What is the 'Hippocratic oath,' and who was Hippocrates?

A white marble statue of Hippocrates standing at the top of a set of marble stairs near some trees and bushes
A statue of the physician Hippocrates stands in the city where he died: Larissa, Greece. (Image credit: Yoeml via Getty Images)

The Hippocratic oath is a pledge historically recited by physicians, who in reading the text, agree to uphold a specific code of medical ethics. Despite the original oath being written about 2,500 years ago, in the 5th century B.C., modernized versions of the pledge are still recited by doctors today. 

The original text of the oath is attributed to Hippocrates of Kos, a Greek physician and teacher often referred to as the "father of medicine."

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Who was Hippocrates?

Hippocrates of Kos was a Greek physician who lived from about 460 B.C. to 375 B.C., according to the Reynolds-Finley Historical Library (opens in new tab). At a time when most people attributed sickness to superstition and the wrath of the gods, Hippocrates taught that all forms of illness had a natural cause. He revolutionized medicine in ancient Greece by establishing its first known intellectual school devoted to teaching the practice of medicine. For this, he is widely known as the "father of medicine."

Approximately 60 medical documents associated with Hippocrates' name, including the famous Hippocratic oath, have survived to this day. These documents were eventually gathered into a collection known as the Hippocratic Corpus. While Hippocrates may not have written all of these texts himself, the papers are held to be a reflection of his philosophies. 

Through Hippocrates' example, medical practice was pointed in a new direction, one that would move toward a more rational and scientific approach to understanding and treating disease.

What are the 'four humors'?

Hippocrates is often credited with developing the theory of the "four humors," or fluids. The philosophers Aristotle and Galen also contributed to the concept. Centuries later, William Shakespeare incorporated the humors into his writings when describing human qualities.

The so-called humors were yellow bile, black bile, blood and phlegm, according to "The World of Shakespeare's Humors (opens in new tab)," an exhibition by the National Institutes of Health (NIH). Each humor was associated with a particular element (earth, water, air or fire); two "qualities" (cold, hot, moist, dry); certain body organs; and certain ages (childhood, adolescence, maturity, old age).

The theory of the four humors posits that interactions among the humors, qualities, organs and ages — as well as the influence of the seasons and planets — determined a person's physical and mental health, as well as their disposition or personality. 

(Galen used the term "temperament" to indicate that one's health and personality were literally affected by temperature — cold, hot, dry or wet. This notion is reflected in the idioms "catching a cold" or having a "dry sense of humor.") 

According to the theory of the four humors:

  • Yellow bile is related to the choleric disposition and the qualities of hot and dry. It is associated with fire, summer, the gallbladder and childhood. 
  • Black bile is related to the melancholic disposition and the qualities of cold and dry. It is associated with earth, winter, the spleen and old age.
  • Blood is connected to the sanguine disposition and the qualities of hot and moist. It is linked to air, spring, the heart and adolescence. 
  • Phlegm is related to the phlegmatic disposition and the qualities of cold and moist. It is connected to water, the brain and maturity. 

Differences due to age, gender, emotions and disposition could be attributed to the interactions of the humors, according to the NIH exhibition. Heat stimulated action; cold depressed it. Someone with a choleric disposition was courageous, but phlegm caused cowardice. Youth was hot and moist; age was cold and dry.

According to the ancient theory, the key to good health was to keep the humors in balance; an excess or deficiency in one or more of the humors was associated with disease. Food was one of the most important ways to help balance the ratio of these humors. In fact, one of Hippocrates' most famous quotes is, "Let food be thy medicine and medicine be thy food." 

Sometimes the doctor would let blood (open a vein and drain the patient's blood) or prescribe emetics (medicine that causes vomiting) in order to balance the humors, according to Liam A. Faulkner (opens in new tab), author of "Ancient Medicine: Sickness and Health in Greece and Rome (opens in new tab)," in a column for the series History in an Hour (opens in new tab).

Although these practices and the concept of the four humors may sound strange and unscientific today, these ideas represented the first step away from the predominantly supernatural view of sickness and a step toward a new idea that illness is related to the environment and what is going on inside the body.

What is the Hippocratic Corpus?

a marble relief that depicts either Asclepius or Hippocrates treating an ill woman while a number on onlookers stand nearby

This marble relief shows Hippocrates (or potentially Asclepius, the god of medicine) treating a sick woman. (Image credit: DEA / G. DAGLI ORTI / Contributor via Getty Images)

The Hippocratic Corpus, which is widely considered the oldest set of medical documents, is a collection of about 60 texts, or "books," containing lectures, textbooks, research, cases and philosophical essays on a variety of medicine-related subjects. 

Some of the writings are short, like only a paragraph, while others run several volumes, according to Faulkner. The styles differ widely throughout the collection, supporting the idea that it had several authors. Historians think the texts may be the work of numerous physicians practicing medicine during Hippocrates' lifetime and later, according to Biography.com (opens in new tab).

The corpus was ultimately assembled in Alexandria, Egypt, during the third century B.C. and eventually became the standard reference for up-and-coming physicians throughout the Western world, according to Faulkner. Many of the teachings were used well into the 19th century.

What is the Hippocratic oath and what does it say?

Often included in the Hippocratic Corpus is the Hippocratic oath, an ancient code of ethics for doctors. Although the oath is widely attributed to Hippocrates, it is still unknown whether he actually wrote it. Today, the oath is valued as more of a historic example of medical ethics and principles rather than one to be taken completely literally. 

Among the anachronisms in the original oath, physicians swear by the Greek gods and goddesses of health to follow the covenant to the best of their ability. According to a 2016 article published in The BMJ (opens in new tab), this pledge to the healing gods read as follows: "I swear by Apollo the Healer, by Asclepius, by Hygieia, by Panacea, and by all the gods and goddesses, making them my witnesses, that I will carry out, according to my ability and judgment, this oath and this indenture." 

The oath goes on to list some seemingly odd rules for doctors that would be quite difficult to apply in our current day and age. For example, it calls for free tuition for students of medicine, urges physicians to never use the "knife" (surgery) and suggests that they treat their teacher like a parent — in other words, to regard his children as brothers and to give him money if needed. 

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Contrary to popular belief, the words "first, do no harm" don't appear in the original Hippocratic oath, Dr. Robert H. Shmerling (opens in new tab), former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center and current corresponding faculty member at Harvard Medical School, wrote in a 2020 blog (opens in new tab) for the university. 

This phrase is actually drawn from a different text attributed to Hippocrates, called "Of the Epidemics." The exact origin of the phrase may have been muddled by the fact that several sentences with similar meanings appear in both texts, Shmerling wrote.

Do doctors still say the Hippocratic oath?

Today, many medical school graduates still recite modern variations of the oath, according to Peter Tyson (opens in new tab), author of a column for NOVA titled "The Hippocratic Oath Today (opens in new tab)." The following is a modern version of the oath written in 1964 by Dr. Louis Lasagna, then a professor of medicine at Johns Hopkins University and later dean of the Sackler School of Graduate Biomedical Sciences at Tufts University:

I swear to fulfill, to the best of my ability and judgment, this covenant:

I will respect the hard-won scientific gains of those physicians in whose steps I walk, and gladly share such knowledge as is mine with those who are to follow. I will apply, for the benefit of the sick, all measures [that] are required, avoiding those twin traps of overtreatment and therapeutic nihilism. I will remember that there is art to medicine as well as science, and that warmth, sympathy, and understanding may outweigh the surgeon's knife or the chemist's drug. I will not be ashamed to say "I know not," nor will I fail to call in my colleagues when the skills of another are needed for a patient's recovery. I will respect the privacy of my patients, for their problems are not disclosed to me that the world may know. Most especially must I tread with care in matters of life and death. If it is given me to save a life, all thanks. But it may also be within my power to take a life; this awesome responsibility must be faced with great humbleness and awareness of my own frailty. Above all, I must not play at God. I will remember that I do not treat a fever chart, a cancerous growth, but a sick human being, whose illness may affect the person's family and economic stability. My responsibility includes these related problems, if I am to care adequately for the sick. I will prevent disease whenever I can, for prevention is preferable to cure. I will remember that I remain a member of society, with special obligations to all my fellow human beings, those sound of mind and body as well as the infirm. If I do not violate this oath, may I enjoy life and art, respected while I live and remembered with affection thereafter. May I always act so as to preserve the finest traditions of my calling and may I long experience the joy of healing those who seek my help.

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According to the 2016 BMJ article, some doctors view saying the oath as a solemn rite of passage, while others can't even recall whether they've taken it. Some find that some of the oath's original text — such as "I will respect secrets confided in me" — still offers sound advice for modern medical practitioners, while others find much of the pledge irrelevant. 

To that end, some physicians believe the oath is simply inadequate to address today's economic, political and social challenges — for example, physician-assisted suicide and other practices that were unheard of in Hippocrates' time, according to Tyson. However, doctors still hold sacred its principles: treat the sick to the best of one's ability, keep them from harm and injustice, preserve patient privacy and teach the secrets of medicine to the next generation.

Traci Pedersen
Live Science Contributor
Traci Pedersen is a freelance author who has written extensively on themes of science, psychology, religion and alternative health for a variety of publications. She has also written 14 science chapter books and numerous teacher resource books for the elementary classroom. She is constantly brainstorming how to turn age-old topics into new and exciting stories.
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