The Thomistic Argument for the Existence of God

If you are a believer who thinks it is worthwhile to know why you believe in God, I highly recommend Edward Feser’s book, Five Proofs of the Existence of God. If you are an atheist who thinks it is worthwhile to be sure that you are right, I highly recommend Dr. Feser’s book to you, as well.

If you keep up with apologetics, or the on-going dialogue between Christian apologists and atheists, you will probably be familiar with the following arguments for the existence of God:

1. The Kalam Cosmological Argument
2. The Moral Argument
3. The Fine-Tuning Argument

Most likely, you have heard these arguments put forward by William Lane Craig, undoubtedly the world’s leading apologist at present time. I would like to introduce you to another argument; one that I have never heard put forward by Dr. Craig, but undoubtedly known to him. This argument I first heard put forward by Dr. Feser and it is probably my favorite argument for the existence of God. This is the Thomistic Argument.

Essence and Existence 

Thomas Aquinas, that medieval scholastic philosopher, is well known for his distinguishing between essence and existence.

By essence, Aquinas was referring to what a thing is. I, Haden Clark, am a human, which is a rational animal. That is what I am. That is my essence.

By existence, Aquinas was referring to that a thing is. I, Haden Clark, exist. If you are reading this, you will just have to take my word for it!

At any rate, Aquinas argued that there is a real distinction between the existence of a thing and the essence of a thing. Some would attempt to refute this.

Consider a few things about essence and existence. We can grasp the essence of something even if it does not actually exist. You can grasp the essence of a unicorn, but unicorns do not exist. If there were no distinction between essence and existence, your grasping of the unicorn’s essence would entail that the unicorn actually exists. This is obviously false.

Another point on this subject is that if a thing’s essence and existence were one-and-the-same, that would mean the thing’s existence simply is its essence. This thing would be essentially existence. By definition, there could only be one of these things. Allow me to illustrate.

I am essentially human. However, I am not humanity itself. There is only one humanity because there can only be one humanity. Many humans, one humanity.

If everything was essentially existence that would mean everything was existence itself, which is impossible. There can only be one existence itself, while there are multiple existing things.

Indeed, it seems impossible that existence and essence could be the same thing. It seems they must be two different things of which we are composed. We each have an essence, and we each have existence; and these two things are not referring to the same thing.

Existence Must Come from Without

The next question should be obvious: How is it that we are composed of an essence and an existence?

Go back to my unicorn example. I can comprehend its essence, yet it does not actually exist. In order to exist, the essence must be granted existence.

Existence must be granted either from something else, necessarily, or by the essence itself.

The essence in question could not give itself existence, obviously, for it would have to already exist in order to give itself existence and that is absurd.

The other alternative is that an essence exists necessarily. That is to say, it could not fail to exist. Such a thing is certainly possible, but it is impossible that everything exists necessarily, for we observe that some things pass in and out of existence all the time. When a dog dies, its body decays and it ceases to be a dog. It ceases to be that which it was essentially, therefore existence could not be necessary to its essence. Sorry, if the example of a dog was too personal. I have two and love them dearly.

There are some things which clearly don’t exist necessarily. And nothing can grant existence to itself. Therefore, some things in the sensible world must be dependent on something external to their essence for their own existence.

At Every Point in Time

Notice what I have not said. I have not said that some things in the sensible world must have a cause of their beginning to exist, as if this cause is only needed to have happened at one point in the past. Not only that, but a thing whose essence is separate from its existence must be dependent upon something else for its existence at every point in time.

If thing X is dependent on thing Y for its existence, and thing Y does not exist necessarily (it could fail to exist), then it follows that thing Y must likewise be dependent on something else, thing Z, for its own existence at every point in time. And so on, and so on.

Must Begin

It is important to notice that this creates a hierarchal causal series. You and I are most likely more familiar with linear causal series. For example, I push a pool stick forward, it collides with the cue ball, the cue ball collides with the eight ball, and the eight ball collides with the corner pocket, just as I said it would.

After hitting the cue ball, the pool stick ceases to act upon the cue ball, yet the cue ball still collides with the eight ball, and so on. This is a property of a linear causal series. It is only dependent on the first cause at one point in time.

Consider a hierarchal causal series. My hand is moving a stick, which is moving a ball, which is moving a leaf. Therefore, if my hand releases the stick, everything “downstream” from my hand will also stop. That is because everything between my hand and the leaf were merely instruments. In-and-of-themselves, they have no causal properties. I was activating all of them at the same time.

Likewise, a thing whose essence is separate from its existence has no existence at any time in and of itself. It is always dependent on the cause of its existence, so that if the cause of existence were to cease, the thing would likewise cease to exist.

Another feature of this hierarchal causal series is that there must be a first cause in the order. With a linear series, it is possible that such a series will extend backwards forever, according to some philosophers. Even Aquinas granted this much.

However, it is impossible that a hierarchal causal series will extend backwards forever. The reason is what I already mentioned, namely that the agents in the series whose existences are not necessary are merely instrumental. They do not have the power to exist in-and-of-themselves, but something must, or else this series never gets off the ground to begin with. Nothing would ever begin to cause other things to exist, and there would be nothing, no existence.

What this means is that there is a being who exists necessarily and in fact whose essence just is existence. That is to say, this being simply is existence itself and imparts existence to all other things, and all other things are dependent upon this being for their existence at every point in time. This being exists necessarily and could not fail to exist, for if it did, everything that exists would also fail to exist.

Another feature of this being is that it is the only one. It is unique, or holy. It is impossible that there could be two things whose essence just is existence, as I mentioned above.

God Exists

To recap, we have concluded that there is a being whose essence is existence. This being gives existence to (creates) everything else at every moment in time. There is only one of this being. This being could not fail to exist, that is it exists necessarily, that is it is eternal.

Should I go on, or do these attributes sound familiar? In his book, Dr. Feser shows how a being whose essence is existence is also immutable, eternal, immaterial, incorporeal, perfect, omnipotent, fully good, and omniscient. That should definitely be familiar.

This is what we mean when we use the word God.