Medical theory is specifically nosology - theory of illness or disease - especially etiology - theory of the cause of disease. Two competing theories dominate the tradition of medical theory: generalism — illness is disharmony, ill-balance — and externalism — illness is the intrusion of (hostile) foreign agents or factors — both theories represented, largely, by internal medicine and by surgery. The success of each theory is reinterpreted by the other — at times successfully. The bias of externalism is mechanistic, of generalism holistic. The scientific revolution was mechanistic, contemporary science holistic. Holism is clearly superior, yet it could not win (in physics and elsewhere) before the Einsteinian revolution in physics, since the success of mechanism could not be properly handled by holists until Einstein took the method of approximation to be the standard of scientific progress: a new theory must explain the success of its predecessor by presenting it as approximate. Each mechanistic (externalist) success, thus, should be presented as an approximate to a holistic (generalist) theory — indeed sets of mechanistic approximations for diverse holistic situations are called for. Hence, from a modern holistic viewpoint both generalism and externalism are viable and indispensable with.