Thomas Aquinas’s name gets dropped in quite a few pro-abortion arguments.  Roe v. Wade referenced Aquinas.  President Biden referenced Aquinas.  There’s even a popular undercurrent of pseudo-history you can find around the internet that appeals to Aquinas to portray the Middle Ages as this golden age of abortions where your local herbalist was always at the ready to sell the neighborhood abortion drugs at the drop of a hat.  But why is Aquinas referenced with such regularity?  

Aquinas didn’t believe that a fetus was genuinely human until one to three months after the pregnancy began.

And that’s true!  He didn’t.  We’ll get to why in just a minute.  But the strange thing about all of the Aquinas citations is that the people who reference Aquinas (on both sides of the aisle) don’t seem to know much about him.  They know he’s a famous Christian and philosopher and if they can convince people he’s on their side, boy, that would be a knockout punch in their favor.  But that’s the thing; they’re not curious about what he actually has to say for himself.  They want to explain their own position and drop his name in there when it’s convenient.  When they bother to give any citations, they tend to be from secondary sources (which is so lazy when when the person in question wrote as much as Aquinas did) and even when there are direct citations, his most famous works are usually referenced, rather than the most relevant to the actual topic at hand.  So, I wanted to give Aquinas a fair opportunity to speak on the matter.  What did Aquinas actually believe about abortion? 

It’s a big question, so I’m going to tackle it in three different pieces: Aquinas on the Beginning of Human Life, Aquinas on Sex, and Canon Law in the Day of Aquinas.

And if you’re looking for spoilers, here’s the big picture: working within the bounds of popular science in his day, Thomas did believe that human life starts to be genuinely human between one and three months into a pregnancy (depending on the child’s gender). This qualified early-term abortion as a crime other than murder. That said he still lists it as a crime against nature regardless of when it happens, and he worked within a system where it was legally punishable by law at any stage during the pregnancy. Aquinas’s question wasn’t “Is abortion a crime,” so much as it was, “How serious a crime is abortion at each stage?”

Let’s dig in.

Aquinas on the Origins of Life

If we want to talk about Aquinas and abortion, the first place to go is his commentary on Peter Lombard’s Sentences.  It’s not as well known as his famous Summa Theologica, but it’s the only place where he goes from speaking in abstract terms about human development to a description that’ so concrete that it lists specific timeframes for that development.  The context here is a debate about Jesus’s development during Mary’s pregnancy. When was that little fetus Jesus? Was he the Son of God right from the moment of conception?  Or did he become the Son of God at a certain moment in the pregnancy?  Classic Aristotialian thought held that sperm grew into a person in the incubating space of the womb (indicated in the word’s derivation from the Greek σπέρμα sperma meaning “seed”). That process took 40 days for a male child and 90 days for females.  If you hold to that Aristotlian science (and Aquinas certainly did), you end up with a question: did Jesus have a proto-human phase in which he successively became a human from a sperm?  Or was he just instantaneously there in the womb as a person through the power of the Holy Spirit?  He answers as follows:

[A]ccording to the faith, Christ’s conception must be held to have happened instantaneously, for human nature was not assumed before it was perfected in its species, since its parts were not assumable except by reason of the whole, as is evident from what was said in Distinction 2. … For this reason we must consider that conception to have been instantaneous, so that these things existed in the same instant: the conversion of that material blood into flesh and the other parts of Christ’s body; the formation of the organic members and the soul being infused in the organ-bearing body; and the assumption of the ensouled body into the unity of the divine person.

Now, in others these things occur successively, such that a male child’s conception is not completed until the fortieth day, or a female’s until the ninetieth, as the Philosopher says in History of Animals, [book] 9. But in the completion of the male body Augustine seems to add six days, which are distinguished as follows, according to him in his Letter to Jerome. For the first six days the seed has a likeness resembling milk; in the next nine days it changes to blood; then in twelve days it solidifies; in eighteen days it is formed to the complete lines of the members; and from then on the rest of the time until the time of delivery it grows in size. Thus the verse: Six days as milk, three times three as blood, two times six forms the flesh, three times six the members. However, in Christ’s conception, the matter that the Virgin supplied immediately took the form and figure of the human body, as well as the soul, and was assumed into the unity of the divine person (Commentary on the Sentences, Book 3, Distinction 3, Question 5, Article 2).

You can see him reference some of his previous work (Book 3, Distinction 2, Article 3) in the quote there to try to establish that Jesus Christ was not just the soul, but the body.  In the incarnation, there was a perfect union of God and man, not a material body that developed separately and then a soul that came along after the fact. There had to be a legitimate, full union between the two natures. He admits that for normal humans, the Aristotelian norm of 40 and 90 days before you’re fully human is true, but Christ’s exceptional incarnation led to him just popping into being through the power of the Holy Spirit, rather than developing from a sperm.

All of this science is very strange to us and obviously wrong. He doesn’t even know that eggs exist; only sperm. Even so, you can see how this really clearly gives us the framework to determine when a fetus is a human child. In his words, it’s “ensouled” after the first few weeks. Before that, an organic creature is developing, but it’s not one that’s human just yet.

If we just look at this solitary piece, abortion feels like a pretty rational move for a Christian that’s following in his footsteps, right?  Ah, but we can’t just pluck out his pieces about human development (a proportionally small piece of his works) and ignore the lion’s share of what’s left and declare ourselves to be thinking in his tradition.  Let’s keep going to see why Aquinas actually did not support abortion.

Aquinas on Sex

Now that we know what Aquinas thinks about the development of a fetus, we need to understand what he thinks about the procreative act itself.  On this topic, Aquinas really is absolutely a man of the medieval Chrisitan world.  And what did medieval Christians think about sex?  Well, to them, it was absolutely intertwined with having babies.  You couldn’t rightly separate the sensual aspect from the procreative aspect without stumbling into sin.  Now, obviously I’m not saying that everyone in the middle ages acted according to that worldview and never cheated on their spouse or whatever other thing you can imagine.  Of course they did.  People don’t always live up to the ideals of their society, even if they claim to ascribe to them.  But when it comes to the ideals, doctrines, and philosophy of the time, there can’t be any doubt that any effort to enjoy sex without an openness to procreation was sinful.

And why?  Well, the medieval world, and especially Thomas Aquinas, thought in terms of natural law.They believed the world had a natural sort of logic to it that was built in by God.  As you went about living your life, you were expected to look at each object and each act to consider why it exists.  Why did God make this?  What was his purpose?  Are you acting in a way that’s consistent with the logic of God’s creation?  Or are you twisting things around to serve your own wants, rather than God’s intended purpose?

That’s really abstract, so let’s work through an example.  An obvious one is food.  What is the logic of food?  Food exists to give us nourishment.  The process of eating it might be pleasurable (and there’s nothing inherently wrong with that), but if we’re going to live by the logic of the thing, the process of eating should never be separated from its natural end: we eat to be nourished.  If we start to enjoy it without that end in sight, that’s when we start to sin.  Are you enjoying Doritos because you’re hungry?  That’s great!  Are you enjoying Doritos when you’re already full but you just want to keep munching because they’re delicious?  That’s sin.  You’re losing sight of why God gave us food and just enjoying it out of gluttony.

Now, take that logic and apply it to sex.  Why does sex exist?  To have kids.  That’s the natural, logical end of the process.  If you wanted to have sex righteously, you were expected to look towards the end (babies), rather than just indulging for the pleasure of the process itself.  That was lustful and a misuse of what God gave us.  Not only was this logic very popular throughout the medieval world, but it was very popular with Thomas Aquinas.  As a matter of fact, the argument and examples that I just gave (sans Doritos) are straight out of his magnum opus, Summa Theologica, when he’s rejecting the idea that all “venereal acts” are inherently sinful:

A sin, in human acts, is that which is against the order of reason. Now the order of reason consists in its ordering everything to its end in a fitting manner… Now just as the preservation of the bodily nature of one individual is a true good, so, too, is the preservation of the nature of the human species a very great good. And just as the use of food is directed to the preservation of life in the individual, so is the use of venereal acts directed to the preservation of the whole human race (Question 153, Article 2).

Also, notice that he felt the need to debate whether or not there can be non-sinful sex.  That should tell you something else about the medieval world verses our own!  While we debate, is there any sex that is morally wrong, they were debating whether there was any sex that is morally right!  A very different starting place

This alone helps us shift gears when we’re thinking about Aquinas and abortion.  Aquinas would not have wanted anyone to have sex if they weren’t open to having children.  That would be against the nature of the act and sinful sex, even for a married couple.  Aquinas says as much directly in his Commentary on the Sentences when he addresses one of Peter Lombard’s quotes about birth control:

As for those who procure poisons to induce sterility, they are not marriage partners, but fornicators. (Sent. IV, 31.3 (184). 1.

Although this sin is grave, and to be counted among wicked deeds, and against nature (for even beasts desire offspring), nevertheless it is less grave than murder, since a child conceived could be prevented in another way.  Nor is such a person to be judged irregular, unless he should now procure an abortion for the child about to be born  (Book 4, Distinction 31, Question 2, Article 3).

And in that quote, you can see how he starts to move from birth control to abortion in applying the same logic. We are given food to be nourished.  We are given sex to procreate.  Why is a person made pregnant?  Is it to end the pregnancy?  No.  That would qualify as going against the natural logic of pregnancy in the most direct way possible.  Natural law philosophy was one of Aquinas’s biggest emphases, so if we want to introduce him to conversations about abortion, we have to remember that background first and foremost before we can deal with any of the specifics.

Church Law in the Days of Aquinas

But now that we’ve set the stage on some of Aquinas’s basic convictions as an Aristotilian thinker and a natural law enthusiast, we need to acknowledge the actual law of the medieval church during the era that he was at work.  As famous as he was, he influenced the teachings, and the teachings most definitely influenced him, so what did the church actually hold during the eras in question?  And I do want to acknowledge that this is a really complicated thing to research.  A shocking amount is not readily accessible if you don’t speak Latin.  Luckily, Paul Harrington wrote an excellent summary of laws pertaining to abortion over time in church history in The Linacre Quarterly that makes the depths of medieval church law accessible to anyone. While we have a particular interest in church law during the lifetime of Aquinas (1225-1274), a broader picture of what was going on in the medieval and Roman Catholic church won’t hurt our understanding either.

Looking at church law over time, for a little over a thousand years, the church considered abortion to be legally identical to murder and the standard punishment was usually excommunication.  It’s hard for us to wrap our minds around something like excommunication, since there’s not really an equivalent today. If we get kicked out of our congregation, good riddance! We’ll just go to the church down the street! But if we want to really understand their mindset, it’s crucial to recognize just how serious a punishment like that was in that timeframe.  An excommunicated person was cut off from the church until they had fully repented, meaning they couldn’t go to worship with their family and community.  They couldn’t participate in the sacraments.  They couldn’t get married.  They couldn’t offer prayers for dead relatives.  They couldn’t get buried. And if they died while excommunicated, Hell was the destination.  Excommunication was the most severe punishment you could get from the church.  This was serious.

A little after the turn of the millennium, we do see that distinction between an animated and inanimate fetus make it’s way into law. It first appeared in 1116.  A bishop named Ivo of Chartres first introduced it, and that distinction was taken up by a legal scholar named Gratian and printed in the legal textbook that became the standard for decades moving forward, Decretum.  It continued in Roman Catholic law for 753 years until Pope Pius IX ended that distinction in 1869.  During this period, if you got an abortion outside of the 40 day limit for males or 90 day limit for females, you were a murderer.  If you got an abortion within the limit, you had committed quasi-murder or homicide (the language varied depending on specifics at the time).  As the name implies, the punishments were less severe for quasi-murder.  For example, in 1159, your punishment was 3 years of penance if you aborted an inanimate fetus, verses the 7 years of penance or more that you would receive for aborting an animated fetus (which was the punishment for murder). And that’s just one specific instance. Sometimes, the punishment was a lifetime of excommunication. Sometimes it was left up to regional leaders. You get the idea. The important thing to note is that there was a legal distinction that made one a greater sin and the other a lesser sin. Some of the other abortion-centric laws in this timeframe didn’t acknowledge the distinction. For example, a piece of legislation by Regino of Prum in 1211 introduced a law that anyone caught selling drugs to induce abortion (at any stage of development) was guilty of murder. On the whole though, the distinction stands (for those who are curious, the distinction never really seems to have made a meaningful appearance in the Protestant world).

Notice that Aquinas’s position was the dominant position of the church during this time.  Abortion was always sinful.  The distinction in church law was never used to imply otherwise.  The distinction came up because people wanted to know how severe the sin of abortion was. Was it murder? Was it quasi-murder? Was it grave sin? Is it a lifetime excommunication or a period of penance? What punishment fits the crime?

Conclusion

Whew!  That’s a lot to take in.  Honestly, every time I learned more about this topic, it genuinely pushed me to deeper levels of understanding.  It was wild to see how recent our modern understanding of biology is, how church law was enacted in different eras, and how philosophy and theology have influenced one another in so many different ways.  I didn’t come to this question knowing the answer.  I came because I wanted to see firsthand what the truth was, and after some sifting around, I found more of it than I started with.  And I got to rediscover that history is so weird!  People in different times had such different ideas that are hard to wrap our minds around.

Nevertheless, at the end of it all, I have to wonder whether pro-abortion appeals to Aquinas are a product of ignorance or if they’re knowingly made in bad faith.  The solitary point of agreement is that he did not think human life began instantaneously after sex.  After that point, it’s all downhill.  In spite of that agreement, he did agree to a relatively early date where the child was fully human.  He considered abortion a crime against nature at best and murder at worst (depending on the timing).  He upheld and helped to shape a system of philosophy and canon of law that literally included it as a punishable offense.  Is this really the best person to appeal to?

As humans, we have the unique privilege of looking at this world around us and trying to figure it all out.  That’s wild!  We get to learn and read and try our best to come to knowledge of the truth.  A basic part of wielding that privilege well is acknowledging when we disagree with others and why we do.  When we misrepresent the legacy of others to make our ideas more palatable to those who would otherwise disagree, we’re participating in a lie, and the truth is never uncovered by lying.

Other great recommendations for those who want more:
Summa Theologica Ch. 118
Summa Contra Gentiles, Book 2, Ch. 65 and up
Abortion: Part VIII, Paul V. Harrington
A Great Free Translation of All Things Aquinas by the Aquinas Institute