Abstract

In addressing bioethical issues at the beginning of human life, such as abortion, human embryonic stem cell research, and therapeutic cloning, a primary concern is to establish when a developing human embryo or fetus can be considered a “person”; for it is typically held that only persons are the subjects of moral rights, such as a “right to life.” The 13th century philosopher and theologian Thomas Aquinas defines a person as “an individual substance of a rational nature” (ST Ia.29.1); he further asserts that all human beings are persons (ST Ia.16.12 ad 1), but that an embryo or fetus is not a human being until its body is informed by a “rational soul.” Aquinas’s account of human embryogenesis has been generally rejected today due to its dependence upon medieval biological information. A number of scholars, however, have attempted to combine Aquinas’s basic metaphysical account of human nature with current embryological data to develop a contemporary Thomistic account of a human being’s beginning.