Elucidating a metaphysics of medicine is vital for framing a coherent medical ethics. In this paper, I examine the historical case of Avicenna, the eleventh century physician-philosopher. Avicenna radicalizes the dissective power of reason using a logicized Aristotelian metaphysics to clarify concepts at the metaphysical level, which I call his anatomy of being. One of the practical consequences of Avicenna’s metaphysics is a dehumanizing eschatology of death. I outline the main elements of Avicenna’s thought that constitute his anatomy of being. (...) Through an examination of his logic, metaphysics, and psychology, I show how Avicenna develops a dissective logic. I conclude that one’s epistemology, as a method of knowing, entails a metaphysics, and, in turn, results in an ethical stance to the object of knowledge. For Avicenna, mental dissective logic applied to humans results in dehumanization, thereby destroying the humanistic impulse of medicine. (shrink)