Humans do two types of actions, polimorphic actions and mimeomorphic actions. The ability to carry out polimorphic actions cannot be mastered outside of socialization. Mimeomorphic actions, however, can be learned in other ways; sometimes, they can be learned away from the context of practice. Polimorphic actions cannot be mimicked by machines, but some mimeomorphic actions can. Other mimeomorphic actions are too complex to mechanize. Actions that cannot be mechanized because they are physically complicated should not be confused with actions that (...) cannot be mechanized because socialization is needed to master them. The analysis has implications for recent debates concerning the differences and similarities between humans and machines. The implica tion of the analysis is that much more can be understood about the relationship between humans and machines if the difference is treated as being a consequence of the unique properties of human societies. In this article, the analysis is applied to cardiac catheteriza tion, pacemaker implantation, simulation of bodies, and work in a medical "SkillsLab.". (shrink)