Abstract: History and Philosophy of Science and Medicine in Japan Vol. 2: Oni, Yokai and Evil Spirits as Causes of Illness (日本医療科学の哲学と歴史　第２弾：病因としての鬼、妖怪、そして魔)

Having spoken of the scientific attitude in pre-modern Japan through the eyes of Ninja, who supposedly possessed supra human knowledge of the human behavior and natural medicine, it is now time to delve further into the Buddhist conception of how the world operated. In the first part of my research, I discussed the ways in which a particular group of war specialists in Japan developed their own system of scientific knowledge, prior to the Western contact, and thus making it distinctly Japanese. This group of war specialists, Ninja, studied extensively on human behavior and psychology but my studies have shown that they had poor understanding of medicine and lacked the interest as well as the philosophical rigor in discovering the causes of illness, which in turn led them to essentially rely on nothing but the placebo effect in curing sickness. Hence, in this second part of my research into the history and philosophy of science and medicine in pre-modern Japan, I will look at the broader perspective on medical theory and attitudes towards illness amongst the monastic doctors as well as the commoners prior to the importation of the Western science. In particular, my interest is in the etiology of various types of sickness and how people in Japan dealt with the symptoms. It is of course not possible to speak of purely Japanese practice, since Chinese influence is everywhere seen. However, my study will show that Japanese Buddhist philosophy nevertheless developed distinct features unique to Japan, perhaps as a result of the synthesis of the Buddhism with the Japanese native religion of Shintoism. It is in this context that I will be discussing about the medical philosophy proper to Japan, which must have existed in order to account for sickness and beliefs unique to the culture that were not found in the continent. In this article, I will focus on the supernatural yet real causes of illness according to the Shinto-Buddhist philosophy. Indeed, in the pre-modern period Japan, the causes of illness were explained in terms of the Traditional Chinese medical philosophy, Taoism, and Buddhist medical theory. According to one such view heralded by the etiology explained in the most widely studied book, Makashikan, written in the 6^th century by the founder of Tien Tai school, Chigi (538-597), the major causes of illness were six in number. They are 1) the imbalance of four elements, 2) excessive eating and drinking, 3) lifestyle related diseases, 4) daimon, 5) evil spirits, and 6) deeds in the previous life. Of these, the first three are natural causes and thereby can be treated with the medical knowledge. On the other hand, the latter three are supernatural causes and cannot be treated except spiritually, i.e. one must follow the path of the Buddha. I will focus in particular on the daimon and evil spirits in the field of medical thought in pre-modern Japan. I will unveil the familiar concepts of Oni and Yokai in light of medical context in the history of Japan, and analyze the ways in which these supernatural forces came into the medical philosophy in the Japanese monastic medicine. Taku Shinmura, Medical History in Japanese Buddhism, 34-36.