The Hippocratic Oath is an oath traditionally taken by physicians pertaining to the ethical practice of medicine. It is widely believed that the oath was written by Hippocrates, the father of medicine, in the 4th century BC, or by one of his students. It is thus usually included in the Hippocratic Corpus. Classical scholar Ludwig Edelstein proposed that the oath was written by Pythagoreans, a theory that has been questioned due to the lack of evidence for a school of Pythagorean medicine. Although mostly of historical and traditional value, the oath is considered a rite of passage for practitioners of medicine, although it is not obligatory and no longer taken up by all physicians.