This essay briefly describes a few of the problems associated with using personhood language to defend the right to life of the pre‐implantation embryo. Arguing that an immaterial soul explains the personal identity of an embryo is problematic for many people because there is no apparent spiritual activity in the unborn. While some scholars argue that the embryo has the potential to act as an adult person and thus should be protected from harm, others contend that potentiality alone is insufficient (...) reason to ascribe special moral worth to the embryo in utero. For Thomas Aquinas, the soul is not only the life‐principle that organizes the human body, but it is also that by which the human being thinks and wills. By making suitable corrections to Aristotle's hylomorphic depiction of the soul–body relation, I suggest that a rational soul must be present from the moment of conception and that it is at the service of the person. What is of critical importance here is to accept that a human being is present from the moment of conception, something the vast majority of embryologists maintain, notwithstanding the inveiglement of those who state that the pre‐implantation blastocyst is simply a disorganized clump of cells. (shrink)