In our parish, we have a Q&A feature in our bulletin. The fodder for this is mined from a question container we keep in the student lounge. The question I drew for consideration last month was, “Didn’t St Thomas Aquinas teach that the human embryo didn’t receive a soul right away?”
Thomas based his stance on ensoulment on the rational beliefs of his day. The 13th century had no modern science as we understand it, and scholars of the time held that life arose spontaneously from non-living matter. When God infused a human soul into non-living matter, identifiably human qualities would appear. Without the benefit of microscopes and other techniques of observation within the human body, people of centuries ago were simply ignorant of the facts of conception. They had no knowledge of the genetic make-up of embryos. In the earliest stages of gestation, they did not perceive the human qualities that would be present if a human soul were there.
That said, Thomas held, as did most moral theologians, that abortion still constituted a grave sin. Despite not being perceived to have a soul, the contents of a woman’s womb and the semen of a man were still considered the “non-living” material that would produce a human being. This would be at the root of the Church’s teaching on masturbation: a moral Christian should honor what contributes to human life as she or he would honor human life itself.
Ensoulment has never been the Church’s main objection to abortion. It should also be pointed out that conception doesn’t always produce a unique human being. We know that twins or other multiples can emerge from a single fertilized human egg, or even that very early-stage multiples can fuse into one being. These facts do not detract from our moral beliefs on abortion.
Within my word-limit, did I cover the bases adequately? I’ve heard the quote (?) that Thomas held that male ensoulment took place at forty-day’s gestation and female at eighty. I’m leery about repeating that without attribution, so I didn’t mention it in my answer.
I continue to be perplexed by the focus on ensoulment in discussing what the Church has discussed on the nature of unborn life. On the other hand, it is fascinating conjecture to consider when we become ensouled beings. Neil and others may have more scholarly resources to offer in terms of what philosophers and theologians today are thinking. I step back from the limits of my own expertise on this one and concede the floor to others.