“Why Aquinas Rejects an Infinite Series of Causes”
Illustrated!
In his famous “Five Ways of Proving the Existence of God”, Thomas Aquinas says that an infinite number of causes is impossible, and therefore there must be a first cause, which he calls “God”:
“But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover…
Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.”
But how does he justify this? Why does he think an infinite series is impossible? Isn’t he just begging the question by saying that there is a first cause? Isn’t he specially pleading by suggesting that everything has a cause, except one thing?
We humans are uncomfortable with the idea of infinity, but that doesn’t mean it is impossible. After all, we can easily imagine an infinite future, so why not an infinite past?
But Aquinas has a very good reason for saying that an infinite series is impossible.
First, we must be aware that Aquinas distinguishes between a cause of “becoming”, and a cause of “being.”
Gepetto might be the cause of the becoming of a shoe, that is, the coming-into-existence of the shoe, but he is not the cause of the continuing existence of the shoe. Gepetto could leave or die and the shoe will continue to exist.
A cause of the becoming of a lake would be the rain that causes a river, followed by the erosion that causes the lake to form, and so on in a chain of events, stretching back into the past. What we normally think of as a cause when we hear that word.
Event → Event → Event → Event → Event →
Aquinas actually agrees that such a series could stretch back infinitely into the past: “...it is not impossible to proceed to infinity ‘accidentally’ as regards efficient causes...as an artificer acts by means of many hammers accidentally, because one after the other may be broken.”
However, the cause of the continuing existence of a lake would be what keeps it in existence from moment-to-moment, in a chain stretching down in the present into more fundamental layers of reality. For example:
Lake
Warm Air
Heat from Sun
Nuclear reactions in Sun
Gravity of the Sun
Mass of the Sun
Higgs causing mass
Once we understand that Aquinas is talking about a chain of concurrent sustaining causes stretching “down” in the present, rather than a series of events stretching back into the past, it is easy to show why he thinks such a series cannot be infinitely long….
In other words, Aquinas is arguing for something that is “holding up the whole stack” in the present, regardless of how long the world has existed.
Consider a clamp holding an object. The clamp is spring loaded and will only stay closed if something else is holding it closed.
If it is being held shut by another spring-loaded clamp, then it won’t stay shut.
No matter how long the chain is, if they are all spring-loaded clamps, none of them will stay shut unless…
…there is a clamp that can be tightened that will hold them all shut. Call this a “permanent clamp”.
If there is no permanent clamp, then none of the spring-loaded clamps will be held shut.
And if there is an infinite chain of spring-loaded clamps, then there is no permanent clamp. And so none of the clamps will be held shut.
So if they are shut, then there cannot be an infinitely long string of clamps, because then there would be no permanent clamp, which there clearly is, somewhere down the line
We can now see what Aquinas meant:
“But this [chain of spring-loaded clamps] cannot go on to infinity, because then there would be no [permanent clamp], and, consequently, no [spring-loaded clamps will be held shut]; seeing that subsequent [spring-loaded clamps] [are held shut] only inasmuch as they are [held shut by the permanent clamp]…
Therefore it is necessary to arrive at a [permanent clamp], [held shut] by no other…