As a result of recent developments in reproductive and regenerative medicine, the moral status of the zygote and the embryo is becoming increasingly important. This paper considers them from the perspective of "potential persons" and investigates issues arising from this perspective. In particular I critically examine Tooley's personhood theory. First, I examine the "interest principle" as a core of Tooley's theory. (1) On the normative character of "interest", Tooley insists interest is necessary for an entity to have a right to life, but I insist interest is a necessary and sufficient condition for invoking others' moral consideration toward the interest-holder. (2) On the interest of potential persons, I prove the possibility of acknowledging it. (3) On the "particular interests principle", I argue conscious interest isn't the only possible interest for persons. Thus I show the "interest principle" isn't sufficient for determining personhood. I then propose another principle for determining personhood: an "ends in itself" argument based on "moral ability". Those who destroy an entity regard it as merely a means, and then being an end in itself is decisive for a person. Next, I discuss being "end in itself" based on moral ability and conclude we can regard potential persons as potential holders of that ability. Finally, I consider the concept of "potentiality". Tooley argues that the destruction of potential persons is morally equivalent to contraception. I clarify the assumptions underlying this argument by examining his "three potentialities" argument and "moral symmetry principle". He considers potentiality in terms of causality (the cause-effect relationship). When considering living entities, however, I propose we consider potentiality in terms of teleology (the parts-whole relationship, and the process aiming at goals). This paper aims to establish a framework for protecting potential persons as potential moral agents. It concludes that this is fully possible.
