This question is related to Objections to Natural Theology at the Time of Vatican I

In contrast to the observance of natural phenomena in order to arrive at the conclusion that God exists, an ontological argument is one which draws the same conclusion from some source other than observation of the world; e.g., from reason alone.

The first such well-known argument, I believe, is the one attributed to St. Anselm, which (though multiple versions exist) I paraphrase as: "God is that Being Whom nothing greater can be conceived" — the proof of which can be assembled by reading his Proslogion. His argument which one may infer therein became famous; and then criticized a century or so later by St. Thomas Aquinas.

Many variations of Anselm's demonstration, as well as many criticisms, followed throughout the centuries.

In the twentieth century, the great logician Kurt Gödel (probably following the writings of Leibniz rather than that of Anselm), formalized a logical argument (with parallels to Anselm) which has been hailed as correct.

For those familiar with logical symbols, see, for example, Gödel Says God Exists and Proves It; and his proof is this:

Gödel's ontological proof

Of course, the validity of Gödel's argument (which is now widely accepted) depends on acceptance of his definitions (the Df.'s) and the inherent truth of his axioms (the Ax.'s).

QUESTION: What (if anything) has the Catholic Church declared (by say, either Council or papal encyclical) about affirming God's existence by reason alone; i.e., by some (apparently correct) ontological argument?

  • Is it really true that Godels argument is widely accepted? I don’t believe that’s the case in the academic world of the philosophy of religion
    – Luke Hill
    Commented Oct 27, 2023 at 17:35
  • Accepted in the sense of being logically correct.
    – DDS
    Commented Oct 27, 2023 at 21:31
  • when you say logically correct do you mean “valid” or “sound”?
    – Luke Hill
    Commented Oct 27, 2023 at 21:48
  • @LukeHill. "1)All dogs have 4 legs. 2)My pet is a dog. Therefore My pet has 4 legs" is logically correct. In reality it isn't correct (because my pet is a cat, or because it has only 3 legs, or because I don't have a pet, or … ). Commented Oct 28, 2023 at 2:44
  • @RayButterworth do you understand the difference between valid or sound? It seems like you are trying to articulate a valid argument but not a sound one.
    – Luke Hill
    Commented Oct 28, 2023 at 14:19

2 Answers 2


St. Thomas Aquinas

Although not mentioning St. Anselm by name, St. Thomas Aquinas formulates and refutes St. Anselm's "a priori argument"* in Summa Theologica I q. 2 a. 1 "Whether the existence of God is self-evident?" arg./ad 2:

Objection 2: Further, those things are said to be self-evident which are known as soon as the terms are known, which the Philosopher (1 Poster. iii) says is true of the first principles of demonstration. Thus, when the nature of a whole and of a part is known, it is at once recognized that every whole is greater than its part. But as soon as the signification of the word "God" is understood, it is at once seen that God exists. For by this word ["God"] is signified that thing than which nothing greater can be conceived. But that which exists actually and mentally is greater than that which exists only mentally. Therefore, since as soon as the word "God" is understood it exists mentally, it also follows that it exists actually. Therefore the proposition "God exists" is self-evident.


Reply to Objection 2: Perhaps not everyone who hears this word "God" understands it to signify something than which nothing greater can be thought, seeing that some have believed God to be a body. Yet, granted that everyone understands that by this word "God" is signified something than which nothing greater can be thought, nevertheless, it does not therefore follow that he understands that what the word signifies exists actually, but only that it exists mentally. Nor can it be argued that it actually exists, unless it be admitted that there actually exists something than which nothing greater can be thought; and this precisely is not admitted by those who hold that God does not exist.

*Prologion, quoted in Deely 2001 pp. 234-6
cf. Contra Gentiles lib. 1 cap. 10 & 11

First Vatican Council

It was not the mind of the First Vatican Council fathers to condemn "a priori" or "ontological" arguments of God's existence.

The First Vatican Council fathers considered formulating Dei Filius ch. 2 as follows:

God […] can be known certainly and demonstrated by the natural light of human reason, that is, by metaphysical, cosmological, and moral arguments.
—transl. in: Lawrence Dewan, O.P., “The Existence of God: Can It Be Demonstrated?,” Nova et Vetera 10, no. 3 (Summer 2012): 731–56, p. 734.

Explicitly mentioning "metaphysical, cosmological, and moral arguments" seemed unnecessary. Msgr. Gasser (bishop of Brixen, Tyrol, Italy) argued that knowledge by means of created things does not exclude "the celebrated ontological argument of St. Anselm":

What is suggested by this emendation can hardly be approved, the reason being a false supposition of this emendation. The reverend emendator in expressing it is of the opinion that our teaching is opposed to the best known arguments, or at least opposed to the metaphysical argument. But this supposition is altogether false: our teaching is in favour of these arguments and not against these arguments. For, if we say that God can be known by the natural light through creatures, that is, through the vestiges which are impressed on all creatures, much less do we exclude the image which is impressed on the immortal soul of man: hence, the metaphysical ["a priori" or "ontological"] argument is certainly not excluded. Who amongst us, when he shall have confirmed by his vote this doctrine which has been proposed by us, who indeed will think that he has condemned the celebrated ontological argument of St. Anselm, whatever he may think of that argument?
—transl. in: Dewan 2012 p. 734

The final version of Dei Filius ch. 2 has simply:

God […] may be certainly known by the natural light of human reason, by means of created things


Pope St. John Paul II references the First Vatican Council in the 1850s and a subsequent document from the Inquisition Errores Ontologistarum from 1861 in his encyclical Fides et Ratio.

Biblia Clerus shows the errors translated (via the web browser) from Latin:

  1. Immediate knowledge of habitual least, the human intellect is essential, so that without them there can be, since it is very light understanding.

  2. To be that, that in all things, and without which we understand nothing, it is to be divine.

  3. The universal from the part of the thing considered by God, they really do not differ from one another.

  4. The congenital of being simply as any other knowledge of the projecting information involves, such that it is all being under any respect is implicitly known.

  5. All other ideas are not only modifications of ideas that God as being simply understood.

  6. The matter were created in God as a part of the whole, not, indeed, in the whole of the formal, but in the whole of the infinite, the most simple, and the diminution of the division of the outside of the parts of which is, as it were, he puts himself without any of his own.

Creation can be explained, the very act of special, which he understands and wants as distinct from the determined creature, man v. g., Creation.

I think these are all anathematized. So it seems unlikely that the Church would be likely to definitively agree with Kurt Gödel (not that he would have agreed with the assertion). To my amazement, he was not an atheist although, like Darwin (and Darwin's pop) his ideas have been used extensively to look forth materialist ideologies more than anything else. Mainly the idea that we can't know anything definitively, which is the pop-sci definition of incompleteness.

I listened to a Catholic podcast a few weeks ago (possibly Godsplaining, Pints with Aquinas or the Catholic Man Show, they're all running together), Franciscan Priest where the hosts (who generally adhere to the Thomistic arguments against Anselm) were a little astonished by the other traditions who still buy the Ontological Argument.

Assuming these well-meaning friars and priests aren't heretics, I think there's still some wiggle room for pursuing many ideas about reason and creation. There are just some very clear red lines that can't be crossed when they devolve into materialism.

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