Does God Exist, Part Two

Does God Exist, Part Two February 27, 2022

In my previous article, I began a series on Thomas Aquinas’s five ways or arguments for the existence of God.

Aquinas’s first way is an argument from motion or change. Things move from potency to act; for example, a seed exists potentially as a tree, and a tree exists in act in relation to the seed. We saw that such a chain could not proceed on infinitely. Aquinas argues that an infinite regress of change would eliminate a first cause of change. Without a first cause of change, there would be no subsequent causes of change. This leads to the conclusion that there must be a first cause of motion or change, which itself is not changed. This cause is God.

In a similar fashion, Aquinas’s second way concerns efficient causes in the universe. As indicated in the first article on the five ways, an efficient cause is “The primary source of the change or rest” (Aristotle. Aristotle’s Physics. Oxford University Press, 1983) of an agent. For example, a parent is the efficient cause of a child.

I will begin by introducing the second way. I will then provide the argument itself. I will conclude by explaining and analyzing Aquinas’s argument.

The Second Way

The basic premise of this argument is predicated on the contingent nature of existence as well as the order of efficient causes in the universe. Aquinas also expands on his first way by arguing that not only does the universe require a cause, but that such a cause must also sustain the existence of the universe.

It is evident that what does not exist necessarily requires a cause outside of itself. That is, nothing can cause itself to come into existence. Since this claim is not self-evident to some atheists, it must be pointed out that for something to cause itself to exist would require that thing to exist before itself, which is, I think, self-evidently illogical. 

Aquinas then proceeds to argue that contingent things not only require an extrinsic cause, but also that those contingent things need a cause that sustains their existence. 

Similar to the first way, Aquinas shows the logical impossibility of an infinite regress of such a cause.

Here is how Thomas Aquinas formulates his second way:

“In the world of sense, we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself, for so it would be prior to itself, which is impossible. Now in efficient causes, it is impossible to go on to infinity because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause is several, or only one. 

Now to take away the cause is to take away the effect. Therefore, if there is no first cause among efficient causes, there will be no ultimate or intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.” (Aquinas, Thomas. Summa Theologica Complete in a Single Volume. 2018).

Analyzing the Second Way

In the article on Aquinas’s first way, we saw that he categorized efficient causes into essential and accidental. The essential efficient cause is at the heart of this particular argument. 

Aquinas points out that everything in the universe depends on another for its existence. As in the first way, it is important to note that Aquinas does not argue that everything requires a cause, but only those things which do not exist necessarily. That is to say, if something does not exist eternally, it must be created. Once this is understood, we can eliminate the silly question of who created God, since God is that which exists eternally and necessarily. 

Yet, Aquinas’s second way claims not only that contingent beings require a cause but that they also require a cause or causes to sustain their existence. Human beings are not only contingent, but they are also dependent on external factors to survive. All life relies on the earth, and the earth is dependent on the solar system, and so on. 

Aquinas then points out that a dependent chain of efficient causes cannot regress infinitely. The reason is that an infinite regress means no initial efficient cause. There can be no subsequent effects if there is no initial (or essential) efficient cause. Without an uncaused first cause, nothing exists. Therefore, Aquinas concludes that there must be a being who exists necessarily as the cause of existence, which is God.

Moreover, the effect exists only so long as the essential efficient cause sustains it. A fire can only burn in the presence of specific properties (e.g., oxygen and flammable material). Remove those particular elements, and the fire ceases to exist. Applying that principle to the universe, if the efficient cause that sustains the universe does not exist, then the universe would cease to exist. 

Thus, Aquinas asserts that God, as the uncaused first cause, not only is the creator of the universe but sustains its existence at every moment. Accepting this aspect of the argument effectively denies deism which asserts that God creates the universe but does not sustain or intervene in His creation.

At this point, it may appear that the second way differs only from the first way in how it is presented. However, the difference lies in whereas the first way showed the necessity of a being that causes change but itself is not changed, the second way concerns itself with why anything exists at all. As the second way makes evident, not only does the universe require a cause, but it also requires a cause that sustains its existence. 


In the preceding article, I have provided an introduction to Thomas Aquinas’s second way for the existence of God. 

We have seen how the second way broadens the necessity of a first cause of existence to include the need that such a cause sustain its creation.

In part three of this series, I will discuss Aquinas’s third way.

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