The Summa Theologica. Part II (2)

Aquinas’s theories on ensoulment in Summa Theologica do reveal more about the understanding of embryology during the period. His segment on souls indicates that while he believed souls were immediately united with the body, he believed that upon fertilization, human life begins with a vegetative soul. This vegetative entity was credited with having nutritive, augmentative, and generative powers, according to Aquinas, but would require further development before it would gain sensitive and intellectual capacities. The document does, however, argue for the immediate ensoulment upon the conception of Jesus Christ in Question 33, wherein Jesus was instantaneously given a rational, perfect soul, as opposed to the imperfect soul of the vegetative or animal stages, and a human form. Summa Theologica indicates that even scientific understanding of embryology was limited at this time, as there is very little accurate content in the document’s description of development in utero.

Currently, the Roman Catholic Church relies heavily on the Summa Theologica in its discussions on theology, philosophy, and morality, though it has since parted ways with Aquinas when it comes to the ideas of delayed hominization, vegetative souls, and the Aristotelian view of embryology, among others. Overall, the Summa Theologica provides great insight into the prevalent Christian views on human development and ensoulment during the Middle Ages, though it is less representative of today’s scientific and theological beliefs on these matters.