How much of St. Thomas Aquinas' teachings do I have to believe?


How much of St. Thomas Aquinas’ teachings do I have to believe to not be a heretic?



We are not required to believe any private revelation.

We are only required to believe what is the doctrine of the church.

Some saints have contributed to doctrine, and we are to believe that—but some saints have said some truly innane things and there is no impetus to believe that.


Aquinas’ teachings are not private revelation.


If they are not doctrine then they are not a requirement, period. Perhaps private revelation is not the right word but sainthood does not mean we are required to believe everything that came out of a person’s mouth.


Three other questions would need to be resolved before answering yours:

  1. How much of Aquinas’ teaching do you really understand?
  2. Which specific teachings are you speaking about?
  3. For what reason or motive are those teachings not acceptable to you?


You need to believe what the Church teaches as doctrine. If Aquinas taught the same on a point, follow Aquinas. If it doesn’t, you don’t need to follow Aquinas.

Aquinas did have a systematic way of explaining things which makes him a useful reference on Church Doctrine when the two overlap.


I guess a facetious answer would be: Those teachings that keep you from falling directly into heresy.


Neither are they magisterial, in and of themselves. :wink:

However, much of what he wrote is what is taught magisterially by the Church. So, if the Church teaches what Aquinas teaches, then we believe it… but only because the Church teaches it, not because Aquinas does.


All that are referenced and footnoted in the catechism; abbreviated as STh or SCG


Magisterial. That’s the word I was looking for.

There are things he taught which are not magisterial. We are not required to believe those things.

  1. I’m familiar mostly with some of Aquinas’ teaching on the nature of God, reality and causality.
  2. I generally think that his teaching makes sense, but some things like hylomorphism and saying that angels differ in species by necessity are troublesome.
  3. I think that splitting all reality into matter and form is an overly simplistic belief, and is difficult to reconcile with modern scientific knowledge. It makes sense that in Aquinas’ time it would be a good explanation of biological life and death, but given what we know today about chemistry, physics, biology, etc. and ignoring specific cases such as spirits, the Eucharist, and the mind-body problem, it seems not only problematic but lacking a good reason to believe it. Even for more mysterious physical phenomena such as animal and plant life, science seems to keep finding that these things can be explained solely by physics. Sure, we human beings use the idea of substances and accidents to make sense of the world, but to make the jump from substances existing conceptually to actually raises problems. Some examples include:

At what point does matter leaving a cell no longer belong to the organism? If a rock is broken in two, is it now one substance or two? Are God-made/nature-made substances of a distinct nature from man-made substances, and how? What about a complex object such as a building or computer? If you replace all the parts in a car, is it still the same car? And so on.

I understand the argument that while physical substances exist, we have limited understanding of them. But it seems to me that it is less problematic in most cases to believe that physical substances exist only conceptually, and that the physical world is a jumble of matter/energy and laws and forces.

It’s maddening to me that no one else on these forums seems to get my problems with hylomorphism.

In regard to the teaching on angels, I haven’t read much on it and it’s not especially important.

I agree that a lot of what Aquinas teaches makes sense, and I would be interested in studying his works. But I am bothered by the attitude I find among theologians that Aquinas is the “right” philosopher, and any dissent is wrong. I understand that some of what Aquinas taught is defined as doctrine. I also know that there is at least one case where there is non-heretical dissent on Aquinas (the nature of the resurrection of the body). It would be great if somewhere there is a list of what is and isn’t Church doctrine in Aquinas’ teaching. I don’t want to feel like I have to believe everything he taught.


Only the de fide teachings. :wink:


There is. We call it the Catechism of the Catholic Church.


Something is off here.

At first you claim that your problem is that Thomism is incompatible with modern science. But when you try to list your difficulties, they have nothing to do with “modern science”!

After all, in times of St. Thomas Aquinas the technology to split a rock (for example, hammers) did exist.

I’m starting to think that your real problem has little to do with St. Thomas Aquinas, and will not be solved with discussion of his philosophy…

OK, that might be a clue we need… So, you have an impression that animal life can be explained by Physics alone, and that science supports this, um, proposition? Can you tell us what makes you think so?

That sure would make sense if they would prove to be something other than problems with hylomorphism…


If you want to stay out of heresy, I don’t think you really have to study Aquinas. I would rather use the Catechism of the Catholic Church (CCC) as @itsjustdave1988 suggested. The CCC quotes St. Thomas Aquinas often. Sometimes after reading a passage in CCC, I will look up the references to get a better understanding. Most recently, for example, I read CCC on the morality of killing in self-defense, and then looked up Aquinas’ thoughts on it. I don’t always agree 100% with Aquinas. That doesn’t make me a heretic. It also doesn’t mean that I’m smarter than Aquinas. I just take as much as I can grasp, and I find that it helps me in my search for truth and faith.


You are not even required to read any of Thomas Aquinas’ works. With that said, I feel obliged (since Thomas Aquinas is my confirmation name) to tell you why he is such a trustworthy doctor of Catholic teaching…

  1. Innocent VI: “[Thomas Aquinas’] teaching above that of others, the canonical writings alone excepted, enjoys such a precision of language, an order of matters, a truth of conclusions, that those who hold to it are never found swerving from the path of truth, and he who dare assail it will always be suspected of error.”(Sermo de S. Thoma.)

  2. Leo XIII: “Among the Scholastic Doctors, the chief and master of all towers Thomas Aquinas…he is rightly and deservedly esteemed the special bulwark and glory of the Catholic faith… single-handed, he victoriously combated the errors of former times, and supplied invincible arms to put those to rout which might in after-times spring.” (Aeternis Paris)

  3. Urban V: “It is our will, which We hereby enjoin upon you, that ye follow the teaching of Blessed Thomas as the true and Catholic doctrine and that ye labor with all your force to profit by the same.” (Constitutio 5a, data die 3 Aug. 1368, ad Cancell. Univ. Tolos.)


Saint Thomas is a doctor of the church, which is an important distinction from other Saints:

Doctors of the Church:
This is a very special title accorded by the Church to certain saints. This title indicates that the writings and preachings of such a person are useful to Christians “in any age of the Church.” Such men and women are also particularly known for the depth of understanding and the orthodoxy of their theological teachings. While the writings of the Doctors are often considered inspired by the Holy Spirit; this does not mean they are infallible, but it does mean that they contributed significantly to the formulation of Christian teaching in at least one area.


For myself, Aquinas is difficult to read, simply because of his style and methodology. But that is my fault, not his. Frank Sheed and Edward Feser are easier philosophic reads.

As to hylomorphism, it applies only to human beings, since they are composed of body and soul, matter and spirit. But it is not a dualistic philosophy: body and soul are so intimately united as to form one substance, not two, and can only be pulled apart by violence, that is, death.

As for substance and accidents, from a physical / chemical perspective, all of science necessarily consists only in the study of accidents—that which is perceptible to the senses either directly or through instrumentation.


Hylopmorphism doesn’t only apply to human beings, and human beings are not the only creatures composed of body and soul or matter and spirit.


Well, I’ve pretty much forgotten everything I knew about hylomorphism. But angels are pure spirit, and animals are all matter, so what is left except human beings?

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