Defining embryo death would permit important research.

President Bush and many other opponents of using human embryos created by cloning or in vitro fertilization to produce stem cells for research hold an essentialist view: They think that a person's life begins as soon as the potential for a human being exists; thus, an embryo is simply a person who hasn't yet been born. Many proponents of using embryos for research take a more existential view: They believe that personhood emerges as the embryo develops. That difference is crucial because, as most ethicists would agree, if embryos were persons, research that necessarily resulted in their death -which would be the case with cloning -would be unethical regardless of the eventual benefit to science or medicine.