11 August 2016

On the Self-Evidence of God's Existence

What follows is an excerpt from a project I've been working on intermittently for the past three years. Strictly speaking, what's posted below is a commentary on Summa Theologiae Ia q. 2 a. 1. I imagine it will be useful to some people.

After identifying the subject matter, epistemic status, and methods of sacred doctrine as a science, St. Thomas is ready to begin the work of sacred doctrine itself: to come to know God through what he has revealed to mankind. As always, Thomas begins by dividing his task into parts, and so at the beginning of Question 2 we find a brief divisio textus for the entire Summa. (For a summary of the Summa, see the Introduction to this volume.)

The first tract of the Summa (qq. 2-26) analyzes the essence of God, i.e. “what it is to be God”. Thomas divides this tract (which is normally called De Deo Uno or “On the One God”) into three basic sections, which will be subdivided further as we proceed.

  • The first section discusses whether God exists. (q. 2)
  • The second section discusses what God is and is not. Here we attempt to understand what it is to be God, in relation to various qualities we know from creatures. Thus the question is: In what way does God have the same qualities we find in ordinary things, and in what way does he not have them? (qq. 3-13)
  • The third section looks at the various immanent operations of God—knowledge, will, life, mercy, providence, etc. (qq. 14-26)
  • The present question focuses on demonstrating the existence of God, and is divided into three articles, which could be summarized with the following points:
  • Is it necessary to prove the existence of God?
  • Is it possible to prove the existence of God?
  • Does God exist?

1.2.1 – Whether the existence of God is self-evident?

The first article asks whether the existence of God is per se notum.[1] As discussed above,[2] a claim is per se notum if it is known immediately, merely by considering the meaning of what is said. (The phrase literally means “known through itself”.) An example of this would be the claim “Triangles have three sides.” Everyone who knows what the sentence means mean recognizes immediately that it is true. The standard translation of the Summa renders “per se notum” as “self-evident”. While this is not a bad translation in itself, it is potentially misleading on account of the philosophical connotations of “self-evidence” in contemporary philosophy, with its strong Pyrrhonist tendencies (which have been active in most non-Catholic philosophy since the time of RenĂ© Descartes in the seventeenth century). We will discuss the difference below.

St. Thomas gives three objections that try to establish the claim “God exists” is per se notum. The first objection stems from the fact that knowledge of what is per se notum is naturally present in us. This does not mean that we are always actively knowing such things, but that whenever they are clearly proposed to us, we immediately grasp their truth by virtue of a natural habit or power of our understanding. But St. John Damascene says in his book On the Orthodox Faith that the knowledge of the existence of God is naturally inserted into everyone. Since this knowledge is in us by nature, it must be per se notum.

The second objection gives a summary of St. Anselm of Canterbury’s famous “ontological argument”.[3] The argument depends on the definition of the word “God” as “that than which nothing greater can be signified” (id quo maius significari non potest). However, a being that exists actually is greater than one that only exists in the mind. Therefore whatever the word “God” signifies must exist, since to claim that God does not exist would contradict the definition of the term. And since, as we said above, a proposition is per se notum if it is known just by understanding the meaning of the terms, the claim that God exists must be per se notum.

The third objection stems from Christ’s saying in the Gospel of St. John, “I am the way, the truth, and the life.”[4] Since Christ is God, and he refers to himself as “truth”, God is truth. Therefore to deny that God exists would be to deny that truth exists.[5] But if truth did not exist, then it would be true that “There is no truth.” Therefore there must be truth, and since we can know this claim merely by considering it, it is per se notum. But since the existence of truth is per se notum and God is truth, then the existence of God must be per se notum as well.

For the Sed Contra, St. Thomas invokes the authority of Psalm 52.[6] “The fool hath said in his heart” that God does not exist.[7] But if the existence of God were per se notum, no one could contemplate the question and conclude that God does not exist. So it would be impossible for the fool to say it in his heart. Since this is false, it follows that the existence of God is not per se notum.

In the Corpus, he points out that whenever a claim is per se notum, the predicate is included somehow in the notion of the subject. He then uses this fact to draw a distinction, which we will explain using the claim “Kangaroos are animals” as an example.

To anyone who knows what a kangaroo is, it is obvious that a kangaroo is an animal. Indeed, it belongs to the essence of a kangaroo to be an animal.[8] However, supposing someone didn’t know what a kangaroo was, but only knew that it was some sort of Australian thing that was living, the notion of a kangaroo available to them might not include “animal”. They might suppose that a kangaroo is a sort of Australian plant or fungus. Now, because to be an animal belongs to the essence of the kangaroo, if we look at the claim in itself, apart from any particular person considering it, “Kangaroos are animals” is per se notum—the predicate is contained in the essence of the subject. But when we look at the claim through the eyes of this or that particular person, with their own limited knowledge of kangaroos, in some cases it may be per se notum for them (if they know what a kangaroo is), but in some cases it may not.

This distinction reveals a very important difference between St. Thomas’s understanding of knowledge and the idea of self-evidence that was made popular by RenĂ© Descartes and has predominated in secular European philosophy since his time. For Descartes and those after him, a truly self-evident claim is absolutely certain, so that one cannot imagine oneself being mistaken about it. In Enlightenment philosophy, self-evident or “a priori” truths have an almost magical character. They serve as the fundamental building blocks of all knowledge, the source of all certainty about reality. For Thomas, however, claims that are per se nota have no magic powers. They are simply known through themselves, by considering the meaning of what is said, as the Latin meaning of the phrase suggests.

The self-evidence of a claim depends on the degree of understanding possessed by the person considering it. As a result, there are many claims which are per se nota in themselves, but which are not obvious to most people who consider them, simply because they do not sufficiently understand what is being discussed. If someone were insane, or tortured by demons, or in a perpetual dream state (as Descartes supposed himself to be), there is no guarantee that most things other than the most obvious would remain per se nota to him, or that one’s convictions about what is per se notum would be correct. However, in ordinary life one does not worry about the possibility that one is dreaming or insane or being tortured by demons, because one grasps very immediately by observing oneself that this is not the case. Basing one’s theory of knowledge on the presumption of one’s own insanity is, furthermore, not likely to be a good path to understanding how knowledge ordinarily works.

Once he has settled the distinction between claims that are per se nota in themselves and those which are also per se nota to us, Thomas applies the distinction to the question of God’s existence. In order for a claim to be per se notum to us, we must understand the essence of both the subject and the predicate, and see that the predicate is included in the essence of the subject. So, in order for the claim “God exists” to be per se notum to us, we would need to know the essence of God,[9] and be able to deduce his existence from that knowledge. But no one in the present life knows the essence of God.[10] Therefore even though God exists, this fact cannot be per se notum to us in the present life. On the other hand, we will see later on[11] that to exist belongs to the essence of God necessarily. Therefore, God’s existence is per se notum in itself, even though not to us. In the present life we must arrive at knowledge of God’s existence through things that are available to us in experience, and trace our way back to the one who created them.

Thomas responds to the first objection by explaining how the knowledge of God’s existence is implanted in human nature. Everyone knows that God exists, in an indistinct way, because everyone desires happiness, and it is in the nature of human happiness (whether or not most people realize it) that it can only be found in God. Because every person knows by nature that he wants to be happy, and everyone is able to recognize indistinctly that certain qualities belong to happiness, the more one is presented with these qualities, the clearer it will become that happiness is present. However, Thomas denies that this gives us knowledge of God’s existence simply speaking. It tells us that something is out there, and that we are tending toward it as our happiness, but the knowledge of what it is that we are tending toward is not immediately clear by nature, and many people suppose it to be something other than God.

The response to the second objection shows how St. Anselm’s argument fails. Thomas raises two objections to the argument. First, he points out that some people do not define God as “that than which nothing greater can be thought”, since they believe God to be a corporeal thing (a body), and obviously any existing body has definite dimensions and therefore we could conceive of one greater than it.[12]

Second, he shows that the argument assumes the conclusion it was trying to prove.[13] Granting that, if there is such a thing as “that than which nothing greater can be thought”, it would have to exist in order to meet the terms of its definition. But this does not settle whether the thing described by the definition exists in reality, only that if there is one, it must exist. But atheists deny that there is anything greater than which nothing can be thought, so the argument fails.

In response to the third objection, St. Thomas makes a very simple distinction. The truth which we can know to exist merely by considering it, is the ordinary, general truth which exists in judgments about the world. When Christ calls himself “truth”, however, he is referring to God’s nature as First Truth, which is distinct from truth in general, as will be discussed later on.[14]

Outline of the Article

God’s existence is per se notum, because:
• St. John Damascene says that knowledge of God’s existence is implanted in our nature.
• That thing greater than which nothing can be signified must exist, since, if it did not, we could signify something greater than it.
• The existence of truth is per se notum, and God is Truth, as Christ says.

A proposition is per se notum if the essence of its predicate is included in the essence of its subject:
• Any claim where the essence of the thing described really includes the essence of what is ascribed to it is per se notum in itself.
• But if the essence of the thing described is not adequately understood by the person considering it, then the proposition will not be per se notum to that person.
• God’s essence as such cannot be known to us in the present life.
• Therefore, even if God’s existence is per se notum in itself, it is not per se notum to us.

• We know by our nature that we desire our own happiness, which can only be found in God. Even though the closer we approach him, the more we grasp more clearly that our happiness lies in God, this truth is not per se notum to us.
• Even though the greatest conceivable being would have to exist in order to fit that description, the argument does not prove that such a thing does in fact exist.
• The existence of truth as it exists in ordinary judgments is per se notum; God is not this sort of truth, but First Truth.


[1]As stated earlier, per se notum is the singular form of the phrase, and per se nota is the plural.
[2]Cf. q. 1 a. 2.
[3]The classic statement of this argument is found in Chapter 2 of Anslem’s Proslogion, though it has been re-stated and defended under different formulations by many others in the course of history.
[4]John 14:6
[5]That God is, in some sense, “truth” will be discussed in q. 8 a. 5.
[6]The text of the Summa, like virtually all Catholic works written before the second half of the 20th century, uses the Psalm numbering found in the Latin Vulgate version of the Bible, which is based on numbering in the Septuagint, or Greek Old Testament. Most modern translations use the division of the Psalter found in the Masoretic Text. In this case, that means that the Psalm referenced would, in a normal modern Bible, be numbered 53, not 52.
[7]It is worth noting that St. Anselm discusses this exact verse in the very chapter where he gives his argument.
[8]In other words, being an animal is part of what makes a kangaroo a kangaroo.
[9]In other words, what God is in himself, or what it is about God that makes him God.
[10]Reasons for this will become clear as we proceed through the present tract.
[11]Cf. q. 3 a. 4.
[12]Cf. q. 7 a. 3.
[13]In philosophical jargon, this is referred to as the fallacy of begging the question.
[14]Cf. q. 16 a. 5
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