Enshrined in modern medicine is a distinct set of values. When medicine assumes these values uncritically, a host of ethical problems results. A glimpse at the ancient roots of modern medicine reveals that an older scientific tradition entertained a very different set of values--values that provide wise counsel and shed light on the specificf ethical concern of providing medically futile care to patients.
Hippocratic physicians in the fifth through third centuries B.C. were among the first to question the ethical limits of medicine. Historians regard one of their achievements to be an understanding of when and when not to intervene. In a work attributed to the Greek physician Hippocrates, it is written that the purpose of medicine is "to do away with the sufferings of the sick, to lessen the violence of their diseases," but also "to refuse to treat those who are overmastered by their diseases, realizing that in such cases medicine is powerless." According to this tradition, knowing the limits of medicine is related to the physician's appreciation of the art of medicine and the power of nature (physis). The predominant meaning of nature in the Hippocratic corpus is "the essential substances which make up human beings." The physician searched for the human being's natural state of health that had been altered by changes wrought by disease. The Hippocratic writings caution that should a physician demand "from an art power over what does not belong to the art, or from nature a power over what does not belong to nature, his ignorance is...allied to madness."  For the Greeks, medicine is techne, which implies doing. In doing, one is "bound...by the potentialities of the object...[and] by those of the techne itself."  According to this tradition, only the physician who understands natural limits and uses this understanding to set wise boundaries avoids the error of excessive confidence. The Greeks called this error hubris, and the tone of their approach counseled against it. In the words of one historian, "Those who disregarded the natural scope of therapies stained the authority of medicine." 
The basis for moderation and atttention to limits in Hippocratic medicine reflects the medical theories upon which Hippocratic medicine was built. Ancient medicine conceived its task to be one of working with human nature to assist in restoring disruptions in its natural order. Thus the author of the Precepts enjoined physicians to "display the discoveries of the art, preserving nature, not trying to alter it."  This viewpoint developed out of the Greek understanding of human health and disease. Health was viewed as a natural balance of four bodily humors (yellow bile, blood, black bile, and phlegm); disease was defined as an imbalance among these four. For example, a fever meant that too much yellow bile, and so too much heat and dryness, was present in the body. To restore health, a physician might instruct that water be used as a cooling agent: the patient might consume fluids or be immersed in cool water baths. Hippocratic physicians emphasized the importance of environment and climate in maintaining a natural balance within the body. Since human beings are under the influence of their essence or nature, in situations where disease is incurable the physician must accept that medical means should not be used.
The spirit of this approach is described by Plato, who extolled the kind of medicine taught by the followers of Asclepius. In the Republic, Plato emphasizes that
Asclepius...taught medicine for those who were healthy in their nature...but were suffering from a specific disease; he rid them of it...then ordered them to live as usual....For those, however, whose bodies were always in a state of inner sickness he did not attempt to prescribe a regimen, or...to make their life a prolonged misery...Medicine was not intended for them and they should not be treated, even if they were richer than Midas. …