either to heal or to harm. Whether or not medicine’s unique ethical origins can be incorporated into today’s medical profession, as Cavanaugh hopes, is questionable. With increasing demand by patients to manage their own health care—and even their own deaths—the lines between what physicians should and should not do are increasingly blurry.