The Thomistic Cosmological Argument

The Thomistic cosmological argument attempts to reason from the existence of dependent beings to the existence of God. According to this argument, the present existence of dependent beings can only be explained by an independent being that currently and actively sustains them in being. We can formulate one version of the argument as follows:

  1. There are dependent beings.
  2. If something is a dependent being, then its continued existence must be sustained by something else.
  3. If a dependent being is sustained by something else, then either the chain of sustained beings regresses infinitely or terminates in an independent being that is not itself sustained.
  4. The chain of sustained beings cannot regress infinitely.
  5. Therefore, the chain of sustained beings must terminate in an independent being that is not itself sustained.

Let’s consider the premises.
Premises 1 & 2
A being is dependent if its continued existence is conditional upon facts external to itself. Upon reflection, we see that the world is filled with instances of such beings. For example, an ice sculpture is a dependent being in the sense that its continued existence is conditional upon the temperature level. If the temperature rises above freezing, then the sculpture will melt and cease to exist. Likewise, you and I are dependent beings in the sense that our continued existence is conditional upon a myriad of physical conditions, including temperature, pressure, entropy, and the strong nuclear forces holding our atoms together. If these conditions are removed or radically altered, then we will cease to exist.
As these examples show, if something is dependent, then its existence must be continually sustained by something else. Something that is dependent does not stop being dependent. As long as it remains in being, it continues to require a cause to sustain its existence. Its originating cause of existence may cease to exist, but its continued cause of existence must always exist alongside of it. Thus, an ice sculpture may continue to exist if its sculptor dies, but it cannot continue to exist if the right temperature does not hold. Likewise, my parents are my originating cause, and I can exist even if they die, but my continued existence is dependent on factors such as temperature, pressure, entropy, and the various forces holding together the atoms and molecules that compose me. If these are removed, then I cease to exist.
Here is another way to see this point: if something is dependent, then it isn’t in its nature to exist. In other words, it doesn’t have to exist. Its “default state” is non-existence. But if it does exist, then there must be something external to it that accounts for its existence. What’s more, its existence must be continually accounted for by this external source of being. Why? Well, since existence isn’t part of its nature, it doesn’t have within itself the source of its being. An example may help. Consider a puppet. It isn’t in the nature of the puppet to move. But if the puppet is in fact moving, then it must be because it is being continually acted upon by an external cause. If that external cause stops acting on the puppet, then the puppet ceases to move.
Existence is much the same. Since it’s not in our nature to exist, the fact that we do exist must be explained by an external cause that continually sustains us in being. When thinking about existence, we must remember that existence is not a single event. It is a continual process that occurs over time. So long as anything dependent exists, its existence must be sustained by external causes that work to keep it in being.
Premises 3 & 4
When it comes to sustaining causes, either the whole process of sustaining causation either stops somewhere or goes on forever without end. Now one might be tempted to entertain the latter alternative, but upon close reflection the idea that there could be an infinite regression of sustained beings is rationally untenable.
Here’s why: in any chain of sustained beings, each member is a dependent being. Now as we saw earlier, dependent beings are such that they don’t have their own power to exist: they must be continually given this power by an external cause. Accordingly, each member of the chain must possess derivative causal power: they must first be given existence before they can impart it to others. But if every member of the chain is like that, then no member of the chain can impart existence. This is because each member of the chain requires something that no other member of the chain possesses. It will do no good to say that each member of the chain gets its existence from the preceding member of the chain, since the question at hand is how the power to impart existence exists within the entire chain when no member has that power inherently.
This problem is not avoided by positing an infinitely long chain: adding more dependent beings don’t change the fact that they don’t have inherent causal power of their own. Consider an infinite series of gears. No matter how many gears there are in the series, they will never move themselves. This is because it is not within the nature of gears to move: they must be given this power by something outside of the chain of gears. If they are moving, then, it must be because there is a cause acting upon it from outside of the series of gears.  Similarly, a paintbrush with an infinitely long handle will not move by itself, nor will an infinite series of boxcars move themselves without an engine.
There has to be an independent being outside of the chain of dependent beings to impart the initial causal power to get the whole chain started. This being must of necessity be independent, for otherwise we run into the problem just considered. It must have causal power in its very nature, such that it is not dependent on anything else. Moreover, given that dependent beings must be continually sustained in existence, this independent being must be continually imparting causal power to the chain of dependent beings.
Premise 5
Putting all of this together, the chain of sustained beings must terminate in an independent being that is not itself sustained. We are left with an ultimate sustainer of all dependent beings. In the words of the Apostle Paul, it is a being in which “we live and move and have our being.”
But why must this cause be God? The reason is simple: the independent being described by the argument is one whose nature is to exist. Since its nature is to exist, it cannot possibly be lacking in anything, since to lack something is to lack existence of some kind. It must, in other words, possess maximal existence. But to possess maximal existence is to possess all positive properties (e.g. power, knowledge, and goodness) to their fullest extent while lacking nothing. Hence, the independent being described by the argument must also be perfect, as it is complete with respect to its being.
Since God is by definition a perfect being (that’s just what we mean by God), it follows from the argument that God exists.
Further Reading

  • Michael Augros, Who Designed the Designer? (Ignatius, 2015)
  • David Beck, “The Thomistic Cosmological Argument” in Beckwith, Craig, and Moreland, To Everyone an Answer (InterVarsity, 2004)
  • Edward Feser, The Last Superstition: A Refutation of the New Atheism (St. Augustine’s, 2008)
  • Edward Feser, Aquinas: A Beginner’s Guide (Oneworld, 2009)
  • Edward Feser, “The New Atheists and the Cosmological Argument” Midwest Studies in Philosophy (2013)
  • Norman Geisler, Philosophy of Religion 2nd ed (Baker, 1988)
  • Norman Geisler, Christian Apologetics 2nd ed (Baker, 2013)
  • Winfried Corduan, “The Cosmological Argument” in Geisler and Meister, Reasons for Faith (Crossway, 2007)