Since the isolation of embryonic stem cells from humans, the words stem cell havebecome the focus of intense debate. The concern is with the nature of stem cells: are they themedical miracle that will cure diseases like Alzheimers disease, type-I diabetes and Parkinsonsdisease, or are they the murder of an innocent developing form of life? Attempts to answer thesequestions raise issues of definition namelare stem ceylls?, wh This disseat rtation examinesthe strategies of definition used in the political and scientific debates from December 1998 toApril 2002, a period that covers the major political and scientific milestones in the early debateover embryonic stem cells. Definition is understood as the creation of a quasi-stable point fromwhich individuals launch arguments. Those quasi-stable points are created through theorganization of a series of fragments. Three strategies play a role in the development of thepolitical and scientific definitions of stem cell and embryonic stem cell. First, rhetors appeal tofuture applications as a justification for research: in this way, stem cells become defined by theirpurpose, the potential applications that they can be used to realize. Scientists offer a list of threepotential applications, which political rhetors reduce to one direct medical application. Thisshift in application changes how stem cells are defined. Second, both scientific and politicalrhetors make use of the process of dissociation, where a unitary concept is divided into twodifferently-valued pairs, in defining embryonic stem cells. Scientific rhetors used dissociation toestablish embryonic stem cells as an ideal model for understanding the earliest stages ofdevelopment in mammals. Political rhetors used dissociation to undermine attempts byopponents of this research to define embryonic stem cells as the murder of a fetus or embryo.Third, both political and scientific rhetoric deploys an argument from hierarchy and its attendantambiguities to argue about different types of stem cells, especially embryonic and adult stemcells, and their capacity to attain the applications each group desires.