Medieval Philosophy

by Peter S. Adamson

Given that the Catholic Church is well known for insisting that a fully human life begins at conception, it’s intriguing to find that the Church’s most canonical thinker doesn’t think anything of the sort. Instead, Aquinas believes that the presence of a rational soul requires the presence of organs that can carry out its functions. Since this is lacking at early stages of fetal development, only the lower nutritive or plant-like functions are present at first. They are succeeded by the functions of the sensory and motive powers and finally by the advent of the distinctively human rational soul. The lower functions also have a different source than the powers of reason. They are brought out of the material provided by the parents, whereas the rational soul can be given only by God and so is created directly in the embryo at some point during gestation. With the arrival of each new kind of soul the previous form is destroyed or “discarded,” to be replaced with a new single and unified form, which, however, retains the powers available to the previous forms that were in the embryo