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(LifeSiteNews) — The introduction to this series set out the step-by-step process by which the human mind can arrive at the certain knowledge that everything proposed for our belief by the teaching authority of the Catholic Church is true.

The first step in this process is to come to know that God exists through the knowledge that our senses acquire from the world around us. This is the step spoken of by St. Paul, in his Epistle to the Romans:

For the invisible things of him, from the creation of the world, are clearly seen, being understood by the things that are made; his eternal power also, and divinity. (Rm 1:20)

Some philosophers have considered that the existence of God is so “clearly seen” that it is, in fact, self-evident. Others have held that God’s existence needs to be demonstrated by philosophical argument.

If the existence of God is self-evident, there is no purpose in attempting to demonstrate it by argument.

Therefore, we must begin by asking whether the existence of God is in fact self-evident.

What is God?

When we ask the question “does God exist?” we are presuming that the word “God” has a commonly accepted meaning. If it does not, no useful discussion of the question can take place.

Most people, whether they recognize His existence or not, understand the word “God” to signify a supreme being who created the universe and rules over it.

The Merriam-Webster dictionary, for example, provides the following definition of the word “God”:

The supreme or ultimate reality: such asthe Being perfect in power, wisdom, and goodness who is worshipped (as in Judaism, Christianity, Islam, and Hinduism) as creator and ruler of the universe.

Such an idea of God is all but universal in human history. Monotheistic religions express this idea most clearly, but polytheistic religions often retain belief in a supreme God who lies behind the other gods, and often one of the many gods has some characteristics of a supreme god. Pantheistic religions identify creation with a supreme being. And, when the atheist proclaims that they do not believe in God, they must have some idea of God in mind, otherwise the statement would be meaningless.

In general, whatever our differing beliefs, the word “God” does have an accepted meaning, and this is what makes philosophical discussion about His existence possible.

Might not all of this suggest that belief in God is somehow instinctive or self-evident?

Is the existence of God self-evident?

A truth is self-evident when it is recognized immediately and intuitively.

St. Anselm (c.1033-1109) thought that the existence of God was self-evident and put forward this view in his famous “ontological argument.”[1] Other versions of this argument were presented by later philosophers such as Descartes (1596-1640) and Leibniz (1646-1716).

St. Thomas Aquinas (c.1225-1274), on the other hand, held that the existence of God is not self-evident to us. That is, it is not immediately and intuitively known to us, without further rational demonstration.

St. Thomas explains that “No one can mentally admit the opposite of what is self-evident.”[2] That is, we cannot entertain in our mind an idea which is the opposite of a self-evident truth.

For example, our own existence is self-evident. We cannot even try to mentally admit the idea “I do not exist” without being aware that we are thinking and must therefore exist.

Similarly, it is self-evident that “the whole is greater than its parts.” Imagine a pizza cut into slices. You can imagine a whole pizza cut into quarters. You cannot however mentally admit the idea that the whole of a given pizza might in fact be smaller than one of the quarters of the same pizza. It is self-evident that this is not so.

St. Thomas asks whether we can admit the opposite of the idea “God exists” and concludes that we can. He writes:

The opposite of the proposition ‘God is’ can be mentally admitted: ‘The fool said in his heart, There is no God’ (Psalm 53:2). Therefore, that God exists is not self-evident.

St. Thomas is noting the reality that there are people in the world who do not believe in God. The very fact that it is possible for human beings to believe that God does not exist shows that it is not self-evident to mankind that God exists.

However, it is not quite as simple as that. St. Thomas goes on to explain that something can be self-evident in two ways: (i) “in itself but not to us,” and (ii) “in itself and to us.”

It is only according to the second mode that God’s existence is not self-evident.

How to know if a statement is self-evident ‘in itself’

St. Thomas writes:

A proposition is self-evident because the predicate is included in the essence of the subject, as “Man is an animal,” for animal is contained in the essence of man.

At first glance this sentence may seem complicated, but when the meaning of the unfamiliar terms is explained it becomes much clearer:

  • A proposition is a statement affirming or denying something, and consisting of a subject and a predicate. In this case: “Man is an animal.”
  • The subject of the above sentence is “Man.”
  • The predicate is that which is asserted of the subject, in this case, “is an animal.”
  • The essence of a thing is the fundamental definition of what it is. For example, the essence of man is “rational animal.” “Rational animal” distinguishes man from other animals (which are animal but not rational) and angels (which are rational but not animal).

Now let’s rewrite the first part of St. Thomas’s statement above, using these terms:

“Man is an animal” is self-evident because “is an animal” is included in “rational animal,” which is the essence of “man.”

That is to say, because man is by definition a “rational animal,” it is self-evident that he must be an animal.

On the other hand, it is not self-evident that, for example, a man has brown hair, a woman is very tall, or a boy has good eyesight. These things are not part of the essence “man.” A given “rational animal” could have red hair, be very short, or have bad eyesight.

How to know if a statement is self-evident ‘in itself and to us’

It is not the case that a statement which self-evident “in itself,” will in fact be self-evident “to us.”

This is because the essence of the subject or predicate may not be known to all.

In other words, if someone didn’t know the correct definitions of “man” and “animal,” it might not be self-evident to them that man was an animal. However, it would remain “self-evident in itself.”

This is what St. Thomas means when he writes:

If, however, there are some to whom the essence of the predicate and subject is unknown, the proposition will be self-evident in itself, but not to those who do not know the meaning of the predicate and subject of the proposition.

The existence of God is self-evident ‘in itself but not to us’

In the proposition “God is,” “God” is the subject and “is,” as in exists, is the predicate.

St. Thomas argues that the statement “God is” is self-evident “in itself” because “God is His own existence as will be hereafter shown.” St. Thomas is referring to the conclusion that God’s essence is His own existence; there is no distinction between “essence” and “existence” in God.

However, the above statement is not self-evident to us. It is a conclusion reached through a further exercise of a reasoning process (so don’t worry if you don’t understand it at present). It is only a person who has reached the understanding that the essence of God is identical to His existence, who understands that the predicate “is [existing]” is necessarily included in the subject “God.”

Therefore, the existence of God, while self-evident in itself, is not self-evident to us.

Man’s striving towards God   

St. Thomas does consider that men have a general and confused idea of God, even though his existence is not self-evident to us. This is because human nature has been directed by God towards its final end, which is happiness and therefore, ultimately, God. St. Thomas writes:

To know that God exists in a general and confused way is implanted in us by nature, inasmuch as God is man’s beatitude.

Man strives towards happiness, and thus towards Him who is our ultimate beatitude. Hence St. Augustine could write, in those famous words from his Confessions, “Thou hast made us for Thyself, O Lord, and our heart is restless until it rests in Thee.”

However, this general and confused knowledge of God – while it goes a long way to explaining the prevalence of belief in God discussed earlier – is not the same as clear certain knowledge of God’s existence. As St. Thomas explains:

This, however, is not to know absolutely that God exists; just as to know that someone is approaching is not the same as to know that Peter is approaching, even though it is Peter who is approaching; for many there are who imagine that man’s perfect good which is happiness, consists in riches, and others in pleasures, and others in something else.

If we are to know with certainty that God exists, we must seek to demonstrate this through rational argument, from things certainly known to our senses.

But is human reason adequate for the task of demonstrating that God exists?

This is the question that we will consider in the next installment of this series.


1 Detailed discussion of St. Anselm’s famous ontological argument would derail us here. In summary, however, it goes as follows: The idea of God that all men hold is “that than which nothing greater can be thought.” Now, what exists in reality is greater than that which is only a concept in the mind. Therefore, since “God is that than which nothing greater can be thought,” he must exist in reality. St. Anselm’s argument has criticized since he first proposed it and it has been all but universally rejected by Catholic philosophers. The main problem is that just because something can be conceived in the mind as greatest in the logical order does not prove that it exists in reality.
2 St. Thomas Aquinas, ST, I. q.2 a.1. All quotations from St. Thomas are from this article of the Summa Theologica.