"Both a fetus and a newborn certainly are human beings and potential persons, but neither is a ‘person’ in the sense of ‘subject of a moral right to life’. We take ‘person’ to mean an individual who is capable of attributing to her own existence some (at least) basic value such that being deprived of this existence represents a loss to her. This means that many non-human animals and mentally retarded human individuals are persons, but that all the individuals who are not in the condition of attributing any value to their own existence are not persons. Merely being human is not in itself a reason for ascribing someone a right to life. Indeed, many humans are not considered subjects of a right to life: spare embryos where research on embryo stem cells is permitted, fetuses where abortion is permitted, criminals where capital punishment is legal."
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