President George W. Bush and John F. Kerry have contradictory views regarding the killing of human embryos in order to obtain their stem cells for research purposes. Bush regards doing so as immoral and repugnant; Kerry thinks it imperative to do so and is ready to use taxes paid by citizens who agree with Bush to pay for such research. The Kerry campaign is now using a TV advertisement featuring Michael J. Fox, a well-known actor suffering from Parkinson's disease and another strong supporter of human embryonic stem cell research. Fox declares: “George Bush says we can wait. I say lives are at stake and it is time for leadership. That's why I support John Kerry for president.” Kerry has promised to spend $100 million a year on such research, claiming that “treatments could be right at our fingertips” if Bush had not banned the research. Among those agreeing with Kerry and Fox are Ruth R. Faden, Wagley professor of biomedical ethics at Johns Hopkins University and John D. Gerhart, C. Michael Armstrong Professor at John Hopkins Medical School. In an August 23 op-ed piece for the Washington Post and reprinted by the Oakland Tribune, the Alemeda Times and other papers these highly regarded academics listed the advantages promised by using human embryonic stem cells over using stem cells obtained from adults. At the conclusion of their essay Faden and Gerhart declared: “While we recognize and respect embryos as early forms of human life, we do not believe that embryos in a dish have the same moral status as children and adults,” and that, therefore, “the obligation to relieve human suffering binds us and justifies the instrumental use of early embryonic life.” Fader and Gerhart, however, fail to give any reasons to support their belief. Both authors recognize that human embryos are living members of the human species; they acknowledge that they are living and human rather than simian or bovine or canine or what have you. But they distinguish among members of the human species, deeming some, children and adults, the bearers of moral rights and others, early embryos, not. Why the difference? Like many in our society Faden and Gerhart evidently think that in order to count as a person one must have at least some degree of exercisable cognitive abilities and that human embryos, lacking such abilities, simply cannot count as persons. The reasoning behind this claim is fallacious. It fails to distinguish between a radical capacity or ability and a developed capacity or ability. A radical capacity can also be called an active, as distinct from a merely passive, potentiality. A human embryo, precisely as a member of the human species, has the radical capacity or active potentiality to discriminate between true and false propositions, to make choices, and to communicate rationally because these activities are species predictable. In order for a human embryo to exercise this capacity, however, the embryo must be allowed to live so that he/she can develop this capacity. But the capacity could never be developed were it not there to begin with. From this it follows that the human embryo is a human person with potential and not a potential person. Similarly, an eaglet lacks the developed capacity to soar high in the sky, but it has the radical capacity, rooted in its being as an eagle, to do those things that are predicable of the species eagle. Moreover, we can ask: “why should higher mental functions or the capacity or active potentiality for such functions be a trait conferring value on those who have it?” The proper answer is that such functions and the capacity for them have moral weight not because these functions are intrinsically valuable but because entities which have such potentiality are intrinsically valuable. And, if the entity itself is intrinsically valuable, then it must be intrinsically valuable from the moment that it exists. The claim that not all human beings are persons but that only those who possess exercisable cognitive abilities are to be so regarded is also marked by debates among its advocates over precisely which ability or abilities must be exercisable if an entity is to be classified as a “person.” The claim thus inevitably leads to arbitrary and unjust criteria for “personhood,” as the following considerations make clear. The rational abilities necessary for these cognitive functions are various, and come in varying degrees in human beings. If actual possession of such abilities is a necessary condition of the claim to be treated justly, questions will have to be faced precisely which abilities must be possessed, and how developed they must be before one enjoys the claim to be treated justly. But such questions can be answered only by arbitrarily choosing what abilities are to count as relevant and precisely how developed they must be to count. Arbitrary choices may be reasonable and unavoidable in determining some entitlements, but they are not such in determining the entities who are the very subjects of justice, and they certainly should not be the basis for life and death decsions. Arbitrariness here amounts to the claim that might makes right. The need for a non-arbitrary understanding of who are the subjects of justice requires us to assume that just treatment is owing to all human beings in virtue of their humanity. This indispensable assumption is eminently reasonable. Moreover, it seems reasonable that a key factor in allocating research dollars should be: which research is showing real progress in developing treatments and helping patients? Human embryonic stem cells have yet to treat one human patient, and their success in animal models has been very limited, whereas clinical trials using adult stem cells are already underway and showing progress in treating patients. And research on adult stem cells does not require the intentional killing of living members of the human species.