The Hippocratic Oath is an oath historically taken by physicians, physician assistants' and other healthcare professionals swearing to practice medicine ethically. It is widely believed to have been written by Hippocrates, often regarded as the father of western medicine, or by one of his students. The oath is written in Ionic Greek (late 5th century BC), and is 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. Of historic and traditional value, the oath is considered a rite of passage for practitioners of medicine in many countries, although nowadays the modernized version of the text varies among them.